Transformations of heterocycles and carbocycles to pyrroles

The synthesis of pyrano[3,4-Z ]pyrroles was achieved utilizing a zinc-mediated ring contraction of pyridazines 07EJ03296 07SL403 . The pyridazines were formed by the cycloaddition of alkynes with tetrazines. 

A palladium-catalyzed ring expansion of aziridines provided a novel route to highly substituted pyrroles 07TL2267 . Treatment of methylene aziridines 33 with Pd(0) in the presence of symmetrical 1,3-diketones 34 led to the formation of 3-ketopyrroles 35. Pyrrole-substituted nucleoside analogues were prepared using a vanadium-mediated transformation of 2-azirines in the presence of symmetrical 1,3-diketones 07SL2723 . 

A novel ring opening reaction of cyclopropanes was discovered in the context of fused pyrrole synthesis 07OL5421 . For example, treatment of 1,1-dichlorocyclopropane 36 with LDA led to the production of fused pyrrole 37. The reaction likely proceeds through the formation of a carbene intermediate. 

An interesting non-oxidative transformation of pyrrolidine into pyrroles was reported 07JOC1518 . Heating pyrrolidine and aldehydes in toluene in a pressurized vessel led to the formation of 1,3-disubstituted pyrroles 38. 

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