DIASTEREOSELECTIVITY IN ORGANOMETALLIC ADDITIONS TO THE CARBONYL GROUP OF PROTECTED ERYTHRULOSE DERIVATIVES

We have investigated a number of nucleophillic additions to L-erythrul ose derivatives (4-12) bearing protective O-silyl, O-benzyl, and O-tri tyl groups in various relative positions. The results are discussed in the frame of chelated vs nonchelated transition states with additiona l support of previously published theoretical calculations. Sound evid ence appears to exist for the formation of alpha-chelates as the key i ntermediates in nucleophillic additions to these alpha,beta-dioxygenat ed ketones. Since such evidence is still lacking in the case of beta-c helates, proposals of their intermediacy have been relegated in favor of the more solid Felkin-Anh model, which predicts the same stereochem ical result. The behavior of these highly functionalized ketones does not always match that of structurally similar aldehydes.