Highly enantioselective synthesis of functionalized azepino[1,2-a]indoles via NHC-catalyzed [3+4] annulation.

The enantioselective [3+4] annulation of 3-formylindol-2-methyl-malonates with 2-bromoenals catalyzed by NHCs is described to afford functionalized azepino[1,2-a]indoles in high yields with excellent enantioselectivities. This method, in which the 3-formyl group in indoles acts as a necessary mediating group, provided cycloaddition products under mild conditions.