Copper-catalyzed [4+1]-annulation of 2-alkenylindoles with diazoacetates: a facile access to dihydrocyclopenta[b]indoles.

A copper-catalyzed [ 4+ 1]-annulation of 2-vinylindoles with diazoacetates has been developed that provides a straightforward access to the dihydrocyclopenta[ b] indoles bearing two contiguous all-carbon quaternary centers in good yields. Mechanistic studies indicate that the reaction goes through a concerted and asynchronous annulation process via the key zwitterionic intermediate.