S. D. thanks R&#233;gion Midi-Pyr&#233;n&#233;es and Universit&#233; F&#233;d&#233;rale de Toulouse for doctoral fellowship. D. Z. thanks Chinese Scholarship Council for doctoral fellowship. A. M. thanks COLFUTURO for doctoral fellowship. S. B. thanks the ANR programme JCJC &#34;ICC&#34; and Prof. A. Leon for fruitful discussion.

CAUTION: Please consult material safety data sheets (MSDS) of the chemicals before use. Please use appropriate safety practices when performing the following reactions and personal protective equipment. A special attention must be dedicated to the use of the vacuum line and gas pressure system.
1. Synthesis of compound 2 from CO2 in a nuclear magnetic resonance (NMR) tube
<ol>
	<li>Stock solution of Fe(H)2(dmpe)2: dissolve 4.6 mg of Fe(H)2(dmpe)221,22 in 1 mL of tetrahydrofuran (THF)-d8. 
	NOTE: dmpe = 1,2-bis(dimethylphosphino)ethane</li>
	<li>In a glove box, charge an NMR tube with 15.9 mg of 9-borabicyclo[3.3.1]nonane (9-BBN) and 100 &#181;L of a stock solution of Fe(H)2(dmpe)2 (1 mol%).</li>
	<li>Add 0.5 mL of tetrahydrofuran (THF)-d8.</li>
	<li>Close the tube and bring it outside the glove box.</li>
	<li>Connect the tube to a gas system and place it at 25 &#176;C for 15 min to equilibrate the temperature of the solution inside the tube. 
	NOTE: The gas system connects the CO2 bottle to both the vacuum line and the NMR tube. The connections are with Teflon tube and Swadgelock connectors (see Figure 1 for a scheme of the setup). This system enables to add the pressure defined at the regulator at the desired temperature.</li>
	<li>Add 1 atm of CO2.</li>
	<li>Leave for 3 min under a dynamic pressure of CO2 and close the tube.</li>
	<li>Leave the tube at 25 &#176;C for 45 min. 
	NOTE: At this step bis(boryl)acetal 1 is generated inside the NMR tube in 85% yield (see representative results for the NMR analysis).</li>
	<li>Stock solution of amine: dissolve 177.3 mg of 2,6-(diisopropyl)phenylamine in 1 mL of THF-d8.Once compound 1 is generated, open the NMR tube inside a glove box and add 55 &#181;L of a stock solution of the 2,6-(diisopropyl)phenylamine, corresponding to 1 equivalent of the generated bis(boryl)acetal 1.</li>
	<li>Close the tube and hand shake it for 10 s.</li>
	<li>After 20 min, confirm the formation of imine 2 by 1H NMR analysis (Figure 2). Use hexamethylbenzene (roughly 10 mol% vs 9-BBN) as an internal standard to determine the NMR yield.</li>
</ol>
2. Synthesis of compound 3 from CO2 in a Fisher Porter
<ol>
	<li>Charge a Fisher Porter with 320 mg of 9-BBN, 9.4 mg of Fe(H)2(dmpe)2 and a magnetic stirring bar21,22.</li>
	<li>Add 10 mL of THF.</li>
	<li>Close the Fisher Porter and bring it outside the glove box.</li>
	<li>Place it at 25 &#176;C for 15 min to equilibrate the temperature of the solution.</li>
	<li>Connect the Fisher Porter to the gas system and add 1 atm of CO2. 
	NOTE: The gas system connects the CO2 bottle to both the vacuum line and the Fisher Porter. The connections are with Teflon tube and Swadgelock connectors (see Figure 1 for a scheme of the setup). This system enables to add the pressure defined at the regulator at the desired temperature.</li>
	<li>Leave for 3 min under a dynamic pressure of CO2, close the tube and stir it at 25 &#176;C for 45 min. 
	NOTE: This stage corresponds to the selective generation of bis(boryl)acetal 1 from CO2 hydroboration in 85% yield.</li>
	<li>After 45 min, open the Fisher Porter in a glove box and add a solution of 380 mg of triazol-5-ylidene in 6 mL of THF.</li>
	<li>Outside the glove box, charge the Fisher Porter with 3 atm of CO2.</li>
	<li>Stir the solution at 60 &#176;C for 60 min under a dynamic pressure of 3 atm of CO2.</li>
	<li>Let the solution cool down to room temperature.</li>
	<li>Remove the volatiles under vacuum and wash the residue with 3x 2 mL of diethylether (Et2O) at 0 &#176;C to obtain CO2 adduct 3 as a white powder (Figure 3).</li>
	<li>To generate monocrystals, place a concentrated THF/pentane solution at -37 &#176;C for 24-48 h.</li>
</ol>
3. Synthesis of compound 4 from CO2 in a Fisher Porter
<ol>
	<li>In a glove box, charge a Fisher Porter tube with 159 mg of 9-BBN, 4.7 mg (1 mol%) of Fe(H)2(dmpe)2 and a magnetic stirring bar.</li>
	<li>Add 5 mL of THF.</li>
	<li>Close the Fisher Porter and bring it outside the glove box.</li>
	<li>Place it at 25 &#176;C for 15 min to equilibrate the temperature of the solution.</li>
	<li>Connect the Fisher Porter to the gas system and add 1 atm of CO2.</li>
	<li>Leave 3 min under a dynamic pressure of CO2, close the Fisher Porter and stir it at 25 &#176;C for 45 min. 
	NOTE: This stage corresponds to the selective generation of bis(boryl)acetal 1 from CO2 hydroboration in 85% yield.</li>
	<li>After the generation of 1, open the Fisher Porter in a glove box and add 54 mg of triazol-5-ylidene.</li>
	<li>Outside the glove box, stir the solution at 80 &#176;C for 40 min to generate a mixture of compounds containing compound 4.</li>
	<li>Remove the solvent and dissolve part of the residue in 0.6 mL of THF-d8.</li>
	<li>Filtrate the solution with a syringe equipped with a PTFE filter (0.2 &#181;m) and place it in an NMR tube for analysis. Use hexamethylbenzene (roughly 10 mol% vs 9-BBN) as an internal standard to determine the NMR yields.</li>
</ol>
4. Alternative synthesis of compound 4 from d,l-Glyceraldehyde
<ol>
	<li>In a glove box, charge a Schlenk tube with 50 mg of d,l-Glyceraldehyde, 135 mg of 9-BBN and a magnetic stirring bar.</li>
	<li>Add 4 mL of THF. 
	CAUTION: Upon dissolution of the compound, H2 evolution occurs.</li>
	<li>Close the Schlenk with a septum and stick a needle into it to allow the constant release of H2 formed.</li>
	<li>Stir the white suspension at room temperature for 24 h inside the glove box.</li>
	<li>Add 165 mg of triazol-5-ylidene.</li>
	<li>Stir 3 h at room temperature. All residues solubilize during that time.</li>
	<li>Remove the volatiles under vacuum.</li>
	<li>Solubilize the residue in a minimum amount of Et2O (1 mL) and place the solution at -37 &#176;C for 12 h.</li>
	<li>Compound 4 precipitates. Remove the filtrate by filtration and dry the precipitate under vacuum.</li>
	<li>Isolate compound 4 as a white powder in 72% yield.</li>
</ol>

