Transition metal-free efficient synthesis of bis(indolyl)propynes (BIPs).

A transition metal-free approach has been devised for the synthesis of a variety of bis(indolyl)propyne (BIP) derivatives. The strategy involves an iodine-catalyzed cascade condensation of α,β-unsaturated acetylenic aldehydes with diversely substituted indoles. The strategy was applicable to gram scale synthesis and a library of 50 molecules, which were afforded in good to excellent yields (up to 96%), was developed. The salient features of the reaction involve the synthesis of indole based privileged scaffolds in a short reaction time under transition metal-free conditions, with a wide substrate scope and excellent yields under ambient conditions.