in 34% overall yield via chemoselective cross metathesis of
8 and 10, followed by removal of the N-Boc group and
cyclization of the intermediate amino dienoate via intramolecular
1,6-conjugate addition. Subsequent protection of 15
as its trifluoroacetamide derivative afforded 3.
5a Spectral data
of 3 were consistent with those reported by Kibayashi.9
Inasmuch as 3 had been previously converted into pinnaic
acid (1) by Danishefsky,5b the preparation of 3 in 11 steps
(5.8% overall yield) starting from commercially available
methyl 1-cyclopentene-1-carboxylate completes a formal
synthesis of 1.