P. Jones, S. Ley, N. Simpkins
1986
Citations
0
Influential Citations
54
Citations
Journal
Tetrahedron
Abstract
Abstract The first total synthesis of the diterpene clerodane insect antifeedant ajugarin I (1) has been achieved. The key step of the synthesis discloses the use of the 1,3-dithiolane unit to stereochemically direct the conjugate addition of a but-3-enyl cuprate to set in place the C-10 sp3 carbon centre. The trans -fused ring geometry was obtained by conjugate additon of a vinyl cuprate to an enone and regio and stereoselectively trapping the resulting enolate with formaldehyde. Introduction of the necessary butenolide side chain was achieved by conjugate addition of a sulphone stabilised anion to ethyl-4-(t-butyldimethylsilyloxy) but-Z-ynoate followed by work-up with fluoride. Final hydroxyl directed epoxidation was not specific giving both the natural product ajugarin I and its 4-epi isomer. Chemical modification of the insect antifeedant clerodin hemiacetal afforded a series of side chain modified structures for biological evaluation.