Z-Stereoselective Aza-Peterson Olefinations with Bis(trimethylsilane) Reagents and Sulfinyl Imines

Highly stereoselective aza-Peterson olefinations from bench-stable alpha,alpha-bis(trimethylsilyl)toluene reagents and N-substituted imines have been achieved using TMSO-/Bu4N+ as Lewis base activator in THF. Remarkably, and for the first time, N-t-butanesulfinyl imines were utilized for the synthesis of Z-stilbenes with excellent selectivities, while N-aryl imines generated E-stilbenes under identical reaction conditions. The protocol proved general for numerous examples with low molecular weight byproducts formed. The origin of the Z-selectivity is proposed to be a result of diastereoselective addition to N-t-butanesulfinyl imines followed by syn-elimination of an in situ formed hypervalent silicate.