Dienophilie des olefines captodatives - VI 1 syntheses et cycloadditions de diels-alder des α-alkylthio-acrylates d'alkyle avec le cyclopentadine : influence des facteurs steriquis sur la reactivite et sur la stereoselectivite

Abstract

The Diels-Alder reactions of cyclopentadiene with a series of four α-alkylthio-alkyl acrylates were investigated. Although slightly slower than the reactions of unsubstituted alkyl acrylates, the spontaneous cycloadditions of these captodative olefins occur at room temperature affording adducts in excellent yield. The steric effect of the ester function is found to be more important in determining the dienophilic reactivity than the endo/exo ratios of the adducts and increase in the size of the alkylthio group reduces the endo selectivity of that group from 66–69% (for methylthio) to 25–22% (for tertiobutylthio group). The aluminium trichloride complexed methoxycarbonyl group leads to a very high endo-stereoselectivity (97%) of that group.