Stereoselective photocyclization to 2-aminocyclopropanols by photolysis of β-aminoketones and oxidative ring opening to enaminones

Article abstract of DOI:10.1016/S0040-4020(97)00459-6

Irradiation of β-aminopropiophenones 1 leads to the formation of 2-aminocyclopropanols 2 which can undergo oxidative ring opening to give enaminones 3. The regioselectivity of cyclopropanol formation of the α-benzyl substituted 1 is determined by the preferred charge transfer interaction between the photoexcited benzoyl chromophore and the amino group. The photocyclizations of the α- or β-substituted 1 proceed stereoselectively. No photoracemization of the pure enantiomers of 1m, independent of the solvent polarity was observed. Aryl or alkyl substituents at the C(3)- or C(2)-ring atom stabilize the cyclopropanol derivatives. The formation of 3 indicates regioselective C(1)-C(2) ring opening of 2 probably by localization of the excitation energy.