Lignans .19. Total synthesis of (-)-O-dimethylsugiresinol, involving asymmetric [4+2] heterocycloaddition of a styrene with a benzylidenepyruvic ester of an alpha-O-silyl derivative of (D)-erythronolactone

alpha-O-t-Butyldiphenylsilyl-(D)-erythronolactone [(+/-)-25] (a new chiral vector) was esterified with 4-methoxybenzylidene pyruvic acid (19). Eu(fod)(3) catalyzed [4+2] heterocycloaddition of the latter 1-oxabutadiene with 4-methoxystyrene (as the dienophile), afforded high yields of the endo adduct 23c with 95/5 diastereofacial ratio. Five further steps led to enantiomerically pure natural (-)-O-dimethylsugiresinol (-)-2 in 12% overall yield from the acid 19. (C) 1997 Elsevier Science Ltd.