The cyclopropantion reaction conditions were optimized. The one-pot approach was used to avoid the existence of high concentration of ylide, and Solid-Liquid phase transfer system was used to reduce the concentration of the base in the solution. It was found that a variety of α,β-unsaturated esters, amides, ketones and nitriles are all worked well to afford the cyclopropanation products in good yields. The trans/cis selectivities are excellent with the β-hydrogen or β-aryl substrates, while the selectivity is good with β-alkyl substrate. All reaction’s ee is higher than 92%, and up to 99%.
Several stereo-isomers of the sulfonium salt were also investigated. It was found that the endo-type sulfonium salts were also worked but afforded the corresponding cyclopropanes with opposite absolute configuration compared with that from the exo-type salt.
Based on the crystal structure of sulfonium salt and the reaction results, it was proposed that the β-hydroxy of the sulfonium salt play a key role in the highly stereoselective cyclopropantion reation.
Thus, we have developed an efficient method for one-step enantioselective synthesis of 1,3-disubsituted-2-silylvinylcyclopropanes. As a result, both diastereoselectivity(cis/trans) and enantioselectivity are excellent in most cases studied. Since the ylide is readily available from cheap D-camphor and the enantioselectivity is partially tunable, the current method has a high potential for practical use in organic synthesis.
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