The development of switchable chemo-, regio-, or diastereodivergent reactions, in which two or more structurally and stereogenically different types of chiral products could be produced efficiently from an identical set of starting materials under readily tunable catalytic conditions, is one of the ultimate goals in asymmetric catalysis. This tutorial review will focus on the application of a variety of chiral organic catalysts, including Lewis bases, and Brønsted bases and acids, in a diverse range of stereoselective reactions in a switchable manner. Meanwhile, a few examples of divergent reactions through synergistic activation of organocatalysis and metal catalysis will also be discussed.
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.
A direct catalytic asymmetric γ-regioselective vinylogous Michael addition of allyl alkyl ketones to maleimides has been developed through dienamine catalysis of a simple chiral 1,2-diphenylethanediamine, giving multifunctional products in excellent enantioselectivity and with high yields. The success of this catalytic strategy relies on the unique inducing effect of deconjugated β,γ-C═C bond, which facilitates the formation of the otherwise unfavored extended dienamine species.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.