Highly stereoselective ylide aziridination of N-sulfonylimines with sulfonium propargylides:: A simple way to synthesize scalemic acetylenylaziridines

Under phase-transfer or low-temperature conditions, the ylide generated from diphenylsulfonium salt 2 readily reacts with N-sulfonylimines 1 to give acetylenylaziridines in excellent yields, but low to moderate cis/trans selectivity. When using n-BuLi as the base to generate the ylide at low termperature, product 3 with an intact silyl protecting group is obtained. t-BuOK, however, leads to desilylation product 4. With Cs2CO3 as the base, dimethylsulfonium salts 6, 21, and 22 show much better cis/trans selectivity (>98:2) than diphenylsulfonium salt 2. The asymmetric version of the above aziridination reaction using camphor-derived sulfonium salts 12-14 and 20 gives chiral aziridines with ee values up to 85%. Both (2R,3S)-(-)-3 and (2S,3R)-(+)-3 can be prepared from 12/20 or 13/14, respectively. Ylides produced from telluronium salt 7 failed to react with imine la at room temperature, but the reaction succeeded at low temperature. Arsonium ylides from 8 cannot react with N-sulfonylimines under both sets of conditions.