Yasutaka Kataoka

Stereoselective synthesis of (E)-alkenylsilanes from aldehydes with a reagent prepared by chromium(II) reduction of Me3SiCHBr2

Abstract Aldehydes are converted to the corresponding (E)-alkenylsilanes with one carbon homologation by means of a gemdichromium reagent prepared by CrCl 2 reduction of Me 3 SiCHBr 2 in THF. Transformation of aldehydes into alkenyl sulfides is also achieved with a combination of PhSCHCl 2 and CrCl 2 .

Regio- and stereoselective preparation of silyl enol ethers by alkylidenation of silyl esters

Abstract Treatment of trimethylsilyl esters with a reagent for alkylidenation of carbonyl groups derived from 1,1-dibromoalkane, zinc, TiCl4, and TMEDA in THF gives Z-trimethylsilyl enol ethers in a regio- and stereoselective manner.

Preparation of alkenyl sulfides and enamines by alkylidenation of carboxylic acid derivatives

Abstract Treatment of S-alkyl thioesters with a reagent prepared from RCHBr 2 , Zn, TiCl 4 , and TMEDA in THF at 25°C gives Z-alkenyl sulfides selectively in good to excellent yields. Using the alkylidenation method, ketene dithioacetals and enamines are produced from 1,3-dithian-2-one and amides, respectively.

Reduction of acetylenes to (Z)-olefins by means of low-valent niobium or tantalum.

Abstract Partial reduction of alkynes to (Z)-alkenes is achieved with the low-valent group 5 metal reagents prepared from MtlCl5 (Mtl = Nb or Ta) and zinc in a mixed solvent of DME (or THF) and benzene.

Preparation of 1-naphthols from acetylenes and o-phthalaldehyde using low-valent tantalum and niobium.

Abstract Tantalum (or niobium)-alkyne complexes are produced by treatment of acetylenes with the low-valent tantalum (niobium) derived by zinc reduction of TaCl 5 (NbCl 5 ). Substituted 1-naphthols are prepared regioselectively by reaction of o-phthalaldehyde with the tantalum (or niobium)-alkyne complexes in good to excellent yields.

Regioselective synthesis of highly substituted furans via tantalum-alkyne complexes.

Abstract A variety of 2,3,4-trisubstituted furans are prepared by treatment of tantalum-alkyne complexes with a aldehydes followed by addition of an isocyanide in DME-PhH-THF (1:1:1). The regioselectivity of the reaction depends on the bulkiness of substituents on a acetylenes and the bulkier substituents tend to possess 4-position of the produced furans. 4-Trialkylsilyl-substitued furans are produced exclusively when trialkylsilylacetylenes are employed.

Vanadium(II) complexes as efficient reagents for direct construction of asymmetric quaternary carbons from carbonyl compounds

Abstract Direct geminal diallylation of propiophenone with allyl bromide has been achieved in the presence of vanadium(II) species. By applying this method, direct construction of asymmetric quaternary carbons from propiophenone has been accomplished. Strong oxophilicity of the low-valent vanadium facilitated the deoxygenative reaction. The present reaction is characteristic of vanadium complexes.

Stereoselective addition of α-chloro allylic chromium reagents to aldehydes

Abstract Treatment of a solution of 1,1-dichloro-2-butene and benzaldehyde with CrCl2 in THF-DMF at 25°C for 1 h gave threo -(Z)-4-chloro-2-methyl-1-phenyl-3-buten-1-ol in 96% yield under high stereocontrol.

DIRECT CONSTRUCTION OF QUATERNARY CARBONS FROM CARBONYL COMPOUNDS UTILIZING LOW-VALENT VANADIUM COMPLEXES

Abstract Direct geminal diallylation of a carbonyl compound with allyl bromide has been achieved in the presence of a low-valent vanadium complex and zinc. The diallylation has been found to proceed stepwise and the two allyl groups were introduced successively. By applying this method, one-pot synthesis of asymmetric quaternary carbons has been accomplished. As the first alkylating reagent a combination of allyl bromide and zinc, a Grignard reagent, or an alkyllithium can be used. The second one should be the combination of a low-valent vanadium(II) complex and allyl bromide, benzyl bromide, or propargyl bromide. Strong oxophilicity of the low-valent vanadium facilitated the deoxygenative allylation.

Stereoselective preparation of primary (E)-allylic amines by the reaction of tantalum-alkyne complexes with metallo-imines

Abstract Treatment of tantalum-alkyne complexes with lithio-imines at 25∼50°C for several hours in the presence of Me 3 Al gives primary ( E )-allylic amines having adjacent tertiary carbons in good to excellent yields.