Practical Pd(TFA)2-Catalyzed Aerobic [4+1] Annulation for the Synthesis of Pyrroles via “One-Pot” Cascade Reactions

Abstract

Abstract:The Pd(TFA) 2 -catalyzed [4+1] annulation of chained or cyclic α-alkenyl-dicarbonyl compounds and unprotected primary amines for "one-pot" synthesis of pyrroles is reported here. Enamination and amino-alkene were involved in this practical and efficient tandem reaction. The annulation products were isolated in moderate to excellent yields with O 2 as the terminal oxidant under mild conditions. In addition, this method was applied to synthesize highly regioselective aminomethylated and di(1H-pyrrol-3-yl)methane products.

Synthesis of 2,3-Ring Fused Pyrroles via Cu-Catalyzed 5-exo-dig Annulation of Alkyne-Tethered Enaminones

“…The fused pyrrole products possess multiple synthetic handles for further transformations as shown in Scheme . Friedel–Crafts reactions of 2a with polyformaldehyde and imine under acidic conditions delivered the alkylation products 3 and 4 in 78% and 79% yields, respectively . Bromination reaction of 2a with NH 4 Br/oxone provided bromopyrrole 5 , a useful cross-coupling precursor, in 60% yield .…”

“…Friedel−Crafts reactions of 2a with polyformaldehyde and imine under acidic conditions delivered the alkylation products 3 and 4 in 78% and 79% yields, respectively. 17 Bromination reaction of 2a with NH 4 Br/oxone provided bromopyrrole 5, a useful crosscoupling precursor, in 60% yield. 18 Moreover, subjecting 2a to the Schmidt rearrangement conditions provided lactam 6 in 57% yield.…”