Graebe-Ullmann carbazole-carboline synthesis

The Graebe-Ullmann reaction of Af-arylbenzotriazoles is an extraordinarily versatile and powerful synthesis of carbazoles and carbolines. Despite the commonly encountered low yields, the ease of preparation of the requisite Al-arylbenzotriazoles, either by the diazotization of 2-ami-nodiarylamines or the coupling of benzotriazole with the appropriate aromatic or heteroaromatic partner, elevates the Graebe-Ullmann reaction to one of distinction for the synthesis of carbazoles and carbolines. 

The Graebe-Ullmann synthesis, converts 1-arylbenzotriazoles into carbazoles or their heterocyclic analogs. It has been accelerated under microwave irradiation, where the l-(4-pyridyl)-benzotriazole was converted into a y-carboline (Molina et al, 1993). This synthesis was completed within 2.5 h by conventional method while it takes only 15 min under microwave exposure and the yield was also increased. 

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