Generation of Stereochemically Defined Tetrasubstituted Enolborinates by 1,4-Hydroboration of α,β-Unsaturated Morpholine Carboxamides with (Diisopinocampheyl)borane

摘要

The enantioselective synthesis of acyclic all-carbon quaternary centers remains a significant challenge in organic synthesis. In view of the tremendous utility of enantioselective aldol reactions in organic synthesis, extension of this reaction to the enantioselective synthesis of all-carbon quaternary centers from stereochemically defined tetrasubstituted enolates would be highly valuable. However, attempts to generate such enolates or enolate equivalents by deprotonation of acyclic carbonyl compounds in most cases lead to geometric mixtures, which translates to poor diastereoselectivity in the subsequent aldol reaction.41 Thus, alternative methods for generation of acyclic tetrasubstituted enolates or their synthetic equivalents have been developed. Noteworthy among these, a highly stereoselective carbocupration of chiral ynamides followed by oxidation of the resultant vinylcuprate has been developed by Marek and co-workers.