The development of efficient and straightforward methods for obtaining all optically active isomers of structurally rigid spirocycles from readily available starting materials is of great value in drug discovery and chiral ligand development. However,t he stereodivergent synthesis of spirocycles bearing multiple stereocenters remains an unsolved challenge owing to steric hindrance and ring strain. Herein, we report an enantioand diastereodivergent synthesis of rigid spirocycles through dual-metal-catalyzed [3+ +2] annulation of oxy p-allyl metallic dipoles with less commonly employed nucleophilic dipoles (imino esters). Aseries of spiro compounds bearing apyrroline and an olefin were easily synthesized in an enantio-and diastereodivergent manner (up to 19:1 dr, > 99 %e e), which showed great promise as an ew type of N-olefin ligand. Preliminary mechanistic studies were also carried out to understand the process of this bimetallic catalysis.
A stereodivergent Pd/Cu catalyst system for asymmetric desymmetric alkylation of allylic geminal dicarboxylates has been developed, which was successfully applied to the asymmetric synthesis of βhydroxycarbonyl motifs bearing a versatile carbon-carbon double bond in an enantio-and diastereodivergent manner. A wide scope of substrates including challenging alkyl-substituted, 2-substituted, and 3,3'disubstituted allylic species are compatible with this catalytic system, delivering the substituted products in high to excellent yields and with excellent diastereoselectivities (up to >20:1 dr) and enantioselectivities (up to >99% ee). Furthermore, the mechanism of this dual Pd/Cu catalytic system including: a) the desymmetrization process of geminal dicarboxylates; b) the origin of regioselectivity (branched or linear); c) the enantio-and diastereoselectivity observed by changing the combinations of two chiral metal catalysts, have been carefully investigated by theoretical calculation.
The first asymmetric Ni/Cu cocatalyzed benzylation of aldimine esters is reported. A series of benzylsubstituted α-quaternary amino acids could be synthesized in high yield and with high levels of enantioselectivity (up to 90 % yield and 99 % ee). The experimental and theoretical calculation results suggested that the strong electrophilicity of the η 3 -benzylnickel intermediate is crucial for the high reactivity, enabling the reaction under base-free conditions. Furthermore, this method has been applied to the synthesis of the cell adhesion inhibitor BIRT-377 analogues, and the key intermediate of the NK1 receptor antagonist PD154075 and CCK-B receptor antagonist CI-988.
The stereodivergent synthesis of allene compounds bearing α,β-adjacent central chiralities has been realized via the Pd/Cu-catalyzed dynamic kinetic asymmetric alkylation of racemic allenylic esters. The matched reactivity of bimetallic catalytic system enables the challenging reaction of racemic aryl-substituted allenylic acetates with sterically crowded aldimine esters smoothly under mild reaction conditions. Various chiral non-natural amino acids bearing a terminal allenyl group are easily synthesized in high yields and with excellent diastereo-and enantioselectivities (up to > 20 : 1 dr, > 99 % ee). Importantly, all four stereoisomers of the product can be readily accessed by switching the configurations of the two chiral metal catalysts. Furthermore, the easy interconversion between the uncommon η 3 -butadienyl palladium intermediate featuring a weak C=C/Pd coordination bond and a stable Csp 2 À Pd bond is beneficial for the dynamic kinetic asymmetric transformation process (DyKAT).
A coumarinacyl
anilinium (CAA) salt, facilely synthesized
via a one-pot reaction, is shown to be a versatile visible and NIR
photoinitiator for cationic and step-growth polymerizations. CAA salt exhibits superior photoinitiation performance as
compared to commercial iodonium salt in cationic polymerization. Upon
visible-light irradiation, this salt undergoes hemolytic and heterolytic
cleavage and subsequent electron transfer and hydrogen abstraction
reactions, forming reactive species capable of initiating cationic
polymerization of epoxides and vinyl monomers. After a short irradiation
period, polymerization also proceeds in the dark due to the non-nucleophilic
nature of the counteranion. NIR-induced polymerizations were successfully
conducted based on upconversion photochemistry. CAA salt
can also initiate step-growth polymerization of N-ethyl carbazole (NEC) by oxidation of the monomer by the photochemically
formed anilium radical cations. Subsequent proton release and radical
coupling reactions essentially yield polycarbazole. CAA salt, featuring straightforward synthesis and long-wavelength sensitivity
as well as versatile photoinitiating performance, has great potential
in various applications.
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