摘要：

Thermal, photochemical, and photosensitized decompositions of 1,2-diphenyldiazopropane (1) have been shown to yield (Z)- and (E)-1,2-diphenylpropenes (4 and 5) and 1,1-diphenyl-1-propene (8) along with α-phenylpropiophenone (6), and its azine (7) in varying amounts depending on the conditions. The ratio of 4:5 was shown not to depend on the method of decomposition of 1 and had a value of 0.66 ± 0.2. The relative amounts of olefins 4 and 5, which result from hydrogen migration, and 8, which results from phenyl migration, varied with the mode of decomposition and with temperature. Thermal and photochemical decomposition of 2,2-diphenyldiazopropane (10) produced the same ratio of (Z)-/(E)-1,2-diphenylpropenes as from 1. These data are shown to be consistent with a mechanism involving production of the carbene (2) from diazo compound 1. The two carbene spin states, singlet and triplet, are postulated to be interconverting, and it is the singlet state which gives rise to hydrogen rearrangement while the triplet allows phenyl migration. The observation of two different carbenes (2 from 1 and 11 from 10) giving rise to the same olefin ratio (4/5) by migration of different groups argues for the existence of a discrete intermediate in the conversion of these carbenes (2 and 11) to olefins 4 and 5. It is suggested that this intermediate might best be formulated as the phantom singlet state (3) of α-methylstilbene. An additional study involving 1-(p-phenyl-d)-2-phenyldiazopropane (9) has reconfirmed the migratory aptitude sequence to a carbene center as H > Ph > CH3.

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