M. Kato, Masataka Watanabe, B. Z. Awen
Sep 1, 1993
Citations
0
Influential Citations
9
Citations
Journal
Journal of Organic Chemistry
Abstract
(1R,5S)-4-Ethyl-6,6-dimethyl-3-(phenysulfonyl)bicyclo[3.1.1]kept-3-en-2-one (i) was prepared from (+)-nopinone (1) in six steps and 70% overall yield via (1R,5R)-6,6-dimethyl-3-(phenylthio)bicyclo-[3.1.1]hept-3-en-2-one (2). Alkylation reactions of 7 with alkyl bromides 16 (a, alkyl; b, 3-methyl-2-butenyl; c, propargyl; d, benzyl bromide) in the presence of K 2 CO 3 in MeCN proceeded in regio- and extracyclic stereocontrolled fashion to give, as the major product, mixtures of γ-alkylated products 17a-d possessing a new chiral center of R configuration adjacent to a ring and 18a-d possessing that of S configuration, whose ratios are 17a-18a, 10:1, 17b-18b, 7:1; 17c-18c, 13:1; and 17d-18d, 18:1, along with α-alkylated products 19a-d and O-alkylated product 20a,b on reactions with 16a,b. In the appplication of 17 as the synthetic intermediate for the asymmetric synthesis, starting with (1R,5S)-6,6-dimethyl-4-[(1R)-1-methyl-3-butenyl]-3-(phenylsulfonyl)bicyclo[3.1.1]hept-3-en-2-one (17a), (-)kanshone A (8), a nardosinane sesquiterpene, was synthesized in a highly stereoselective fashion in 12 steps via (1R,4R,5R)-4,6,6-trimethyl-4-[(1R)-1-methyl-3-butenyl] bicyclo[3.1.1]heptan-2-one (30) and its cyclobutane-ring opening product, (4S,4aR,5R)-1-acetoxy-4-isopropenyl-4a,5-dimethyl-3,4,4a,5,6,7-hexahydronaphthalene