The first electrochemical approach for nickel‐catalyzed cross‐electrophile coupling was developed. This method provides a novel route to 1,1‐diarylalkane derivatives from simple and readily available alkyl and aryl halides in good yields and excellent regioselectivity under mild conditions. The procedure shows good tolerance for a broad variety of functional groups and both primary and secondary alkyl halides can be used. Furthermore, the reaction was successfully scaled up to the multigram scale, thus indicating potential for industrial application. Mechanistic investigation suggested the formation of a nickel hydride in the electroreductive chain‐walking arylation, which led to the development of a new nickel‐catalyzed hydroarylation of styrenes to provide a series of 1,1‐diaryl alkanes in good yields under mild reaction conditions.
The synthesis and physicochemical properties of benzosiloxaboroles, the silicon analogues of an important class of heterocyclic compoundsbenzoxaborolesis presented. They were prepared by halogen−lithium exchange reactions of (2-bromophenyl)boronates with n-BuLi followed by the silylation or boronation of (2-lithiophenyl)dimethylsilanes. The cyclization of the resulting 2-(dimethylsilyl)phenylboronates apparently occurs through intramolecular dehydrogenative cyclization reaction in the presence of water. Unlike the case for benzosiloxaborole, the formation of its analogue containing a thiophene ring is thermodynamically unfavorable, which was confirmed by theoretical calculations. The presence of a B−O−Si linkage results in increased Lewis acidity with respect to the analogous benzoxaboroles. The acidity is strongly enhanced by fluorination or introduction of phenyl groups at the silicon atom. Selected compounds show good antifungal activity, and thus they are potential small-molecule therapeutic agents. They can also serve as effective receptors for biologically relevant diols under neutral pH conditions.
Herein we report a manganese catalyzed semihydrogenation of internal alkynes to (Z)-alkenes using ammonia borane as a hydrogen donor. The reaction is catalyzed by a pincer complex of the earth abundant manganese(II) salt in the absence of any additives, base or super hydride. The ammonia borane smoothly reduces the manganese precatalyst [Mn(II)-PNP][Cl] 2 to the catalytically active species [Mn(I)-PNP]-hydride in the triplet spin state. This manganese hydride is highly stabilized by complexation with the alkyne substrate. Computational DFT analysis studies of the reaction mechanism rationalize the origin of stereoselectivity towards formation of (Z)-alkenes.
The first manganese-catalyzed hydroboration of propargylic alcohols and amines as well as internal alkynes is reported. High regio-and stereoselectivity is achieved by applying 2 mol % of a manganese pre-catalyst based on the readily accessible bis(imino)pyridine ligand and MnCl2 as metal source. Propargylic alcohols and amines, as well as symmetric internal alkynes, were efficiently converted into the corresponding functionalized alkenes, which can serve as important and valuable intermediates for further synthetic applications such as cross-coupling reactions.
A highly selective hydrogenation of alkynes using an air stable and readily available manganese catalyst has been achieved. The reaction proceeds under mild reaction conditions and tolerates various functional groups resulting in (Z)-alkenes and allylic alcohols in high yields. Mechanistic experiments suggest that the reaction proceeds via a bifunctional activation involving metal-ligand cooperativity.
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