RESUMO
Development of a general catalytic and highly efficient method utilizing readily available precursors for the regio- and stereoselective construction of bioactive natural-product-inspired spiro architectures remains a formidable challenge in chemical research. Transition metal-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides produces numerous N-heterocycles, but reaction control with the regioselectivity opposite to the conventional fashion has rarely been demonstrated. Herein, we report a unique ligand-controlled Cu(I)-catalyzed umpolung-type 1,3-dipolar cycloaddition of azomethine ylide to realize efficient kinetic resolution of racemic alkylidene norcamphors with the concomitant construction of previously inaccessible spiro N-heterocycles with high levels of regio- and stereoselectivity. The success of this methodology relies on the strategy of kinetic resolution, and the serendipitous discovery of a unique ligand-enabled regiospecific cycloaddition, which not only provides evidence for the existence of the minor zwitterionic resonance form in metallated azomethine ylide but also diversifies the existing chemistry of azomethine ylide-involved 1,3-dipolar cycloadditions with rare polarity inversion.
RESUMO
An unprecedented asymmetric Diels-Alder reaction of 3-hydroxy-2-pyrones with prochiral cyclopentene-1,3-diones via desymmetrization was efficiently realized with high stereoselective control with the aid of fine-tunable cinchona alkaloid derived bifunctional amine-thiourea catalysts bearing multiple hydrogen-bonding donors. This protocol provides an expedient access to the multifunctional-bridged tricyclic lactones featuring four contiguous stereogenic centers and one remote quaternary stereogenic center with a broad substrate scope. The cycloadduct can be readily elaborated into enantioenriched cyclopentane-1,3-diones via ring opening/aromatization.
