Formal C5-Alkylation of Indoles with Donor–Acceptor Cyclopropanes

Installing an indole C5 substituent bearing multiple reactive functional groups, either directly via S_EAr or any other methods or during indole construction using classic methods, remains challenging due to the inherently low reactivity at this position or limited functional-group tolerance. Reported herein is a mild, regioselective C5-alkylation of <i>N</i>-alkylindolines with donor-acceptor cyclopropanes (DACs), providing efficient access to C5-alkylated indolines. Selected products were then transformed into the corresponding indoles through a DDQ oxidation-hydrogenation sequence, constituting a formal C5-alkylation of indoles with DACs.