A new type of C(2)-symmetric chiral bisguanidine was designed as a highly efficient catalyst in the inverse-electron-demandhetero-Diels-Alderreaction of chalcones with azlactones for the first time. A wide variety of gamma,delta-unsaturated delta-lactone derivatives with alpha-quaternary-beta-tertiary stereocenters were obtained in high yields (up to 88%) with excellent enantioselectivities (up to
Highly enantioselective synthesis of γ-substituted butenolides via the vinylogous Mukaiyama–Michael reaction catalyzed by a chiral scandium(iii)–N,N′-dioxide complex
A highly efficient catalytic asymmetric vinylogous Mukaiyama–Michael reaction of the 2-silyloxyfuran with chalcone derivatives, catalyzed by a chiralN,N′-dioxide–scandium(III) complex, has been accomplished which tolerates a wide range of substrates. The reaction proceeds with complete regioselectivities, excellent diastereoselectivities (up to >99 : 1 dr) and good to excellent enantioselectivities
Reversal of Enantioselectivity by Tuning the Conformational Flexibility of Phase-Transfer Catalysts
作者:Ming-Qing Hua、Han-Feng Cui、Lian Wang、Jing Nie、Jun-An Ma
DOI:10.1002/anie.200906814
日期:2010.4.1
Towards perfect asymmetric catalysis: When binol‐derived N‐spiro quaternary ammonium salts were used as phase‐transfer catalysts in the conjugate addition of nitroalkanes to chalcones and its analogues, an intriguing reversal of enantioselectivity was observed. Novel chiral catalysts have been designed and synthesized (see structure).
The catalytic asymmetric aza-Michaelreaction of benzoyl hydrazine toward chalcones through the nonactivated amine moiety conjugated addition was facilitated by the developed N,N'-dioxide-Sc(OTf)(3) complex under mild conditions, affording the pharmacologically and synthetically useful products in moderate to high yields with up to 97% ee.
Stand and deliver: The first highly regio‐ and enantioselective bromoamination of chalcones has been developed which proceeds via an unusual bromonium‐based mechanism to deliver the title compounds. Excellent results were obtained using 0.05 mol % of the C2‐symmetric N,N′‐dioxide/scandium(III) complex under mild conditions (see scheme).