Kazuhiko Semba

Copper‐Catalyzed Hydrocarboxylation of Alkynes Using Carbon Dioxide and Hydrosilanes

to the corresponding methyl ester 2aMe.Byemploying [IPrCuCl] + tBuONa (Table 1, entry 1) or[IMesCuCl] + tBuONa (Table 1, entry 2) as a catalyst,2aMe was obtained in only trace amounts and 49% yield,respectively. In the latter case, a considerable amount (19%yield)ofcis-stilbene(3a)wasobservedasaby-product.When[IPrCuF]

Arylboration of Alkenes by Cooperative Palladium/Copper Catalysis

Arylboration of vinylarenes and methyl crotonate with aryl halides and bis(pinacolato)diboron by cooperative Pd/Cu catalysis has been developed, giving 2-boryl-1,1-diarylethanes and an α-aryl-β-boryl ester in a regioselective manner. The reaction is compatible with a variety of functionalities and amenable to be scaled-up to a gram scale with no detriment to the yield. A short synthesis of the biologically active compound CDP840 was performed using the present reaction as a key step.

Highly Selective Copper‐Catalyzed Hydroboration of Allenes and 1,3‐Dienes

The highly selective copper-catalyzed hydroboration of allenes has been developed. Allylboranes and alkenylboranes were selectively prepared by the judicious choice of catalytic species (copper hydride and boryl copper). Furthermore, two types of alkenylboranes could be selectively synthesized by the choice of an appropriate ligand. Mechanistic studies confirmed that the protonation of a (Z)-σ-allyl copper species, which was isolated and structurally characterized by single-crystal X-ray diffraction, was a key step in these reactions. Besides allenes, this method is also applicable to the selective hydroboration of 1,3-diene derivatives to afford allylboranes and homoallylboranes.

Intramolecular Aminocyanation of Alkenes by Cooperative Palladium/Boron Catalysis

A cooperative palladium/triorganoboron catalyst to accomplish the intramolecular aminocyanation of alkenes through the cleavage of N-CN bonds is reported. 4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) is found to be crucial as a ligand for palladium to effectively catalyze the transformation with high chemo- and regioselectivity. A range of substituted indolines and pyrrolidines with both tetra- or trisubstituted carbon and cyano functionalities are readily furnished by the newly developed cyanofunctionalization reaction. A preliminary example of enantioselective aminocyanation is also described.

Regioselective transformation of alkynes catalyzed by a copper hydride or boryl copper species

This review summarizes the transformation of alkynes using a copper hydride (Cu–H) or boryl copper (Cu–B) species as the active species. The semihydrogenation, hydrocarboxylation, and hydroboration of alkynes have been developed using Cu–H as the active species. The hydroboration, diboration, carboboration and boracarboxylation of alkynes involve the Cu–B species. These transformations afforded multi-substituted alkenes that are potentially good intermediates in organic synthesis. The key to the regioselective transformation is the addition of the Cu–H or Cu–B species to an alkyne, to afford the corresponding alkenylcopper intermediate regioselectively.

Copper‐Catalyzed Borylation of α‐Alkoxy Allenes with Bis(pinacolato)diboron: Efficient Synthesis of 2‐Boryl 1,3‐Butadienes

Something solid to build on: 2-Boryl 1,3-butadienes with various substitution patterns were formed in good to high yields in a copper-catalyzed borylation of α-alkoxy allenes with bis(pinacolato)diboron (see scheme; Bn=benzyl, pin=pinacolate, L is an N-heterocyclic carbene ligand). The products were found to be useful intermediates for the synthesis of cyclic vinyl boranes, α,β-unsaturated ketones, and functionalized multisubstituted dienes.

Anti-Markovnikov Hydroheteroarylation of Unactivated Alkenes with Indoles, Pyrroles, Benzofurans, and Furans Catalyzed by a Nickel–N-Heterocyclic Carbene System

We report the catalytic addition of C-H bonds at the C2 position of heteroarenes, including pyrroles, indoles, benzofurans, and furans, to unactivated terminal and internal alkenes. The reaction is catalyzed by a combination of Ni(COD)2 and a sterically hindered, electron-rich N-heterocyclic carbene ligand or its analogous Ni(NHC)(arene) complex. The reaction is highly selective for anti-Markovnikov addition to α-olefins, as well as for the formation of linear alkylheteroarenes from internal alkenes. The reaction occurs with substrates containing ketones, esters, amides, boronate esters, silyl ethers, sulfonamides, acetals, and free amines.

Reductive Cross‐Coupling of Conjugated Arylalkenes and Aryl Bromides with Hydrosilanes by Cooperative Palladium/Copper Catalysis

A method for the reductive cross-coupling of conjugated arylalkenes and aryl bromides with hydrosilanes by cooperative palladium/copper catalysis was developed, thus resulting in the highly regioselective formation of various 1,1-diarylalkanes, including a biologically active molecule. Under the applied reaction conditions, high levels of functional-group tolerance were observed, and the reductive cross-coupling of internal alkynes with aryl bromides afforded trisubstituted alkenes.

Arylboration of 1-Arylalkenes by Cooperative Nickel/Copper Catalysis

A method for the arylboration of 1-arylalkenes with bis(pinacolato)diboron and aryl chlorides or tosylates by cooperative Ni/Cu catalysis has been developed, which affords 2-boryl-1,1-diarylalkanes in high regio- and stereoselectivity. Under the applied conditions, this method is tolerant toward various functional groups, including silyl ether, alkoxycarbonyl, and aminocarbonyl moieties.

Site‐Selective Linear Alkylation of Anilides by Cooperative Nickel/Aluminum Catalysis

We report meta- and para-selective linear alkylation reactions of anilides with alkenes by nickel/N-heterocyclic carbene (NHC) and aluminum catalysis. With a less bulky NHC, the alkylation reaction of N-methyl-N-phenylcyclohexanecarboxamides proceeded mainly at the meta position. In contrast, a bulky NHC ligand led to the para-selective alkylation of N-sec-alkyl anilides.