Photocatalytic Alkylation of Pyrroles and Indoles with α‑Diazo Esters

This article describes the photoalkylation
of electron-rich aromatic
compounds with diazo esters. C-2-alkylated indoles and pyrroles are
obtained with good yields even though the photocatalyst loading is
as low as 0.075 mol %. For EWG-substituted substrates, the addition
of a catalytic amount of N,N-dimethyl-4-methoxyaniline
is required. Both EWG–EWG- and EWG–EDG-substituted diazo
esters are suitable as alkylating agents. The reaction selectivity
and mechanistic experiments suggest that carbenes/carbenoid intermediates
are not involved in the reaction pathway.