G. L. Ciamician, M. Dennstedt, Ber. 14, 1153 (1881).
Expansion of the pyrrole ring by heating with chloroform or other halogeno compounds in alkaline solution. The intermediate dichlorocarbene, by addition to the pyrrole, forms an unstable dihalogenocyclopropane which rearranges to a 3-halogenopyridine:
A. H. Corwin, Heterocyclic Compounds 1, 309 (1950); H. S. Mosher, ibid. 475; P. S. Skell, R. S. Sandler, J. Am. Chem. Soc. 80, 2024 (1958); E. Vogel, Angew. Chem. 72, 8 (1960).