Chiral dienolate chemistry in remote asymmetric induction: the allylation / cope rearrangement sequence leading to γ-chiral α, β-unsaturated acid derivatives
allylation of the dienolate derived from the chiral α, β- or β, γ-unsaturated imidefollowed by the Cope rearrangement is shown to effect the net remote asymmetricinduction to create a new chirality of either configuration at the γ-position in high % de. The utility of this approach is shown in the asymmetric synthesis of the C6 side chain of Zaragozic acid A.
An optically pure C-6 O-acyl side chain equivalent of zaragozic acid A, (2E, 4S, 6S)-4, 6-dimethyl-2-octenoic acid, which features a 1, 3-syn-dimethyl-substituted carbon chain, has been readily synthesized from (S)-2-methylbutanal using a combination of the Evans aldol reaction and the Ireland deoxygenation method.