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A., Rovis, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Catalytic+Asymmetric+Cross-Aza-Benzoin+Reactions+of+Aliphatic+Aldehydes+with+N-Boc-Protected+Imines.">Catalytic Asymmetric Cross-Aza-Benzoin Reactions of Aliphatic Aldehydes with N-Boc-Protected Imines.</a> Angewandte Chemie International Edition. 51 (24), 5904-5906 (2012).</li><li>Maji, B., Mayr, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structures+and+Reactivities+of+O-Methylated+Breslow+Intermediates.">Structures and Reactivities of O-Methylated Breslow Intermediates.</a> Angewandte Chemie International Edition. 51 (41), 10408-10412 (2012).</li><li>Bugaut, X., Glorius, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organocatalytic+umpolung:+N-heterocyclic+carbenes+and+beyond.">Organocatalytic umpolung: N-heterocyclic carbenes and beyond.</a> Chemical Society Reviews. 41 (9), 3511-3522 (2012).</li><li>Paul, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Breslow+Intermediates+from+Aromatic+N-Heterocyclic+Carbenes+Benzimidazolin-2-ylidenes,+Thiazolin-2-ylidenes).">Breslow Intermediates from Aromatic N-Heterocyclic Carbenes Benzimidazolin-2-ylidenes, Thiazolin-2-ylidenes).</a> Angewandte Chemie International Edition. 57, 8310-8315 (2018).</li><li>Holland, M. 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The authors have nothing to disclose.

