ASYMMETRIC ENDOSELECTIVE [4- TOTAL SYNTHESIS OF (-)-O-DIMETHYLSUGIRESINOL(2]HETEROCYCLOADDITIONS OF STYRENE DIENOPHILES WITH CHIRAL BENZYLIDENEPYRUVIC ESTERS )

Eu(fod)(3) catalyzed [4+2] heterocycloadditions of para-methoxystyrene 7 with esters 8a-f of benzylidenepyruvic acids (deriving from various chiral alcohols) furnished endo adducts 9a-f with variable diastereos elective ratios (from 58/42 to 86/14). Interestingly, the benzylidenep yruvic esters 8g and 8h, deriving from a, new chiral vector, the alpha -O-silyl ether 6 of (D)-(-)-erythronolactone 5, gave the corresponding endo adducts 9g and 9h with a high diastereoselective ratio (dr great er than or equal to 95/5). The adduct 9h was used as a precursor in a five-step synthesis of ''natural'' (-)-dimethylsugiresinol (1b). (C) 1 997 Published by Elsevier Science Ltd.