Selective lithiation of 2,3-dibromo-1-methylindole. A synthesis of 2,3-disubstituted indoles

Indole (1) can be converted to 2,3-dibromo-1-methylindole (3) in two operations (92% yield). Treatment of 3 with tert-butyllithium effects clean monolithiation to 3-bromo-2-lithio-1-methylindole (4), which can be trapped with various electrophiles to afford the 3-bromo-2-substituted indoles (5–8) in 85–99% yield. A second bromine–lithium exchange reaction and quenching with electrophiles yields the 2,3-disubstituted indoles (9–10) in 88–95% yield.