Herein, we present the one-pot two-step versatile transformations of CO2 into complex products. The first step of the method concerns the selective 4 e- reduction of CO2 with a hydroborane reductant. This step is critical because selectivity toward the 4 e- reduction is challenging. Very few systems have been reported that describe the selective generation of bis(boryl)acetal23,24,25. In our case, an iron hydride complex catalyzes this selective 4 e- reduction of CO2 with 9-BBN, affording compound 1, under mild conditions (25 &#176;C) and with very short reaction time (45 min) (Figure 2)18. Our study shows that the reaction conditions are very important. In our hand, each attempt to change the concentration, solvent, CO2 pressure and temperature led to the decrease of the yield in compound 1. A longer reaction time is also detrimental because it leads to over-reduction to the methanol level or evolution of the bis(boryl)acetal into several oligomeric compounds. From our experience, it is necessary to verify the outcome of this reduction step by in situ 1H NMR characterization. The reproducibility of the method needs to be probed over several runs.
The in situ condensation reaction of the intermediate 1 with a bulky aniline gives rise to the corresponding imine 2 (Figure 2). This is a straightforward method and compound 2 is readily formed in a high yield (83%). This reaction can also be used to probe the efficiency of the reduction step. This method is the only method enabling the synthesis of imine function from CO2. Moreover, intermediate 1 was proved to be a versatile source of methylene in various condensation reactions leading to the formation of C-N, C-O, C-C and C=C bonds18. This method thus offers a straightforward way of using CO2 as a surrogate of formaldehyde in condensation reactions26.
Intermediate 1 reacts with Ender&#39;s carbene to afford compounds 3 or 4, depending on the reaction conditions (Figure 3)20. With the support of in-depth experimental and theoretical study, we were able to explain the observed reactivity. In this case, compound 1 does not react as formaldehyde since boryl moieties remain in compounds 3 and 4. This feature arises from the formation of an unprecedented O-Borylated Breslow intermediate (Figure 3)27,28,29,30,31,32. This intermediate is not observed experimentally but may act as a bifunctional Lewis acid/Lewis base activator toward CO2 to afford compound 3 or leads to the homocoupling of two more carbon centers to afford compound 4. In both products, chiral centers are generated and in the case of compound 4, the two chiral centers, C2 and C3, are obtained in a diastereoselective manner, thanks to the presence of the bridging boryl fragment.
The advances presented herein were possible thanks to the one-pot two-step method employed and to the high and versatile reactivity of intermediate 1 generated from the selective 4e- reduction of CO2. Following a similar method to further improve the scope and the complexity of the synthesized molecules, on-going works are dedicated i) to tune the properties of bis(boryl)acetal in using other hydroborane reductants and ii) to probe different coupling conditions in using other organo-catalysts.

