Synthesis of substituted indoles via a highly selective 7-lithiation of 4,7-dibromoindoles and the effect of indole-nitrogen on regioselectivity

We have developed an efficient synthetic pathway to rapidly access 4-bromoindoles, 4-substituted indoles, 4-bromo-7-substituted indoles, and 4,7-disubstituted indoles using a highly selective lithiation at the 7-position of 1-alkyl-4,7-dibromoindoles when treated with t-BuLi in ether. Based upon the selectivity obtained with 5,7-dibromoindoles in our previous study and with 4,7-dibromoindoles in the current study, we conclude that the alkylated indole nitrogen plays an important role in controlling selectivity.