Stereochemistry of the Cycloaddition of Singlet Excited β-Substituted Styrenes to Olefins

Abstract

The photocycloaddition of β-substituted styrenes (trans-cinnamic acid (1b), methyl trans-cinnamate (1c), trans-cinnamonitrile (1d), and cis-cinnamonitrile) to olefins occurs with retention of stereochemistry and involves the S1 state. In certain cases (1b, c) a photoene reaction competes with the cycloaddition. The triplet states of the β-substituted styrenes produced by sensitization give only [Formula: see text] isomerization. Neither cycloadduct nor photoene reaction is observed from the triplet states. It is thus likely that both addition and photoene reactions involve the S1 state of the β-substituted styrene.