In light of the large interest in using CO2 as a sustainable carbon source1,2,3, the purpose of the method is to transform CO2 into a variety of value-added products.
Intense researches aim at functionalizing CO24,5 or reducing it into formic acid (2 e- reduction), carbon monoxide (2 e- reduction), methanol (6 e- reduction) or methane (8 e- reduction)1,6. The interception of the 2 e- reduction product with amine, notably, gives rise to formamide and methylamine7,8,9. These areas of research are the most advanced so far. However, the scope of accessible functions and the added value of products formed compared to the starting materials remains rather minimal.
To circumvent this limitation, we focused i) on the 4 e- reduction of CO2 and ii) on applying a one-pot two-step procedure. The interest of the one-pot two-step procedure is to limit compatibility issues between the two steps and consequently to broaden the type of reactivity which could be conducted after the first step of reduction. We targeted the 4 e- reduction of CO2 because formaldehyde -the simplest 4 e- reduction product- is a particularly reactive and versatile carbon source10,11. It is used in condensation reaction as a methylene source and can be polymerized into carbohydrates. The latter -called formose reaction- is an impressive transformation generating carbon chain and chiral carbon centers solely from formaldehyde and is of high interest for synthetic-12,13 and prebiotic-chemistry14,15,16.While we are able to observe free formaldehyde from CO2 hydroboration17, its selective generation under homogeneous conditions is still unprecedented. Instead of formaldehyde, we developed the synthesis of bis(boryl)acetal compound 1 from the selective double hydroboration of CO218,19.
In one-pot two step processes we prove herein that, in the same pot, this intermediate 1 i) reacts as a surrogate of formaldehyde in condensation reactions18 or ii) gives rise to a modified formose-type reaction20. In this latter reaction, C-C coupling and chiral carbon centers are obtained.

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	<tbody>
		<tr>
			<td>Wilmad quick pressure valve NMR tube 5 mm diam.</td>
			<td>Sigma-Aldrich</td>
			<td>Z562882-1EA</td>
			<td></td>
		</tr>
		<tr>
			<td>Filtre-seringue PTFE hydrophobe &#216; 25 mm pores 0,22 &#181;m</td>
			<td>UGAP</td>
			<td>2528593</td>
			<td></td>
		</tr>
		<tr>
			<td>Fisher Porter</td>
			<td>Home made system</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>9-borabicyclo[3.3.1]nonane dimer</td>
			<td>Sigma-Aldrich</td>
			<td>178713</td>
			<td></td>
		</tr>
		<tr>
			<td>FeCl2 (anhydrous)</td>
			<td>Strem</td>
			<td>MFCD00011004</td>
			<td></td>
		</tr>
		<tr>
			<td>d,l-Glyceraldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>G5001</td>
			<td></td>
		</tr>
		<tr>
			<td>2,6-(diisopropyl)phenylamine</td>
			<td>Sigma-Aldrich</td>
			<td>374733</td>
			<td></td>
		</tr>
		<tr>
			<td>dimethylphosphinoethane</td>
			<td>Strem</td>
			<td>MFCD00008511</td>
			<td></td>
		</tr>
		<tr>
			<td>Tetrahydrofuran</td>
			<td>Carlo Erba</td>
			<td></td>
			<td>solvent</td>
		</tr>
		<tr>
			<td>Diethyl ether</td>
			<td>Carlo Erba</td>
			<td></td>
			<td>solvent</td>
		</tr>
		<tr>
			<td>Pentane</td>
			<td>Carlo Erba</td>
			<td></td>
			<td>solvent</td>
		</tr>
		<tr>
			<td>Tetrahydrofuran D8</td>
			<td>Eurisotop</td>
			<td>D149FE</td>
			<td></td>
		</tr>
	</tbody>
</table>

