The elaboration of the ring A aldehydes 1, 7, and 11 into more highly functionalized intermediates for taxoid synthesis is described. An improved route to the triene 4 and the adduct 28b is reported. Additional condensations of selected aldehydes (1,7) with the organolithium reagents derived from the substituted halodienes 8 and 14 afforded the allylic alcohols 10 and 15 with a diastereoselectivity of ~5:1. Further manipulation of these products by the installation of an α-keto-acetylenic dienophile provided a taxoid precursor with the C2, C9, C10, C13, and C20 oxygens installed in the case of 23 (from 7), and the less functionalized systems 27 and 27a (from 1). Keywords: taxoid, paclitaxel, Diels–Alder, cyclohexene, dienes.
The syntheses of a series of oxygenated cyclohexene ring A synthohs 20, 22–27, 34, 36, and 37 that possess suitable functionality for further elaboration for taxoid synthesis are described. These compounds have been prepared from β-ionone by a series of oxidative and addition reactions or alternatively by Lewis acid catalyzed Diels–Alder cycloadditions with the oxygen-containing trimethyl substituted dienes 31 and 33. Keywords: taxoid, paclitaxel, dienes, Diels–Alder, β-ionone.