Name: chemoselective preparation of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes based on the oxidative iodination of terminal alkynes
Uploaded: 2018-09-12T14:45:00
Description: Watch this Scientific Journal Video about Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes at JoVE.com

This work was supported by the National Nature Science Foundation of China (21502023).

1. Synthesis of 1-(Iodoethynyl)-4-Methylbenzene (2, 1-Iodoalkynes)
<ol>
	<li>Add 133 mg (0.36 mmol) of TBAI and 3 mL of CH3CN to a reaction tube that contains a magnetic stirring bar, which is open to air. Then, add 38 &#956;L (0.3 mmol) of p-tolylethyne to the mixture using a microsyringe.</li>
	<li>Add 96.6 mg (0.3 mmol) of PIDA to the vigorously stirred reaction mixture in 10 portions over a period of 20 min using a spatula.</li>
	<li>Stir the reaction mixture at room temperature for 3 h...

1-Iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes can be chemoselectively synthesized using hypervalent-iodine reagents as efficient mediators for oxidative iodination(s). The most critical factors of these chemoselective iodination protocols are the nature and loading of the iodine source, as well as the solvent. For example, 1-iodoalkyne 2 was obtained as the major product (52% yield) when TBAI (2.5 equiv loading) was selected as the iodine source in combination with MeOH as the solvent (<stro...

Iodoalkynes and iodoalkenes are widely used important precursors and building blocks in organic synthesis1,2,3,4, biologically active substances, and useful in the synthesis of materials and complex molecules given the ease of converting the C-I bond5,6,7,8. In recent years, the oxidative iodination of terminal alkynes has attracted more attention to the synthesis of iodoalkyne and iodoalkene derivatives. So far, efficient methods that use metal catalysts9,10,11,12, hypervalent-iodonium catalysts13,14, an anodic oxidation system15, ionic liquid systems16, KI (or I2)-oxidant combinations17,18,19,20, ultrasound21, phase-transfer catalysts22, N-iodosuccinimide9,22,23,24,25, n-BuLi26,27,28,29,30,31, Grignard reagents32, and morpholine catalysts17,33,24,35&#160;have been developed for the iodination of alkynes. Recently, we have reported a practical and chemoselective protocol for the synthesis of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes36. The features of this method are green and practical: (1) the toxicity of hypervalent-iodine catalysts as oxidative functionalization reagents is low compared to other conventional heavy-metal-based oxidants37,38,39,40,41,42, and (2) TBAI and/or KI are used as iodine sources. In addition, our system affords excellent selectivity under mild conditions. The chemoselective synthesis of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes requires precise control over various factors, including the composition, the oxidant, the iodine source, and the solvent. Among these, the iodine source is the most important factor for the chemoselectivity of the reaction. After the screening of several types and loadings of the iodine source as well as the solvents, three methods were identified and established. Firstly, TBAI as an iodine source in combination with PIDA (TBAI-PIDA) is selective for the synthesis of 1-iodoalkynes. Alternatively, 1,2-diiodoalkenes are efficiently obtained using a KI-PIDA system. Both methods afford the corresponding products in high yield and high chemoselectivity. The corresponding tri-iodinationproducts, i.e., 1,1,2-triiodoalkenes, were obtained in good yield from the one-pot synthesis that combine the TBAI-PIDA and KI-PIDA systems36.
Here, we will demonstrate how the chemoselectivity for the iodination of terminal alkynes can be steered from 1-iodoalkynes to 1,2-diiodoalkenes and to 1,1,2-triiodoalkenes under similar reaction conditions, highlighting the precise control that can be exerted by judiciously choosing oxidant, iodine source, and solvent. For the development of this new synthetic technique, p-tolylethyne was used as a model substrate. Although the following protocols focus on the synthesis of 1-(iodoethynyl)-4-methylbenzene, (E)-1-(1,2-diiodovinyl)-4-methylbenzene, and 1-methyl-4-(1,2,2-triiodovinyl)benzene, these compounds are representative for 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes, respectively, i.e., the protocols are broad in scope, and the same techniques can be applied to the chemoselective iodination of aromatic and aliphatic terminal alkynes36.
Reagents employed in the chemoselective iodination of terminal alkynes and small deviations from the techniques described result in dramatic differences with respect to the target products. For instance, changing of iodine source from TBAI to KI and changing of solvent from CH3CN to a CH3CN-H2O has a dramatic impact on the chemoselectivity of the iodination. The detailed protocol aims at helping new practitioners in the field with the chemoselective iodination of terminal alkynes to avoid many common pitfalls during the synthesis of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes.

<table border="0" cellpadding="0" cellspacing="0" width="860">
	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">4-ethynyltoluene,98%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">D080006</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">phenylacetylene,98%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">W330041</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">1-ethynyl-4-methoxybenzene,98%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">D080007</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">1-ethynyl-4-fluorobenzene,98%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">D080005</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:263px;">4-(Trifluoromethyl)phenylacetylene,98%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">W320273</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:263px;">4-Ethynylbenzoic acid methyl ester,97%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">A020720</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">3-Aminophenylacetylene,97%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">D080001</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">3-Butyn-1-ol,98%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">A040031</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">Propargylacetate,98%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">L10031</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">Tetrabutylammonium Iodide,98%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">E010070</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">Potassium iodide,98%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">E010364</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:263px;">(diacetoxyiodo)benzene,99%</td>
			<td style="width:311px;">Energy Chemical</td>
			<td style="width:119px;">A020180</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">acetonitrile, HPLC grade</td>
			<td style="width:311px;">fischer</td>
			<td style="width:119px;">A998-4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">magnetic stirrer</td>
			<td style="width:311px;">IKA</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">rotary evaporator</td>
			<td style="width:311px;">Buchi</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:263px;">Bruker AVANCE III 400 MHz Superconducting Fourier</td>
			<td style="width:311px;">Bruker</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:263px;">High-performance liquid chromatography</td>
			<td style="width:311px;">Shimadzu</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

chemoselective preparation of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes based on the oxidative iodination of terminal alkynes

We present the chemoselective synthesis of 1-(iodoethynyl)-4-methylbenzene, 1-(1,2-diiodovinyl)-4-methylbenzene, and 1-methyl-4-(1,2,2-triiodovinyl)benzene as representative examples for the practical chemoselective preparation of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes from the chemoselective iodination of terminal alkynes mediated by hypervalent-iodine reagents. The chemoselectivity was confirmed by using p-tolylethyne as a model substrate to screen a variety of iodine sources and/or the hypervalent-iodine reagents. A combination of tetrabutylammonium iodide (TBAI) and (diacetoxyiodo)benzene (PIDA) selectively generates 1-iodoalkynes, while a combination of KI and PIDA generates 1,2-diiodoalkenes. A one-pot synthesis based on both TBAI-PIDA and KI-PIDA yields the corresponding 1,1,2-triiodoalkenes. These protocols were subsequently applied to the synthesis of synthetically important aromatic and aliphatic 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes, which were obtained in good yield with excellent chemoselectivity.

The chemoselective synthesis of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes based on the oxidative iodination of p-tolylethyne is summarized in Figure 1. All reactions were exposed to air. All compounds in this study were characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and HPLC to access the structure of the product and the selectivity of the reaction, as well as to explore the purity. The obtained products ar...

Watch this Scientific Journal Video about Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes at JoVE.com

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

Herein, detailed protocols for the oxidative iodination of terminal alkynes using hypervalent-iodine reagents are presented, which chemoselectively afford 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes.

We present the chemoselective synthesis of 1-(iodoethynyl)-4-methylbenzene, 1-(1,2-diiodovinyl)-4-methylbenzene, and ...

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