98. Enantioselective synthesis of (+)-α-allokainic acid by asymmetric lewis acid-mediated intramolecular ene reaction
    Oppolzer, W.; Robbiani, C.; Bättig, K.
    Tetrahedron 1984, 40, 1391-1400

-(+)-α-Allokainic acid ((+)-1) has been prepared for the ester of cis-β-chloroacrylic acid and (-)-8-phenylmenthol by a sequence of four synthetic operations. The crucial step8d→14d (Scheme 4) is a 1̃00%, diastereo- and 90% enantioselective intramolecular ene reaction proceeding at 35° on treatment of 8d with Me₂A1C1. Saponification of14d regenerated the auxiliary chiral alcohol and yielded (+)-1 on subsequent decarboxylation. In the analogous cyclization 11d→15d the sense of asymmetric induction (78% d.e.) was opposite as confirmed by the conversion of 15d to (-)-α-allokainic acid.

DOI : 10.1016/S0040-4020(01)82424-8