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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