Carbazoles, synthesis from azides

The most reliable method for generating nitrenes is the thermal or photochemical elimination of nitrogen from azides. An alternative method which is useful for indole and carbazole synthesis is the deoxygenation of aromatic nitro compounds with trivalent phosphorus compounds. Triethyl phosphite is the most commonly used reagent, though more reactive compounds may be useful in special cases (B-79MI30600). 

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... 

The preparation of an indole (nitrene generated from an azide - the Hemetsberger-Knittel synthesis) and of carbazole ° (nitrene generated by deoxygenation of a nitro group) illustrate the power of the method. 

A key step in a synthesis of the carbazole alkaloid murraya-quinone-B (132) is the concomitant indole ring formation and regio-selective Claisen rearrangement from the azide (129), which on... 

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