SYNTHESIS AND PHOTOCHEMICAL DECOMPOSITION OF PYRAZOLINES FROM HOMOCHIRAL AMINO PENTENOATES - A LASER FLASH-PHOTOLYSIS STUDY

Optically pure pyrazolines have been synthesized by cycloaddition of d iazomethane to homochiral amino pentenoates, facial diastereoselectivi ty being the opposite depending on the Z/E stereochemistry of the prec ursors. 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 i nfluence of sensitizers. The transient behaviour of the pyrazoline tri plet state has been analyzed by laser flash photolysis either after di rect excitation or after energy transfer from benzophenone. (C) 1997 E lsevier Science Ltd.