CYCLOPENTENYLLITHIUM ADDITIONS TO CHIRAL ALDEHYDES - DIASTEREOFACIAL SELECTIVITY INDICATING THE ABSENCE OF A PRONOUNCED NEIGHBORING CARBOXYLATE ANION EFFECT

The 1,2-addition of cyclopentenyllithium to a series of three five-membered aldehydo esters and their hemiacylals has been examined in order to assess the level and direction of facial selectivity surrounding nucleophilic attack at the aldehyde carbonyl and to clarify possible electronic and steric contributions stemming from neighboring functional groups. Neither methyl substitution of the acetic acid (ester) side chain nor the interchange of ester for carboxylate anion serve as important diastereocontrol elements. Instead, diastereofacial selectivity in these and related cyclic carboxaldehydes is governed by the inherent structural features of the ring system to which the functional group is attached. The convenient preparation of a complete subset of isomerically pure bicyclic lactones carrying five stereogenic centers is reported.