The Renaissance of Zinc Carbenoid in Stereoselective Synthesis in Acyclic Systems

In the last few decades we have witnessed the renaissance of zinc carbenoid in acyclic stereoselective synthesis. From the pioneering work of Simmons and Smith that led to a myriad of beautiful enantioselective cyclopropanations of alkenes, zinc carbenoid is again at the center of interest, but this time for the acyclic control of selectivity in allylation reactions. A straightforward method, utilizing the dual characteristics of zinc carbenoid serving both as an electrophile and as a nucleophile, has been recently developed for the preparation of various 3,3-disubstituted allylzinc species that react with various carbonyl and imine moieties to give homoallyl alcohols and amines, respectively, with very high diastereoselectivity. In a one-pot operation, three new carbon–carbon bonds as well as two new sp3 stereogenic centers were formed, including the formation of the challenging all-carbon quaternary stereogenic centers.