Copper-Catalyzed Highly Enantioselective Cyclopentannulation of Indoles with Donor–Acceptor Cyclopropanes

A highly diastereo-
and enantioselective BOX/Cu­(II)-catalyzed C2,C3-cyclopentannulation
of indoles with donor–acceptor cyclopropanes has been developed
on the basis of asymmetric formal [3 + 2] cycloaddition of indoles.
This reaction provides rapid and facile access to a series of enantioenriched
cyclopenta-fused indoline products and can be further extended to
the construction of tetracyclic pyrroloindolines. The synthetic potential
of the reaction was demonstrated in a four-step synthesis of the core
structure of borreverine.