Abstract
3-(3-butenyl)-5-[2-(1,3-dioxan-2-yl)ethyl]-2,4,4-trimethyl-2-cyclohexenone (13), containing the fully elaborated taxane A ring, was prepared from 4,4-dimethyl-2-cyclohexenone (43% for for four steps); two copper-catalyzed Grignard conjugate addition reactions on 4,4-dimethyl-2,5-cyclohexadienone (8) and 3-(3-butenyl)-2,4,4-trimethyl-2,5-cyclohexadienone (11) were employed as key transformations. Elaboration of (13) to the chloro keto acid 3-[3-(4-chloro-3-oxobutyl)-2,4,4-trimethyl-5-oxo-1(6)-cyclohexenyl]propanoic acid (6), was achieved via an epoxidation/regioselective chloride-mediated epoxide ring opening/Jones oxidation protocol (42% for three steps). Macrolactonization (59%) followed by chemoselective transannular aldol condensation within the resulting 11-membered bicyclic keto lactone 12,14,14-trimethyl-5-oxobicyclo[8.3.1]tetradeca-12-ene-3,6,11-trione (4), under thermodynamic control (51%), resulted in closure of the taxane B ring to afford the target 5-oxa-11,14,14-trimethyltricyclo[8.3.1.0 3 ,7]tetradeca-3(7),10-diene-4,12-dione (3) (2(5H)-furanone derivative)
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