Aerobic Oxidations in Asymmetric Synthesis: Catalytic Strategies and Recent Developments

Pd-catalyzed Aerobic Cross-Dehydrogenative Coupling of Catechols with 2-Oxindoles and Benzofuranones: Reactivity Difference Between Monomer and Dimer

Persistent radicals, which are generated from 2-oxindole or benzofuranone dimers, are useful tools for designing the radical-based cross-coupling reaction to provide molecules containing a quaternary carbon. The persistent radical is accessible from both the dimer and monomer; however, the reactivity difference between these substrates for the oxidative cross-coupling reaction is not fully understood, most likely because of the mechanistic complexity. Here, we present details of an aerobic cross-dehydrogenative coupling (CDC) reaction using various monomers and catechols. UV-Vis analysis and mechanistic control experiments showed that the monomer is less reactive than the dimer under aerobic conditions. Our Pd(II)-BINAP-μ-hydroxo complex significantly improved the reactivity of the monomers for the aerobic CDC reaction with catechols, yielding results comparable to those of the corresponding dimer. The procedure, which enables the generation of the persistent radical in situ, is particularly useful when employing the monomer that is not readily converted to the corresponding dimer.

Highly Efficient Asymmetric Morita–Baylis–Hillman Reaction Promoted by Chiral Aziridine-Phosphines

Continuing our research on the use of organophosphorus derivatives of aziridines in asymmetric synthesis and expanding the scope of their applicability, chiral aziridine-phosphines obtained earlier in our laboratory were used as chiral catalysts in the asymmetric Morita–Baylis–Hillman reaction of methyl vinyl ketone and methyl acrylate with various aromatic aldehydes. The desired chiral products were formed in moderate to high chemical yields and with enantiomeric excess reaching value of 98% ee in some cases. The use of catalysts being pairs of enantiomers led to the desired products with opposite absolute configurations.

Visible-light-mediated oxidative C–S bond cleavage of benzyl thiols through in situ activation strategy

A novel method for the oxidative C–S bond cleavage of benzyl thiols was developed. In situ-activated silver species enabled the controlled bond cleavage of benzyl thiols to afford aldehydes and...