Rose bengal as photocatalyst: visible light-mediated Friedel-Crafts alkylation of indoles with nitroalkenes in water.

A novel and facile visible-light-mediated alkylation of indoles and nitroalkenes has been developed. In this protocol, rose bengal acts as a photosensitizer, and environmentally benign water was used as the green and efficient reaction medium. Indoles reacted smoothly with nitroalkenes under the irradiation of visible-light and generated corresponding 3-(2-nitroalkyl)indoles in moderate to good yields (up to 87%).