A cooperative catalytic process through palladium and Brønsted acid activation is
developed for the conjugate addition of cyclic β-keto esters to azoalkenes directly
followed by hemiaminal formation upon cyclization. This transformation is enabled
by utilizing chiral Pd-aqua complexes as combined Brønsted acid–base catalysts. Thus,
bicyclic and highly functionalized dihydropyrroles with two contiguous quaternary
stereogenic centers are formed in excellent yields as single diastereomers and with
exceptional enantioselectivity.
Key words
asymmetric catalysis - azoalkenes - (3+2) cycloaddition - cooperative catalysis -
heterocycles - Pd-aqua complexes - Pd-enolates