versatile co2 transformations into complex products: a one-pot two-step strategy

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products and notably to generate chiral carbon centers. The crucial first step consists in the selective double hydroboration of CO2 catalyzed by an iron hydride complex. The product obtained with this 4 e- reduction is a rare bis(boryl)acetal, compound 1, which is subjected in situ to three different reactions in a second step. The first reaction concerns a condensation reaction with (diisopropyl)phenylamine affording the corresponding imine 2. In the second and third reaction, intermediate 1 reacts with triazol-5-ylidene (Enders&#39; carbene) to afford compounds 3 or 4, depending on the reaction conditions. In both compounds, C-C bonds are formed, and chiral centers are generated from CO2 as the only source of carbon. Compound 4 exhibits two chiral centers obtained in a diastereoselective manner in a formose-type mechanism. We proved that the remaining boryl fragment plays a key role in this unprecedented stereocontrol. The interest of the method stands on the reactive and versatile nature of 1, giving rise to various complex molecules from a single intermediate. The complexity of a two-step method is compensated by the overall short reaction time (2 h for the larger reaction time), and mild reaction conditions (25 &#176;C to 80 &#176;C and 1 to 3 atm of CO2).

Successful generation of bis(boryl)acetal compound 1 is assessed by 1H NMR analysis with the characteristic methylene pick at 5.54 ppm in THF-d8 (Figure 4a). Successful generation of compound 2 is assessed by 1H NMR analysis with the characteristic AB signal (&#948; = 7.73 (d, 1H, 2JH-H = 18.4 Hz, CH2), 7.30 (d, 1H, 2JH-H = 18.4 Hz, CH2) for the two inequivalent protons of the methylene in THF-d8 (Figure 4b). Successful generation of compound 3 is assessed by 1H NMR analysis in THF-d8 (Figure 4c). The most notable signals are the CHCO2 at 5.34 ppm, and the CH of the BBN fragment at 0.26 and -0.65 ppm. Successful generation of compound 4 is assessed by 1H NMR analysis in THF-d8. As shown in Figure 4d, compound 4, in situ generated from CO2, is notably characterized by a doublet at 4.64 ppm (3JH-H = 7.9 Hz, H3) and a pseudo-t at 3.36 (2JH-H = 9.7 Hz, 3JH-H = 9.5 Hz, 1H, H1b). In the isolated compound 4 from d,l-Glyceraldehyde, the four proton signals of the C3 chain are clearly observed (Figure 4e) and the three carbon atoms of the chain are characterized in the 13C{1H} NMR analysis at 76.9 (C2), 74.0(C3) and 71.5(C1) ppm (Figure 5).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60348/60348fig1.jpg" /> 
Figure 1: Gas system. Scheme of the gas system enabling the addition of a defined pressure of CO2 at a given temperature. <a href="https://www.jove.com/files/ftp_upload/60348/60348fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/60348/60348fig2a.jpg" /> 
Figure 2: Reductive functionalization of CO2. Synthesis of compounds 1 and 2. <a href="https://www.jove.com/files/ftp_upload/60348/60348fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/60348/60348fig3a.jpg" /> 
Figure 3: Carbene-mediated C-C bond formation. Synthesis of compounds 3 and 4. <a href="https://www.jove.com/files/ftp_upload/60348/60348fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/60348/60348fig4a.jpg" /> 
Figure 4: 1H NMR analyses of compound 1-4, recorded at room temperature in THF-d8. (A) In situ generated compound 1, (B) in situ generated compound 2, (C) isolated compound 3, (D) in situ generated compound 4 from CO2, (E) isolated compound 4 from d,l-Glyceraldehyde. <a href="https://www.jove.com/files/ftp_upload/60348/60348fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/60348/60348fig5a.jpg" /> 
Figure 5: Representative characterization of compound 4 isolated from d,l-Glyceraldehyde. 13C{1H} NMR analysis recorded at room temperature in THF-d8; inlet: zoom of the C1-C3 area. <a href="https://www.jove.com/files/ftp_upload/60348/60348fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy at JoVE.com

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations are conducted in a one-pot two-step procedure for the synthesis of complex molecules. The selective 4 e- reduction of CO2 with a hydroborane reductant affords a reactive and versatile bis(boryl)acetal intermediate which is subsequently involved in condensation reaction or carbene-mediated C-C coupling generation.

