Morita–Baylis–Hillman reaction of indole-2-carboxaldehyde: new vistas for indole-annulated systems

DABCO-mediated Morita–Baylis–Hillman reactions of several 1-substituted-indole-2-carboxaldehydes are disclosed. It was discovered that carboethoxy or tert-butoxycarbonyl groups installed at N-1 undergo cleavage under the reaction conditions to afford 2-substituted indoles. Utility of the N-substituted adducts for preparing a variety of annulated indoles has been exemplified.