Metal-Free Blue-Light-Mediated Cyclopropanation of Indoles by Aryl(diazo)acetates

Blue-light-mediated cyclopropanation of indoles with aryl(diazo)acetates has been developed. The salient features of this strategy are that it is metal-free, operationally simple and atom-efficient, and that it uses an environmentally friendly energy source. In this protocol, blue light was employed as the sole energy source for the transformation. A variety of cyclopropane-fused indoline compounds was obtained in moderate to excellent yields and high diastereoselectivities under mild conditions.