Iron‐ and Bismuth‐Catalyzed Asymmetric Mukaiyama Aldol Reactions in Aqueous Media

We have developed asymmetric Mukaiyama aldol reactions of silicon enolates with aldehydes catalyzed by chiral Fe^II and Bi^III complexes. Although previous reactions often required relatively harsh conditions, such as strictly anhydrous conditions, very low temperatures (?78 °C), etc., the reactions reported herein proceeded in the presence of water at 0 °C. To find appropriate chiral water‐compatible Lewis acids for the Mukaiyama aldol reaction, many Lewis acids were screened in combination with chiral bipyridine L1 , which had previously been found to be a suitable chiral ligand in aqueous media. Three types of chiral catalysts that consisted of a Fe^II or Bi^III metal salt, a chiral ligand ( L1 ), and an additive have been discovered and a wide variety of substrates (silicon enolates and aldehydes) reacted to afford the desired aldol products in high yields with high diastereo‐ and enantioselectivities through an appropriate selection of one of the three catalytic systems. Mechanistic studies elucidated the coordination environments around the Fe^II and Bi^III centers and the effect of additives on the chiral catalysis. Notably, both Brønsted acids and bases worked as efficient additives in the Fe^II‐catalyzed reactions. The assumed catalytic cycle and transition states indicated important roles of water in these efficient asymmetric Mukaiyama aldol reactions in aqueous media with the broadly applicable and versatile catalytic systems.     

Palladium‐Catalyzed Oxidative Carbocyclizations

Palladium‐catalyzed oxidative carbon–carbon bond‐forming annulations, that is, carbocyclization reactions, have recently emerged as efficient and atom‐economical routes to carbo‐ and heterocycles, whereby less functionalized substrates and fewer synthetic steps are needed to obtain a target molecule compared with traditional non‐oxidative carbon–carbon bond‐forming reactions. In this review, the synthetic efforts in palladium‐catalyzed oxidative carbocyclization reactions are summarized.     

Nickel‐Catalyzed Cross‐Coupling of Non‐activated and Functionalized Alkyl Halides with Alkyl Grignard Reagents

Reacting in the 'Ni'ck of time : The title reaction is realized by using an isolated Ni^II complex ( 1 ). The catalysis tolerates a wide range of important functional groups that are often incompatible with Grignard reagents in cross‐coupling reactions.

     

Palladium‐Catalyzed Carbon–Carbon Bond Formation and Cleavage of Organo(hydro)fullerenes

Palladium can tailor fullerenes : Palladium catalysts enable a number of C? H bond transformations of organo(hydro)fullerene. In addition to anticipated coupling reactions (C? H bond allylation and arylation), an unexpected new C? H bond dimerization reaction and C? C bond‐cleavage reaction were also uncovered.

     

Functional‐Group‐Tolerant Catalytic Migratory Oxidative Coupling of Nitrones

A copper‐catalyzed migratory oxidative‐coupling reaction between nitrones and various ethers/amines exhibited high functional‐group tolerance. Even in aqueous media, the reaction proceeded efficiently. For practical use of this catalysis, a unique sequential Huisgen cycloaddition was demonstrated. Mechanistic investigations revealed that the reaction proceeded through oxidative catalytic activation of ethers/amines to afford iminium/oxonium intermediates by concurrent dual one‐electron abstractions by copper(II) and oxyl radicals.     

Domino Cross Dehydrogenative Coupling of 2‐Aryl Acetals with Ketones Using DDQ as Oxidant and Reactant Precursor

A novel domino cross dehydrogenative coupling of 2‐aryl acetals with unmodified ketones has been developed, using DDQ as both the oxidant and reactant precursor.