Triphenylphosphine/1,2-Diiodoethane-Promoted Formylation of Indoles with N,N-Dimethylformamide

Despite intensive studies in the synthesis of 3-formylindoles, it is still highly desirable to develop efficient methods for formylation of indoles due to the shortcomings of reported methods, such as inconvenient operations and/or harsh reaction conditions. Herein we describe a Ph3P/ICH2CH2I-promoted formylation of indoles with DMF under mild conditions. A Vilsmeier-type intermediate would be readily formed from DMF promoted by the Ph3P/ICH2CH2I system. A one-step formylation process could be extended to various electron-rich indoles, and a hydrolysis needs to be carried out as a second step in the case of electron-deficient indoles. Convenient operations may make this protocol attractive.