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products ...

versatile-co2-transformations-into-complex-products-one-pot-two-step

Research

JoVE Journal

Chemistry

7.9K Views.  Université de Toulouse, CNRS. CO2 transformations are conducted in a one-pot two-step procedure for the synthesis of complex molecules. The selective 4 e- reduction of CO2 with a hydroborane reductant affords a reactive and versatile bis(boryl)acetal intermediate which is subsequently involved in condensation reaction or carbene-mediated C-C coupling generation.

Video: Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. Specifically, the sapphire cell enables visual data collection from multiple loadings to solve a set of material balances to precisely determine phase composition. Ternary phase diagrams can then be established to determine the proportion of each component in each phase at a given condition. In principle, any ternary system can be studied although ternary systems (gas-liquid-liquid) are the specific examples discussed herein. For instance, the ternary THF-Water-CO2 system was studied at 25 and 40&#160;&#176;C and is described herein. Of key importance, this technique does not require sampling. Circumventing the possible disturbance of the system equilibrium upon sampling, inherent measurement errors, and technical difficulties of physically sampling under pressure is a significant benefit of this technique. Perhaps as important, the sapphire cell also enables the direct visual observation of the phase behavior. In fact, as the CO2 pressure is increased, the homogeneous THF-Water solution phase splits at about 2 MPa. With this technique, it was possible to easily and clearly observe the cloud point and determine the composition of the newly formed phases as a function of pressure.
The data acquired with the sapphire cell technique can be used for many applications. In our case, we measured swelling and composition for tunable solvents, like gas-expanded liquids, gas-expanded ionic liquids and Organic Aqueous Tunable Systems (OATS)1-4. For the latest system, OATS, the high-pressure sapphire cell enabled the study of (1) phase behavior as a function of pressure and temperature, (2) composition of each phase (gas-liquid-liquid) as a function of pressure and temperature and (3) catalyst partitioning in the two liquid phases as a function of pressure and composition. Finally, the sapphire cell is an especially effective tool to gather accurate and reproducible measurements in a timely fashion.

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus is a unique tool to study, without sampling, phase behavior under a wide range of pressures. Using a cathetometer, very precise volume measurements can be recorded to measure liquid expansion and phase composition. Thus, this synthetic method enables the study of (1) phase equilibria of multi-component mixtures and (2) the partition behavior of catalyst or model compounds as a function of pressure.

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. ...

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10- nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

Various procedures are outlined to prepare atomically defined templates for epitaxial growth of complex oxide thin films. Chemical treatments of single crystalline SrTiO3 (001) and DyScO3 (110) substrates were performed to obtain atomically smooth, single terminated surfaces. Ca2 Nb3 O10- nanosheets were used to create atomically defined templates on arbitrary substrates.

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain ...

A Direct, Early Stage Guanidinylation Protocol for the Synthesis of Complex Aminoguanidine-containing Natural Products

The guanidine functional group, displayed most prominently in the amino acid arginine, one of the fundamental building blocks of life, is an important structural element found in many complex natural products and pharmaceuticals. Owing to the continual discovery of new guanidine-containing natural products and designed small molecules, rapid and efficient guanidinylation methods are of keen interest to synthetic and medicinal organic chemists. Because the nucleophilicity and basicity of guanidines can affect subsequent chemical transformations, traditional, indirect guanidinylation is typically pursued. Indirect methods commonly employ multiple protection steps involving a latent amine precursor, such as an azide, phthalimide, or carbamate. By circumventing these circuitous methods and employing a direct guanidinylation reaction early in the synthetic sequence, it was possible to forge the linear terminal guanidine containing backbone of clavatadine A to realize a short and streamlined synthesis of this potent factor XIa inhibitor. In practice, guanidine hydrochloride is elaborated with a carefully constructed protecting array that is optimized to survive the synthetic steps to come. In the preparation of clavatadine A, direct guanidinylation of a commercially available diamine eliminated two unnecessary steps from its synthesis. Coupled with the wide variety of known guanidine protecting groups, direct guanidinylation evinces a succinct and efficient practicality inherent to methods that find a home in a synthetic chemist&#39;s toolbox.

