THE USE OF 4,4-DISUBSTITUTED NOPINONES FOR NATURAL-PRODUCT SYNTHESIS - SYNTHESIS OF ELEMANOID SESQUITERPENES

A general and convenient synthetic route to 4,4-disubstituted nopinones 14 from (+)-nopinone (1) is developed and applied to the asymmetric synthesis of some representative elemanoid sesquiterpenes. Phenylsulfenylation of 1 provided sulfide 6 in high yield. A convenient transformation of 6 to 3-(phenylsulfonyl)-4,4-disubstituted-nopinones 13 was accomplished by (i) m-CPBA oxidation of a sulfide compound followed by the Pummerer rearrangement and (ii) the conjugate addition of carbon nucleophiles to the resulting enones, 6 --> 8 --> 9 and 9 --> 10,11 --> 13. Subsequent reductive desulfurization of the adducts 13 provided 14 in good overall yield from 1. Bicyclic ketones 14 are envisioned as promising intermediates for natural product synthesis. As examples, syntheses of two elemanoid sesquiterpenes, beta-elemenone (16) and eleman-8-beta,12-olide (17) in optically active form from (1R,4S,5S)-4,6,6-trimethyl-4-vinylbicyclo[3.1.1]heptan-2-one (14a) were carried out.