Toshimichi Ohmura

A new catalytic asymmetric process, the iridium-catalyzed enantioselective allylic amination of (E)-cinnamyl and terminal aliphatic allylic carbonates, was developed by exploring complexes of chiral phosphoramidites. The reaction provided branched secondary and tertiary allylic amines in high yields with excellent regio- and enantioselectivity (13 examples over 94% ee). Although the reactions in polar solvent such as DMF, EtOH, and MeOH were fast, they gave low enantiomeric excesses. In contrast

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTRhodium- or Iridium-Catalyzed trans-Hydroboration of Terminal Alkynes, Giving (Z)-1-Alkenylboron CompoundsToshimichi Ohmura, Yasunori Yamamoto, and Norio MiyauraView Author Information Division of Molecular Chemistry Graduate School of Engineering Hokkaido University, Sapporo 060-8628, Japan Cite this: J. Am. Chem. Soc. 2000, 122, 20, 4990–4991Publication Date (Web):May 4, 2000Publication History Received26 January 2000Published online4 May 2000P

Abstract New reactivities of silylboranes are described with their applications to organic synthesis. The silylboranes add to unsaturated organic compounds such as alkynes, alkenes, 1,3-dienes, and allenes in the presence of nickel, palladium, and platinum catalysts. Reactions with isocyanide proceed in the absence of catalysts, giving 1,1-addition products. The silaborations proceed in highly regio- and stereoselective manners, leading to the formation of organic compounds bearing silyl and bor

The first invertive B-alkyl Suzuki-Miyaura coupling has been achieved. The coupling of enantioenriched α-(acylamino)benzylboronic esters with aryl bromides and chlorides took place efficiently in toluene at 80 °C in the presence of Pd(dba)(2) (5 mol %), XPhos (10 mol %), K(2)CO(3) (3 equiv), and H(2)O (2 equiv). The reaction proceeded with inversion of configuration to give diarylmethanamine derivatives in high yields with high conservation of enantiomeric excesses.

An enantioselective silaboration of allenes was achieved using an achiral silylborane in the presence of a palladium catalyst bearing a chiral monodentate phosphine ligand. (R)-2-Bis(3,5-dimethylphenyl)phosphino-1,1'-binaphthyl gave the highest enantioselectivities in the addition of (diphenylmethylsilyl)pinacolborane to the internal C=C bond of terminal allenes at 0 degrees C, giving the corresponding beta-borylallylsilanes in high yields with high enantiomeric excesses. The enantioselectivity

An enantioselective silaborative C−C cleavage of meso-methylenecyclopropanes (meso-MCPs) was achieved by using a palladium catalyst bearing a chiral monodentate phosphine ligand. The (R)-2-bis(3,5-dimethylphenyl)phosphino-1,1‘-binaphthyl gave the highest enantioselectivity in the reactions with (methyldiphenylsilyl)pinacolborane at 50 °C, affording derivatives of 2-boryl-4-silyl-1-butene in high yields with high enantiomeric excesses. The reactions of bicyclic MCPs that have fused five- to eight

The regioselectivity in the addition of silylboronic esters to terminal alkynes can be switched by the choice of phosphorus ligands on the palladium catalysts. The silaboration proceeds with normal regioselectivity in the presence of (eta(3)-C(3)H(5))Pd(PPh(3))Cl (1.0 mol %) to give 1-boryl-2-silyl-1-alkenes in high yields. In sharp contrast, selective formation of the inverse regioisomers, 2-boryl-1-silyl-1-alkenes, takes place when the reaction is carried out with a palladium catalyst bearing

A methyl group of methylchlorosilanes undergoes C-H borylation in an iridium-catalyzed reaction with bis(pinacolato)diboron in cyclohexane at 80 °C, giving (borylmethyl)chlorosilanes selectively.

The iridium complex generated in situ from [Ir(cod)Cl]2 and a phosphine ligand catalyzed the dimerization of terminal alkynes to give (E)-enyne, (Z)-enyne, or 1,2,3-butatriene derivatives in the presence of triethylamine. The triarylphosphine complex selectively yielded linear (E)-enynes for silylethynes, while the tripropylphosphine complex provided linear (Z)-enynes for silylalkynes or 1,2,3-butatrienes for tert-alkylethynes.

Silylpinacolboranes bearing dialkylamino groups on the silicon atom served as synthetic equivalents of silylene in palladium-catalyzed reactions with terminal alkynes, leading to the formation of 2,4-disubstituted siloles in high yield. It was found that the amino group on the silicon atom was critically important for the reaction; no silole products were found in reactions using silylpinacolboranes carrying aryl, chloro, or alkoxy groups on the silicon atoms. Site-selective bromination of 1,1-d

Silylboronic esters bearing a dialkylamino group on the silicon atoms reacted with 1,3-dienes in the presence of a palladium catalyst to give silacyclopent-3-enes (i.e., 2,5-dihydrosiloles) in high yields via efficient silylene transfer from the silylboronic ester to the 1,3-dienes. The [4 + 1] cycloaddition was applicable to the parent 1,3-butadiene and various mono-, di-, and trisubstituted 1,3-dienes having silyloxy, cyano, and ester groups. Stereospecific ring formation took place in the rea

A 4,4'-bipyridine-based catalyst system for diboration of pyrazine derivatives was established. The catalyst cycle consists of the following two steps: (1) reductive addition of the boron-boron bond of bis(pinacolato)diboron to 4,4'-bipyridine to form N,N'-diboryl-4,4'-bipyridinylidene and (2) oxidative boryl transfer from the intermediate to pyrazine to give N,N'-diboryl-1,4-dihydropyrazine with regeneration of 4,4'-bipyridine.

Palladium-catalysed cis- and trans-silaboration of terminal alkynes has been developed via the addition of (chlorodimethylsilyl)pinacolborane, followed by a one-pot conversion of the chloro group on the silicon atom to an isopropoxy group.

The stereoselective isomerization of allyl silyl ethers to (E)- or (Z)-silyl enol ethers was carried out in the presence of a cationic iridium(I) catalyst. The complex, prepared in situ by treating [Ir(cod)2]PF6/2PPr3 with hydrogen, was found to be an excellent catalyst for the isomerization of primary and secondary allyl ethers in high yields. The primary allyl silyl ethers produced (E)-enol ethers and the secondary allyl ethers afforded (Z)-enol ethers with high stereoselectivity, often exceed

New silylpinacolboranes bearing chloro, fluoro, alkoxy, and dialkylamino groups on silicon were synthesized in high yields via derivatization of [(diethylamino)diphenylsilyl]pinacolborane, which was prepared by reaction of [(diethylamino)diphenylsilyl]lithium with (isopropoxy)pinacolborane, and (chlorodimethylsilyl)pinacolborane, prepared by reaction of (dimethylphenylsilyl)pinacolborane with hydrogen chloride in the presence of a catalytic amount of aluminum chloride.