Here, we present a protocol for direct, early stage guanidinylation that enables rapid total synthesis of aminoguanidine-containing small organic molecules. An advanced synthetic intermediate used in the synthesis of a blood coagulation factor XIa inhibitor was prepared using this protocol.

The guanidine functional group, displayed most prominently in the amino acid arginine, one of the fundamental building blocks of life, is an important ...

A Quantitative Glycomics and Proteomics Combined Purification Strategy

There is a growing desire in the biological and clinical sciences to integrate and correlate multiple classes of biomolecules to unravel biology, define pathways, improve treatment, understand disease, and aid biomarker discovery. N-linked glycosylation is one of the most important and robust post-translational modifications on proteins and regulates critical cell functions such as signaling, adhesion, and enzymatic function. Analytical techniques to purify and analyze N-glycans have remained relatively static over the last decade. While accurate and effective, they commonly require significant expertise and resources. Though some high-throughput purification schemes have been developed, they have yet to find widespread adoption and often rely on the enrichment of glycopeptides. One promising method, developed by Thomas-Oates et al., filter aided N-glycan separation (FANGS), was qualitatively demonstrated on tissues. Herein, we adapted FANGS to plasma and coupled it to the individuality normalization when labeling with glycan hydrazide tags strategy in order to achieve accurate relative quantification by liquid chromatography mass spectrometry and enhanced electrospray ionization. Furthermore, we designed new functionality to the protocol by achieving tandem, shotgun proteomics and glycosylation site analysis on hen plasma. We showed that N-glycans purified on filter and derivatized by hydrophobic hydrazide tags were comparable in terms of abundance and class to those by solid phase extraction (SPE); the latter is considered a gold standard in the field. Importantly, the variability in the two protocols was not statistically different. Proteomic data that was collected in-line with glycomic data had the same depth compared to a standard trypsin digest. Peptide deamidation is minimized in the protocol, limiting non-specific deamidation detected at glycosylation motifs. This allowed for direct glycosylation site analysis, though the protocol can accommodate 18O site labeling as well. Overall, we demonstrated a new in-line high-throughput, unbiased, filter based protocol for quantitative glycomics and proteomics analysis.

A high-throughput protocol was developed for combined proteomics and glycomics purification and LC-MS/MS quantification in plasma. Deamidation analysis of N-linked glycosylation motifs was specific to deglycosylated sites. Accurate quantitation of N-glycans was achieved by coupling filter aided N-glycan separation to the individuality normalization when labeling with glycan hydrazide tags strategy.

There is a growing desire in the biological and clinical sciences to integrate and correlate multiple classes of biomolecules to unravel biology, define ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

Synthesis of a Water-soluble Metal&amp;#8211;Organic Complex Array

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate glycosyl donor. Following azido-nitration of a glycal, the product 2-azido-1-nitrate ester can be hydrolyzed under microwave-assisted irradiation. This transformation is usually achieved using strongly nucleophilic reagents and extended reaction times. Microwave irradiation induces hydrolysis, in the absence of reagents, with short reaction times. Following denitration, the intermediate anomeric alcohol is converted, in the same pot, to the corresponding 2-azido-1-trichloroacetimidate.

A 2-azido-1-nitrate-ester can be converted to the corresponding 2-azido-1-trichloroacetimidate in a one-pot procedure. The goal of the manuscript is to demonstrate utility of the microwave reactor in carbohydrate synthesis.

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate ...

Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional batch reactors, coined stop-flow micro-tubing (SFMT) reactors. In SFMT, chemical reactions that require high pressure can be screened in parallel through a safer and convenient way. Cross-contamination, which is a common problem in reaction screening for continuous flow reactors, is avoided in SFMT. Moreover, the commercially available light-permeable micro-tubing can be incorporated into SFMT, serving as an excellent choice for light-mediated reactions due to a more effective uniform light exposure, compared to batch reactors. Overall, the SFMT reactor system is similar to continuous flow reactors and more superior than batch reactors for reactions that incorporate gas reagents and/or require light-illumination, which enables a simple but highly efficient reaction screening system. Furthermore, any successfully developed reaction in the SFMT reactor system can be conveniently translated to continuous-flow synthesis for large scale production.

