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α-Unsubstituted Pyrroles by NHC-Catalyzed Three-Component Coupling - Direct Synthesis of a Versatile Atorvastatin Derivative.


A practical one-pot cascade reaction protocol provides direct access to valuable 1,2,4-trisubstituted pyrroles. The process involves an N-heterocyclic carbene (NHC)-catalyzed Stetter-type hydroformylation using glycolaldehyde dimer as a novel C1 building-block, followed by a Paal-Knorr condensation with primary amines. The reaction makes use of simple and commercially available starting-materials and catalyst, an important feature regarding applicability and utility. Low catalyst loading under mild reaction conditions afforded a variety of 1,2,4-substituted pyrroles in a transition-metal free reaction with high step economy and good yields. This methodology is applied in the synthesis of a versatile Atorvastatin precursor which allows a variety of modifications at the pyrrole core structure.