Ring contraction of larger rings is one of the important tools in the repertoire of the methods for the synthesis of pyrroles and has long been described in the literature. This methodology affords pyrrole derivatives with varied substituents, which are otherwise difficult to synthesize. Some of the examples of ring contraction leading to pyrrole have already been exemplified in various reviews, but there is no review focusing only the ring contraction strategy. Herein, we wish to focus on the synthesis of pyrroles by this strategy. The methods are mainly classified on the basis of the type of the starting heterocycle used. The synthesis of fused pyrrole systems such as indoles is also included as the special case. Thus, we herein discuss the methods comprising of the extrusion of an atom or a group of atoms from the larger ring or the opening of the larger rings and recyclization to afford the pyrroles.
Keywords: heterocycles, polypyrroles, pyridines, transformations
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