Copper-Mediated Dimerization to Access 3a,3a′-Bis­pyrrolidino­indoline: Diastereoselective Synthesis of (+)-WIN 64821 and (−)-Ditrypto­phenaline

A copper-mediated cyclization and
dimerization of tryptamine or
tryptophan was developed to generate a C2-symmetry C3(sp3)–C3(sp3) bridge with two contiguous stereogenic quaternary carbons
in one step. Impressively, the ratio between exo and endo cyclization
products varies when different protecting groups of Nb are utilized.
This dimerization reaction could be conducted in gram scale. With
this dimerization method, both endocyclo­tryptophan (+)-WIN 64821
and exocyclo­tryptophan (−)-ditrypto­phenaline were
synthesized in 5 steps.