Synergistic Rhodium(II) Carboxylate and Brønsted Acid Catalyzed Multicomponent Reactions of Enalcarbenoids: Direct Synthesis of α‑Pyrrolylbenzylamines

The
design of a synergistic rhodium­(II) carboxylate and BINOL phosphoric
acid catalyzed efficient multicomponent reaction of enaldiazo compounds,
arylamines, and aryl aldehydes leading to the first transition-metal-catalyzed
direct synthesis of valuable α-pyrrolylbenzylamines is disclosed.
The reaction is proposed to involve a transient ammonium ylide of
a new class of electrophilic rhodium enalcarbenoid, its regioselective
Mannich reaction, and a cyclocondensation cascade. The methodology
was used in a highly diastereoselective synthesis of a binaphthyl
based chiral pyrrole.