Pergamon Tetrahedron: Asymmetry 11 (2000) 951–973 TETRAHEDRON: ASYMMETRY Studies towards the taxoid diterpene ABC-ring system: practical access to highly functionalized enantiomerically pure analogues of major group representatives † José Ignacio Martín Hernando, Maria del Rosario Rico Ferreira, José Ignacio Candela Lena, Nicolas Birlirakis and Siméon Arseniyadis * Institut de Chimie des Substances Naturelles, CNRS, F-91198 Gif-sur-Yvette, France Received 8 December 1999; accepted 14 December 1999 Abstract Short routes for practical syntheses of enantiopure taxoid subunits which possess oxygenation at sites appropriate for further elaboration into various members of the major taxoid families are described along with detailed structure elucidation. © 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction Although six total syntheses of taxol 1 have been reported, considerable effort continues to be devoted towards the development of more practical routes to conveniently access the taxoid diterpene framework. Recently, 2 we developed conditions for the four-step preparation of taxoid ABC diterpene framework 4a, in which the isophorone-derived racemic-1 was coupled in an A+C direction with the Hajos–Parrish ketone-derived (+)-2. 3 Starting from (±)-1 and (+)-2, key aldol precursor (-)-3 was produced in three steps. The published route to the key intermediate (-)-4a involves a transmetallation, as described by Still, 4 for the top-side linking of the left- and right-half segments, followed by a removal of TBS-protecting groups and a TPAP–NMO oxidation developed by Ley et al. 5 Intramolecular aldol 6 condensation converted the B-secotaxane 3 thus obtained to the target 4a.(S)-(+)-Hajos–Parrish ketone, whose absolute stereochemistry correlates correctly with the C-8 quaternary center of taxoids, was our departure point. This stereocenter controls the relative (and consequently the absolute) configuration of the remaining stereocenters. The ease of B-secotaxane construction and the successful C-1–C-2 linkage * Corresponding author. E-mail: simeon.arseniyadis@icsn.cnrs-gif.fr † We dedicate this article to Professor Pierre Potier on the occasion of his 65th birthday. 0957-4166/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0957-4166(99)00587-X tetasy 3221