关键词:
aldehydes
alkaloids
conjugate addition
natural products
organocatalysis
摘要:
The aldehyde is arguably the most versatile carbonyl ***, it is more active than any other carbonyl functionality toward a plethora ofnucleophilic reactions. This unique combination of functional versatility and activity renderschiral aldehydes highly valuable intermediates in asymmetric synthesis. The emergence of numerouscatalytic enantioselective reactions that involve aldehydes as either nucleophiles or electrophilesfurther enhances the synthetic value of chiral aldehydes. Enantioselective transformations of thereadily available prochiral aldehydes are now emerging as a fundamentally important approach towardoptically active aldehydes. In particular, great strides have been made in the development ofenantioselective bond formations with the -carbon atom of prochiral aldehydes with chiral enaminecatalysis,[1], [2] enantioselective cycloadditions and Friedel-Crafts reactions with chiral immoniumcatalysis,[3] and conjugate additions of aryl boronic acids and silyl nitronates to ,-unsaturatedaldehydes by chiral transition-metal catalysis[4] and chiral phase-transfer catalysts,[5]respectively. Despite its synthetic importance, the highly enantioselective and general conjugateaddition of carbonyl donors to ,-unsaturated aldehydes remains elusive, even with considerableefforts.[6]-[8] Herein, we wish to report significant progress toward the development of such areaction with cinchona-alkaloid-derived organic catalysts.