Kurt Bättig

A total synthesis of (±)-isocomene and (±) β-isocomene by an intramolecular ene reaction

Abstract The racemic sesquiterpenes isocomene 1 and β-isocomene 22 have been synthesized starting from 1,7-octadien-3-one 10 in a stereoselective manner. In the key step 12 → 13 (Scheme 5) the C-7, C-8-bond was formed by an intramolecular thermal ene reaction. Further transformations of 13 (Scheme 6) involved successively ring contraction 18 → 19 , elimination 21 → 22 and olefin isomerization 22 → 1.

Total synthesis of (±)-Δ9(12)-capnellene via iterative intramolecular type-I-“Magnesium-ene” reactions

The marine triquinane sesquiterpene Δ9(12)-capnellene (1) was synthesised from 2,2,5-trimethyl-5-hexenal (2) by a sequence of all synthetic operations in 5% overall yield. The key steps 3 → 4 → 5 → 6 involve two intramolecular type-I-“Mg-ene” processes.

Enantioselective synthesis of (+)-α-allokainic acid by asymmetric Lewis acid-mediated intramolecular ene reaction

Abstract -(+)-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 step 8d→14d (Scheme 4) is a 100%, diastereo- and 90% enantioselective intramolecular ene reaction proceeding at 35° on treatment of 8d with Me2A1C1. Saponification of 14d 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.