Copper-Catalyzed Selective Pyrrole Functionalization by Carbene Transfer Reaction

Article abstract of DOI:10.1002/adsc.201901629

1H-Pyrroles can be directly functionalized by means of the incorporation of carbene groups from diazo compounds, in a process catalyzed by Tp^xCu 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 D₂O serves to discard the direct insertion of the carbene group into the C_sp2?H bond, the alternative electrophilic attack to the pyrrole ring being feasible. (Figure presented.).