Copper‐Catalyzed Selective Pyrrole Functionalization by Carbene Transfer Reaction

1 H ‐Pyrroles can be directly functionalized by means of the incorporation of carbene groups from diazo compounds, in a process catalyzed by Tp x Cu complexes (Tp x =hydrotrispyrazolylborate ligand). The reactions take place with a complete selectivity toward the formal insertion of the carbene into the C α −H bond, leading to alkylated pyrroles, with no modification of the C β −H, N−H or C=C bonds of the pyrrole unit. Alkyl substituents at C‐ring as well as alkyl, aryl, allyl or alkyne substitution at N atom are tolerated, the strategy affording 20 new pyrrole derivatives. The observance of partial deuteration at the methylene group when the reaction is carried out with added D 2 O serves to discard the direct insertion of the carbene group into the C sp 2 −H bond, the alternative electrophilic attack to the pyrrole ring being feasible.