Photochemistry of Cyclopropene Derivatives. Intramolecular Hydrogen Transfer Reaction of Some 1-(Alkyl-substituted)cyclopropenes

Article abstract of DOI:10.1021/jo00253a008

The photochemical behavior of a number of 1-(alkyl-substituted)cyclopropenes that contain a hydrogen atom in the γ or δ position of the side chain has been studied in mechanistic detail.The triplet state, generated by sensitization techniques, undergoes hydrogen atom abstraction by a mechanism analogous to the Norrish type II process of carbonyl compounds.The quantum yield for the triplet-state hydrogen transfer reaction decreased substantially with deuterium substitution.The value of the isotope effect (k_H/k_D ca. 3.0) correlated well with related results in the literature indicating an early transition state for hydrogen transfer.The high regioselectivity of hydrogen transfer can be attributed to the stereoelectronic requirements for abstraction as well as the fact that the resulting diradical produced allows for maximum delocalization of the radical centers.