Carbazoles Smith carbazole synthesis

The first efficient synthetic strategy for 2,7-functionalized carbazoles was reported by Smith and Brown in 1951 [21,22], The crucial step in this synthesis is the formation of the azide compound generally starting from an... 

As we saw with the early work of Smith and others, the pyrolysis of ortfto-azidobiphenyls is a powerful route to carbazoles. A recent synthesis of 2,7-dinitrocarbazole... 

Scheme 17 The Smith Synthesis of Carbazoles from 2-Azidobiphenyls...

In 1951, Smith and Brown were the first to show that the photolysis of aryl azides led to carbazoles (Scheme 17, equation 1) [114], a reaction that also occurs upon heating. Other carbazoles so prepared are 36 to 39. This reaction has been reviewed [115-119], and has been of more interest mechanistically than synthetically, by the groups of Reiser [120, 121], Swenton [122-124], Berry [125], Sundberg [126, 127], Yabe [128-130], Meth-Cohn [131], and Spagnolo [132]. Sundberg provides an excellent summary of the possible mechanisms involved in the photolysis of 2-azidobiphenyl to carbazole [126, 127], and his own work indicates that a triplet nitrene may not be the sole or major carbazole precursor [127]. In any event, the photochemical transformation of aryl azides is a useful synthesis of carbazoles. Some additional examples are shown in Scheme 17 [114, 115, 124, 128, 129, 133]. In addition, Sauer and Engels obtained, as expected, a nearly 1 1 ratio of 1- and 3-methylcarbazoles (85%) on photolysis of 2-azido-3 -methylbiphenyl [134]. 

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