Synthesis of the taxol AB-system by olefination of an A-ring C1 ketone and direct B-ring closure

Two syntheses of 13-deoxy-taxol C1 ketones are presented. Olefination of these C1 ketones is achieved, indirectly, via either the Meyer-Schuster reaction or by introduction of a vinyl group with vinylcerium dichloride followed by allylic rearrangement. Both methods provide the E-olefin exclusively. Dihydroxylation of these olefins is achieved with catalytic OsO4 and NMNO in moderate yield, providing the taxol-1,2-diol unit with the correct relative stereochemistry. Closure of the B-ring is brought about in excellent yield by displacement of an allylic bromide at C9 by an alpha-sulfonyl anion at C10. (C) 1997 Elsevier Science Ltd.