C3‐Formylation of Indoles in Continuous Flow

Abstract

We have developed a continuous flow C3‐formylation technique for indoles using hexamethylenetetramine (HMTA) and iodine. A mixed solvent system of DMF–H2O (1:1, vol/vol) completely dissolves reagents and prevents clogging of microchannels during fluid flow. The continuous flow technique provides maximized mixing and excellent heat transfer efficiency. Thus, flow chemistry accelerates the rate of C3‐formylation of indoles in the absence of a strong acid, base, or metal catalyst. We show that high yields of C3‐formylated indoles (up to 83%) can be obtained at 150°C when the residence time is as low as 8 min.