Synthesis of Pyrrolo[2,1,5-cd]indolizines through Dehydrogenative Heck Annelation of Indolizines with Diaryl Acetylenes Using Dioxygen as an Oxidant

A dehydrogenative Heck annelation reaction of indolizine with diaryl acetylene via dual C–H bond cleavage was developed. Oxygen gas was employed as a clean oxidant in this catalysis under base-free conditions. Diarylpyrrolo[2,1,5-cd]indolizines were synthesized with high atom economy. In addition, kinetic isotope experiments provided evidence for C–H bond metalation of the 5-position of the indolizine as the rate-limiting step.