Enantioselective Synthesis of Pyrrolizidinone Scaffolds through Multiple-Relay Catalysis
Marcos Escolano1, Javier Torres Fernández1, Fernando Rabasa-Alcañiz1
1Department of Organic Chemistry, University of Valencia, Avda Vicente Andrés Estellés s/n, 46100 Burjassot-Valencia, Spain.
Abstract:
A triple-tandem protocol for the synthesis of the pyrrolizidinone skeleton has been devised. It involves a cross metathesis-intramolecular aza-Michael reaction-intramolecular Michael addition tandem sequence, starting from N-pentenyl-4-oxo-2-alkenamides and conjugated ketones. In the presence of two cooperative catalysts, namely the second-generation Hoveyda-Grubbs catalyst and (R)-TRIP-derived BINOL phosphoric acid, this multiple-relay catalytic process takes place in good yields and outstanding levels of diastero- and enantioselectivity with the simultaneous generation of three contiguous stereocenters.
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