Kazunori Hirabayashi

A novel C-C bond forming reaction of aryl- and alkenylsilanols. A halogen-free mizoroki-heck type reaction

Abstract When dimethyl(phenyl)silanol is subjected to on electron-deficient olefin in the presence of a stoichiometric amount of Pd(OAc)2, substitution of the CH bond of the olefin by a phenyl group on the silanol occurs in 52–86% yields. The reactions of several aryl- and alkenylsilanols with several olefins are also found to proceed in the system of 10 mol% of Pd(OAc)2, Cu(OAc)2 (3 mol), LiOAc (2 mol) to give the corresponding products in up to 69% yield.

Synthesis of cyclopropylsilanols by the Simmons-Smith reaction of alkenylsilanols and lithium alkenylsilanolates

Abstract Alkenylsilanols and the corresponding lithium silanolates prepared in situ by the reaction of cyclic siloxanes with alkenyllithiums are transformed to the corresponding cyclopropylsilanols under the Simmons-Smith reaction conditions. The obtained cyclopropylsilanols are further converted into the corresponding cyclopropanols by the Tamao oxidation.

Synthesis of a tetrabenzyl-substituted 10-membered cyclic diamide

Abstract A conformationally constrained 10-membered cyclic diamide was designed and synthesized. Conformational analysis suggested that the 9-membered ring formation was preferred to the direct formation of 10-membered ring. On the basis of the prediction, lactonization of 9-membered lactone, followed by intramolecular ester–amide transformation afforded the desired 10-membered cyclic diamide.

Copper(i) salt promoted homo-coupling reaction of organosilanes

Alkenylfluorosilanes, phenylfluorosilanes or alkynylsilanes smoothly dimerize in the presence of a copper(I) salt in a polar solvent such as N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) to give the 1,3-conjugated dienes, biphenyl or 1,3-conjugated diynes, respectively.

Palladium-catalyzed Mizoroki–Heck-type reactions of chalcogenonium trifluoromethanesulfonates

The reaction of dimethyl(4-methylphenyl)selenonium trifluoromethanesulfonate with butyl acrylate proceeded in the presence of palladium(II) catalyst and silver acetate to give a Mizoroki–Heck-type product. The corresponding sulfonium salt also reacted with butyl acrylate to afford the same product under similar conditions, although the yields were low. In the case of the corresponding telluronium salt, the reaction proceeded smoothly to give a good yield.

Isolation and Stereochemistry of Optically Active Selenoximines

Asymmetric selenoximines were synthesized and their optical isomers were isolated for the first time by optical resolution using chromatography with a chiral column. The absolute configuration was ...

Lewis acid–mediated reactions of propargyl chalcogenides with ethyl glyoxylate

GRAPHICAL ABSTRACT ABSTRACT The [3+2] cycloaddition reaction of mesityl propargyl sulfide with ethyl glyoxylate was found to occur by using tin(IV) chloride to give a 2,5-dihydrofuran derivative. On the other hand, when 3-silyl propargyl sulfides were used, allyl alcohols were obtained. In the case of propargyl sulfides possessing dimethyl groups at the α-position of the propargyl group, cycloaddition products were obtained even if a silyl group was present on the propargyl group. In addition, mesityl propargyl selenides also reacted with ethyl glyoxylate by using tin(IV) chloride to give the corresponding [3+2] cycloaddition products.

Optical resolution and racemization of areneseleninic acids

Various optically active areneseleninic acids (ArSeO2H; Ar = 4-Me-C6H4; 4-MeO-C6H4; 2-MeO-C6H4; 2-MeOCO-C6H4; 2,4,6-Me3-C6H2; 2,4,6-Et3-C6H2; 2,4,6-iPr3-C6H2; 2,4,6-tBu3-C6H2; 2,4-tBu2-6-MeO-C6H2) were obtained as solutions by optical resolution on a chiral column using medium-pressure liquid chromatography. Concentration of the eluate by evaporation under reduced pressure yielded completely racemized seleninic acids. Optically active seleninic acids with low-acidity were more stable against racemization than those with high-acidity. The bulky substituents at the ortho position on the benzene ring of the areneseleninic acids were also found to be effective for retarding the racemization. The mechanism for the racemization was clarified to proceed via seleninate anion with the extrusion of a proton under dilute conditions.

Synthesis and structures of partially unsaturated thiacrown ethers with hydroxyl groups

Partially unsaturated 14- and 28-membered thiacrown ethers possessing hydroxyl groups were synthesised. The crystal structures of some geometrical isomers of the macrocycles were determined by X-ray crystallographic analysis and six oxygen atoms of the 14-membered trans-thiacrown ether were found to gather through hydrogen bonds in the crystalline state. The redox behaviours of the 14-membered thiacrown ethers were examined and the Z,E-isomerisation reactions were found to occur upon heating.

Synthesis and Stereochemistry of Thiacrown Ethers with Unsaturated Bonds

Abstract Partially unsaturated 14- and 28-membered thiacrown ethers with Z-olefins were synthesized. The crystal structures of some of the macrocycles were determined by X-ray crystallographic analysis, and the 28-membered thiacrown ethers were found to have slender structures in the crystalline state. The 14-membered thiacrown ether without any substituent was found to be oxidized more easily than the corresponding thiacrown ether possessing hydroxyl groups. Heating of the 14-membered macrocycles was found to cause the Z,E-isomerization reactions to give the corresponding E,Z- and E,E-isomers.