Transposed Paterno-Buchi Reaction

A complementary strategy of utilizing pi pi* excited state of alkene instead of n pi* excited state of the carbonyl chromophore in a "transposed Paterno-Buchi" reaction is evaluated with atropisomeric enamides as the model system. Based on photophysical investigations, the nature of excited states and the reactive pathway was deciphered leading to atropselective reaction. This new concept of switching of excited state configuration should pave the way to control the stereochemical course of photoreaction due to the orbital approaches required for photochemical reactivity.