Synthesis of fused indoline heterocycles via dearomatization of indoles with α-bromohydrazones: a systematic study on the substrates.

An efficient metal-free dearomatization of indoles with α-bromohydrazones is reported. Various fused indoline heterocycles, which are potentially biologically active, were achieved in good yields (up to 94%) under mild conditions. A systematic study on electronic- and steric effects of substrate and reagents revealed that they have great influence upon the reaction. Based on this, the scope of indoles and α-bromohydrazones was widely exploited.