Synthesis by construction of the second heterocyclic ring on to an existing heterocycle

1 Synthesis by construction of the second heterocyclic ring on to an existing heterocycle 

Pyrolysis of an azide frequently produces the reactive nitrene, which immediately attacks a nearby position on an adjacent ring. The azide is usually heated in an inert high-boiling solvent, although cyclization may occur without a solvent. Photochemically induced cyclization of an azide can often give a good yield of product. 

Thermal decomposition of 3-azido-2,2 -bithienyl (284) and 3-azido-2,3 -bithienyl (285) gave 4H-dithieno[3,2-Z 2, 3 -d]pyrrole (286) and 4//-dithieno[2,3-Z 2, 3 - /]pyrrole (287) in yields of 87% and 89%, respectively. Other isomers gave polymers or intractable materials 83JCS(P1)2551 . 

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Synthesis by Construction of the Second Heterocyclic Ring on to an Existing Heterocycle 539... 

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