Stereocontrol in allylboration reactions

Abstract

Crotyl-boronates add to aldehydes with high simple diastereoselection, such that E-crotyl-boronates give anti-homoallvl alcohols, and Z-crotyl-boronates their syn-counterparts. This reaction has been extended to stereoselective ring closure reactions by intramolecular allylboration. Moreover, by using suitably substituted crotyl boronates homoallyl alcohols having quarternary stereogenic carbon centers have been obtained with good diastereoselection. The development of chiral crotyl boronate reagents, having an additional stereogenic center o to the boron atom, allowed reactions with aldehydes to be accomplished with full transfer of chirality; i.e. control of the absolute configuration of the products. © 1990, IUPAC.