Copper-catalyzed regioselective trans-silaboration of internal arylalkynes with stereochemical switch to cis-addition mode

Regioselective Anti-Silyllithiation of Propargylic Alcohols

Among the known hydrosilylation or carbosilylation conditions of alkynes, anti-addition of the two units across the triple bond is considered rare compared to the syn counterpart. For anti-silylative vicinal difunctionalizations, transition-metal catalysts, such as ruthenium or palladium complexes, are generally required. Accordingly, silyl alkali metals have not been employed for those anti-addition transformations. Here we demonstrate that silyllithiums can add across the triple bond of a series of propargylic alkoxides regioselectively in an anti-fashion. Upon treatment with a variety of electrophiles, the trisubstituted alkenyl lithium intermediates were transformed into highly functionalized β-silyl allylic alcohols with high regiocontrol, eventually providing tri- or tetrasubstituted alkenylsilanes stereoselectively. A classic trick for anti-addition with propargylic alkoxides has transformed anti-silylative functionalizations into a robust and reliable strategy.

Copper-Catalyzed Regio- and Stereoselective Formal Hydro(borylmethylsilyl)ation of Internal Alkynes via Alkenyl-to-Alkyl 1,4-Copper Migration

Catalytic reactions involving 1,n-metal migration from carbon to carbon enable a nonclassical way of constructing organic molecular skeletons, rapidly providing complex molecules from relatively simple precursors. By utilization of this attractive feature, a new and efficient synthesis of alkenylsilylmethylboronates has been developed by formal hydro(borylmethylsilyl)ation of unsymmetric internal alkynes with silylboronates under copper catalysis. The reaction proceeds regioselectively and involves an unprecedented alkenyl-to-alkyl 1,4-copper migration. The reaction mechanism has been investigated by a series of kinetic, NMR, and deuterium-labeling experiments.

Copper(I)-Catalyzed Regio- and Stereoselective Silaboration of Terminal Allenes

Organic compounds bearing both silyl and boryl groups are important building blocks in organic synthesis because of the adequate reactivity of the silyl and boryl groups and high stereospecificity in their derivatization reactions. The difference in reactivity between the silyl and boryl groups enables stepwise derivatization of these groups to afford complex molecules. Here, we report the copper(I)-catalyzed silaboration of terminal allenes to produce multisubstituted allylic boronates embedded with an alkenyl silane structure. The reaction can proceed with a variety of allenes and silylboranes. Furthermore, the silyl and boryl groups were successfully converted into other functional groups, while retaining the stereochemistry of the alkene moiety.

A stable silylborane with diminished boron Lewis acidity

A new dimethyl(phenyl)silylborane having a naphthalene-1,8-diaminato (dan) substituent on the boron center, PhMe₂Si-B(dan), was synthesized. Owing to the diminished boron Lewis acidity, it is highly stable toward air. Synthetic application of the silylborane to catalytic silylboration and silylation of alkynes is also described.

Directed cis-hydrosilylation of borylalkynes to borylsilylalkenes

Directed by the choice of catalyst cis-hydrosilylation of borylalkynes leads to novel borylsilylalkenes which are crucial synthons for the introduction of the carbon–carbon double bonds in organic synthesis.