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-Schu ster reaction or by introduction of a vinyl group with vinylcerium dic hloride 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-dio l unit with the correct relative stereochemistry. Closure of the B-rin g is brought about in excellent yield by displacement of an allylic br omide at C9 by an alpha-sulfonyl anion at C10. (C) 1997 Elsevier Scien ce Ltd.