CONTROL OF CARBENE REACTIVITY BY CRYSTALS - A HIGHLY SELECTIVE 1,2-H SHIFT IN THE SOLID-TO-SOLID REACTION OF 1-(4'-BIPHENYLYL)-2-PHENYLDIAZOPROPANE TO (Z)-1-(4'-BIPHENYLYL)-2-PHENYLPROPENE

Ruby red polycrystalline samples of 1-(4'-biphenylyl)-2-phenyldiazopro pane (la) efficiently transform into colorless (Z)-1-(4'-biphenylyl)-2 -phenylpropene [(Z)-3a] in up to 96% yield in a highly selective photo chemical solid-to-solid reaction. The solid state reaction was shown t o proceed via a carbene intermediate, and it was formulated asa 1,2-H shift with unprecedented stereoselectivity. It was shown that irradiat ion of la in inert solvents gives products via 1,2-H shifts [(Z)-3a an d (E)-3a] and 1,2-Ph migrations [(Z)-4a and (E)-4a] in yields that var y strongly with the polarity of solvent. Irradiation of la in ethanol gave similar products along with ethers 5a from insertion of the carbe ne into the EtO-H bond.