A remote β,γ-regioselective asymmetric inverse-electron-demand oxa-Diels-Alder reaction between allylic ketones and α-cyano-α,β-unsaturated ketones has been developed through induced extended dienamine catalysis of a cinchona-derived primary amine. A spectrum of densely substituted dihydropyran frameworks were efficiently produced with excellent enantioselectivity and fair to exclusive diastereoselectivity.
Regulating both the chemo- and diastereoselectivity, divergently, of a reaction is highly attractive but extremely challenging. Presented herein is a catalyst-controlled switch in the chemo- and diastereodivergent annulation reactions of Morita-Baylis-Hillman carbonates, derived from isatins and 2-alkylidene-1H-indene-1,3(2H)-diones, in exclusive α-regioselectivity. α-Isocupreine efficiently catalyzed [2+1] reactions to access cyclopropane derivatives, and the diastereodivergent [3+2] annulations were accomplished by employing either a chiral phosphine or a DMAP-type molecule. All reactions exhibited excellent chemoselectivities, and good to remarkable stereoselectivities were furnished, thus leading to a collection of compounds with skeletal and stereogenic diversity. Moreover, DFT computational calculations elucidated the catalyst-based switch in mechanism.
Efficient construction of a challenging aza-spirocycloheptane oxindole scaffold is reported through an unprecedented [4 + 3] cycloaddition reaction with bromo-substituted Morita-Baylis-Hillman adducts of isatins and N-(ortho-chloromethyl)aryl amides. Both reactive intermediates, the allylic phosphonium ylides and aza-o-quinone methides, were in situ generated, chemoselectively facilitated by a Lewis base and Brønsted base, respectively.
Regulating both the chemo‐ and diastereoselectivity, divergently, of a reaction is highly attractive but extremely challenging. Presented herein is a catalyst‐controlled switch in the chemo‐ and diastereodivergent annulation reactions of Morita–Baylis–Hillman carbonates, derived from isatins and 2‐alkylidene‐1H‐indene‐1,3(2H)‐diones, in exclusive α‐regioselectivity. α‐Isocupreine efficiently catalyzed [2+1] reactions to access cyclopropane derivatives, and the diastereodivergent [3+2] annulations were accomplished by employing either a chiral phosphine or a DMAP‐type molecule. All reactions exhibited excellent chemoselectivities, and good to remarkable stereoselectivities were furnished, thus leading to a collection of compounds with skeletal and stereogenic diversity. Moreover, DFT computational calculations elucidated the catalyst‐based switch in mechanism.
A [3+3] formal cycloaddition reaction between in situ formed azaoxyallyl cations and nitrones from isatins has been developed, furnishing a spectrum of spiro[1,2,4-oxadiazinan-5-one]oxindoles in good to excellent yields with excellent diastereoselectivity. This method provides direct and efficient access to potentially bioactive spirooxindoles incorporating a six-membered heterocyclic scaffold.
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