Diazoacetophenone, photolysis

The yields of cyclopropanes in this case are low in relation to the amount of acetophenone formed. However, similar cyclopropane product ratios are obtained when photolysis is carried out in the presence of Michler s ketone as sensitizer. Thus the carbene intermediate produced in the direct irradiation is thought to be a triplet, as suggested by the nonstereospecificity of its addition. Whether this intermediate arose from singlet diazoacetophenone (via singlet decomposition and intersystem crossing of the singlet carbene) or by decomposition of the triplet molecule was not determined. 

By Cu-catalyzed decomposition of ortho-seleno- and -telluro-substituted oj-diazoacetophenones, Lohner and Praefcke 482 synthesized seleno- and telluro-3-coumaranones 483. This reaction with the participation of a free carbene generated by photolysis of 482 (Z = Te) gives unsatisfactory results (80JOM173). 

The large variety of products related to photolysis and thermal dediazoniations of diazo ketones is documented in a recent investigation of Padwa et al. (1993 b) of alk-2-enyl- and alk-2-ynyl-substituted a-diazoacetophenones. Thus, the photolysis of a-diazo-2-ethenylacetophenone (8.69) resulted in the formation of 2-naphthol (8-37,... 

Lewis acids efficiently catalyze the transfer of diazoketones and diazoesters to amides and nitriles to furnish 2,4,5-trisubstimted oxazoles (Scheme 1.49). In particular, Eguchi and co-workers found that BF3 OEt2 was the best catalyst for reaction of the adamantyl diazoketoester 180 with acetonitrile. Attempts to prepare 181 using Rh(II)acetate or photolysis were unsuccessful. Similarly, Ibata and Isogami °° described a general synthesis of 5-aryl-2-(chloromethyl)oxazoles 183 from a BF3.0Et2-catalyzed addition of a-diazoacetophenones 182 with chloro-acetonitrile. The yields were quite respectable (Table 1.12). 

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