Synthesis and photochemical decomposition of pyrazolines from homochiral amino pentenoates. A laser flash-photolysis study

Optically pure pyrazolines have been synthesized by cycloaddition of diazomethane to homochiral amino pentenoates, facial diastereoselectivity being the opposite depending on the Z/E stereochemistry of the precursors. Photo-decomposition of these pyrazolines to the corresponding cyclopropanes has been shown to occur stereospecifically and has been studied in order to find the optimal conditions and to establish the influence of sensitizers. The transient behaviour of the pyrazoline triplet state has been analyzed by laser flash photolysis either after direct excitation or after energy transfer from benzophenone.