Lignans.19. Total synthesis of (−)-O-dimethylsugiresinol, involving asymmetric [4+2] heterocycloaddition of a styrene with a benzylidenepyruvic ester of an α-O-silyl derivative of (D)-erythronolactone
作者:Eric Brown、Gilles Dujardin、Mickaël Maudet
DOI:10.1016/s0040-4020(97)00646-7
日期:1997.7
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.
Asymmetric endoselective [4+2] heterocycloadditions of styrene dienophiles with chiral benzylidenepyruvic esters. Total synthesis of (−)-O-dimethylsugiresinol
作者:Gilles Dujardin、Mickaël Maudet、Eric Brown
DOI:10.1016/s0040-4039(97)00144-5
日期:1997.3
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 to ). 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