Synthèse asymétrique et configuration absolue de dihydropyranes substitués, par hétérocycloaddition intermoléculaire d'éthers vinyliques chiraux
摘要:
The alkyl vinyl ethers 2b-8b (deriving from the alcohols 2a-8a) smoothly reacted with methyl E-benzylidenepyruvate 10 in the presence of catalytic amounts of Eu(fod)(3) or Yb(fod)(3) in refluxing hexane, thus leading to the dihydropyran endo adducts 13-19 in high yields (80-95%). The endo-cycloadducts 13-17 were obtained with diastereofacial selectivities (ds) ranging from 76/24 to 87.5/12.5. Asymmetric induction was found to culminate with the vinyl ether (-)-7b deriving from n-butyl (R)-(-)-mandelate : the best ds (92.5/7.5) was obtained for the corresponding adduct 18 after 6 days at room temperature. The absolute configurations of the major isomers of the dihydropyrans 16-18, 20 and 21 were established by oxydative degradation to optically active alpha-phenylsuccinic acid derivatives.
Chiral enol ethers in carbohydrate chemistry: De novo synthesis of protected L-2-deoxy hexoses
作者:Gilles Dujardin、Sandrine Rossignol、Eric Brown
DOI:10.1016/0040-4039(96)00769-1
日期:1996.6
(3,4,6)Tri- and (3,4,)-di-O-benzyl-2-deoxy-L-glucose 8 and 12 have been denovo synthesized in a convergent seven-step sequence involving asymmtric endo heterocycloaddition of the new heterodiene, methyl (E)-benzyloxylmethylene pyruvate 2b with the O-vinyl mandelic ester (R)-(−)-3.
An Improved Dienophile-Induced Access to Enantiopure 2,4-Dideoxysugar Lactones via Hetero Diels-Alder Reaction: Synthesis of the (+)-Lactone Moiety of Compactin