A CYCLOADDITION APPROACH TO BREYNOLIDE

A novel approach to the functionalized hydrobenzothiophene subunit of the sesquiterpene breynolide (3) has been developed. The sequence feat ures the Diels-Alder reaction of the vinyl sulfones 12 and 13 with the Danishefsky diene 9 to give the cycloadducts 14 and 16 as the major p roducts. Reduction of the sulfone moieties of 14 and 16 gave the sulfi des 20 and 21, respectively. Subsequent dipolar cycloaddition of 20 an d 21 with a functionalized nitrile oxide gave the corresponding adduct s 24 and 25, which possess functionality suitable for elaboration into breynolide (3). (C) 1997 Elsevier Science Ltd.