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.
Enantioselective [4 + 2] Cycloadditions of <i>o</i>-Quinone Methides: Total Synthesis of (+)-Mimosifoliol and Formal Synthesis of (+)-Tolterodine
作者:Carolyn Selenski、Thomas R. R. Pettus
DOI:10.1021/jo048703c
日期:2004.12.1
The first example of an enantioselectivecycloaddition of an o-quinone methide (o-QM) with a chiral enol ether is described along with the total synthesis of (+)-mimosifoliol and the formal synthesis of (+)-tolterodine. These syntheses exemplify a three-component, one-pot benzopyran approach for the construction of chiral benzylic junctions. Cycloadditions of various enol ethers and o-QMs are examined