Stereoselective synthesis of alcohols, XXXIV. Towards an understanding of cram/anti‐cram selectivity on addition of crotylboronates to α‐methylbutyraldehyde

The diastereoselectivity on addition of γ‐substituted allylboronates to α‐methylbutyraldehyde (9) did not depend on the size of the substitutent in the reagent, but only on its location in the Z or E position. This finding required a reinterpretation of the reasons for the attendant reversal in diastereoselectivity. New hypotheses are presented based on force‐field calculations on model structures for the transition states.