Asymmetric endoselective [4+2] heterocycloadditions of styrene dienophiles with chiral benzylidenepyruvic esters. Total synthesis of (-)-O-dimethylsugiresinol

Article abstract of DOI:10.1016/S0040-4039(97)00144-5

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 diastereoselective ratios (from 58/42 to 86/14). Interestingly, the benzylidenepyruvic esters 8g and 8h, deriving from a new chiral vector, the α-O-silyl ether 6 of (D)-(-)-erythronolactone 5, gave the corresponding endo adducts 9g and 9h with a high diastereoselective ratio (dr ≤95/5). The adduct 9h was used as a precursor in a five-step synthesis of 'natural' (-)-dimethylsugiresinol (1b).