A protocol for organic reaction screening using stop-flow micro-tubing (SFMT) reactors employing gaseous reactants and/or visible-light mediated reactions is presented.

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional ...

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species

&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. Recently, we have developed a two-step strategy for ketone enolate umpolung that has enabled the development of methods for chlorination, azidation, and amination using azoles. In addition, we have developed C-C bond&#8211;forming arylation and allylation reactions. At the heart of these methods is the preparation of the intermediate and highly reactive enolonium species prior to addition of a reactive nucleophile. This strategy is thus reminiscent of the preparation and use of metal enolates in classical synthetic chemistry. This strategy allows the use of nucleophiles that would otherwise be incompatible with the strongly oxidizing hypervalent iodine reagents. In this paper we present a detailed protocol for chlorination, azidation, N-heteroarylation, arylation, and allylation. The products include motifs prevalent in medicinally active products. This article will greatly assist others in using these methods.

A two step one-pot protocol for the umpolung of ketone enolates to enolonium species and addition of a nucleophile to the &#945;-position is described. Nucleophiles include chloride, azide, azoles, allyl-silanes, and aromatic compounds.

&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. ...

Achieving Moderate Pressures in Sealed Vessels Using Dry Ice As a Solid CO2 Source

Herein is presented a general strategy to perform reactions under mild to moderate CO2 pressures with dry ice. This technique obviates the need for specialized equipment to achieve modest pressures, and can even be used to achieve higher pressures in more specialized equipment and sturdier reaction vessels. At the end of the reaction, the vials can be easily depressurized by opening at room temperature. In the present example CO2 serves as both a putative directing group as well as a way to passivate amine substrates, thereby preventing oxidation during the organometallic reaction. In addition to being easily added, the directing group is also removed under vacuum, obviating the need for extensive purification to remove the directing group. This strategy allows the facile &#947;-C(sp3)-H arylation of aliphatic amines and has the potential to be applied to a variety of other amine-based reactions.

Achieving Moderate Pressures in Sealed Vessels Using Dry Ice As a Solid CO2 Source

Here we present a protocol for performing reactions in simple reaction vessels under low-to-moderate pressures of CO2. The reactions can be performed in a variety of vessels simply by administering the carbon dioxide in the form of dry ice, without the need for costly or elaborate equipment or set-ups.

Herein is presented a general strategy to perform reactions under mild to moderate CO2 pressures with dry ice. This technique obviates the need for ...

Negative Additive Manufacturing of Complex Shaped Boron Carbides

Boron carbide (B4C) is one of the hardest materials in existence. However, this attractive property also limits its machineability into complex shapes for high wear, high hardness, and lightweight material applications such as armors. To overcome this challenge, negative additive manufacturing (AM) is employed to produce complex geometries of boron carbides at various length scales. Negative AM first involves gelcasting a suspension into a 3D-printed plastic mold. The mold is then dissolved away, leaving behind a green body as a negative copy. Resorcinol-formaldehyde (RF) is used as a novel gelling agent because unlike traditional hydrogels, there is little to no shrinkage, which allows for extremely complex molds to be used. Furthermore, this gelling agent can be pyrolyzed to leave behind ~50 wt% carbon, which is a highly effective sintering aid for B4C. Due to this highly homogenous distribution of in situ carbon within the B4C matrix, less than 2% porosity can be achieved after sintering. This protocol highlights in detail the methodology for creating near fully dense boron carbide parts with highly complex geometries.

A method called negative additive manufacturing is used to produce near fully dense complex shaped boron carbide parts of various length scales. This technique is possible via the formulation of a novel suspension involving resorcinol-formaldehyde as a unique gelling agent that leaves behind a homogenous carbon sintering aid after pyrolysis.

Boron carbide (B4C) is one of the hardest materials in existence. However, this attractive property also limits its machineability into complex shapes for ...