Hiroaki Tsuji

Transition metal-catalyzed regioselective hydroboration of 1,3-dienes has been received continuous interests in the field of organic synthesis. Herein, we describe the nickel-catalyzed Markovnikov 1,2-hydroboration of in situ generated 1,3-dienes with bis(pinacolato)diboron using a secondary homoallyic carbonate as the 1,3-diene and hydride source. The catalytic hydroboration of in situ generated 1,3-dienes proceeded in the presence of Ni(cod)₂/P(p-MeOC₆H₄)₃ as the catalyst to give the corresponding secondary allylic boronates in 42–77% yields with high resioselectivity (12 examples).

The study for the development of the nickel-catalyzed highly enantioselective propargylic amination of propargylic carbonates with aniline derivatives is described. The reaction of internal alkyne-substituted propargylic carbonates with a series of aniline derivatives smoothly proceeded in DMSO using a combination of Ni(cod)₂ and (R)-SEGPHOS as the catalyst to give the corresponding chiral propargylic amines in 61–93% yields with 91–97% ee (24 examples).

The development of the transition‐metal‐catalyzed propargylic substitution of propargylic alcohol derivatives is one of the active research subjects in organic synthesis. In this minireview, we summarize the catalytic propargylic substitution of propargylic alcohol derivatives bearing an internal alkyne group using a transition metal as the catalyst. Although the asymmetric propargylic substitution of the substrate class still underdeveloped, some transition metal catalyses using nickel, palladium, and copper, and the cooperative catalysis enabled the challenging transformation. A various types of transition‐metal catalysts are known to promote the non‐asymmetric propargylic substitution of the internal alkyne‐substituted propargylic alcohol derivatives via a propargylic cation intermediate, realizing the carbon‐carbon and carbon‐heteroatom bond formation at the propargylic position.

We demonstrated a ruthenium-catalyzed regioselective allylic amination of tertiary allylic esters with various amines using [Cp*Ru(CH₃CN)₃][PF₆]/5,5′-dimethyl-2,2′-bipyridine (5,5’-diMe-2,2’-bpy) and related ruthenium catalytic systems, and successfully obtained a diverse range of α-tertiary amines as single regioisomers. The present ruthenium catalytic system was effective for reactions with various types of amines.

The nickel-catalyzed highly enantioselective Friedel–Crafts propargylation of 3-substituted indoles with propargylic carbonates bearing an internal alkyne group was developed. A wide array of the propargylic carbonates as well as 3-substituted indoles can be applicable to the asymmetric nickel catalysis, providing the corresponding chiral C-3 propargylated indolenine derivatives bearing two vicinal chiral centers in up to 89% yield with up to >99% ee and 94:6 dr (24 examples).

We have accomplished the ruthenium-catalyzed benzylic substitution of benzyl esters with a stabilized carbon nucleophile. A [Cp*RuCl₂]₂/picolinic acid catalyst system promoted the reaction of 2-naphthylmethyl-2,3,4,5,6-pentafluorobenzoates with a series of stabilized carbon nucleophiles such as malonates, β-ketoesters, and diketones to give the corresponding benzylic alkylation products in moderate to high yields. We proposed a plausible reaction mechanism that could involve a (π-benzyl)ruthenium intermediate.

The nickel-catalyzed hydroarylation of 1,3-dienes with arylboronic acids using a secondary homoallyl carbonate as a surrogate for the 1,3-diene and hydride source has been developed. The synthetic strategy allowed an efficient access to a wide array of hydroarylation products in high yields with high functional group compatibility without the use of an external hydride source. Mechanistic experiments indicated that the alkene-directed oxidative addition and subsequent β-hydride elimination would be a critical process in this transformation.

Nickel-catalyzed transformation of alkene-tethered oxime ethers to nitriles using a traceless directing group strategy has been developed. A series of alkene-tethered oxime ethers derived from benzaldehyde and cinnamyl aldehyde derivatives were converted into the corresponding benzonitriles and cinnamonitriles in 46–98% yields using the nickel catalyst system. Control experiments showed that the alkene group tethered to an oxygen atom on the oximes via one methylene unit plays a key role as a traceless directing group during the catalysis.