Gen Koga

A one-step and chemoselective conversion of silyl-protected alcohols into the corresponding acetates

Abstract A reagent system of acetyl bromide combined with a catalytic amount of tin(II) bromide cleaves readily trialkylsilyl ethers to give the corresponding acetates in high yields under very mild conditions.

Preparation of and dynamic gearing in cis-1,2-bis(9-triptycyl)ethylene

The two tortional degrees of freedom about the bond from the bridgehead to the olefinic carbons in cis-1,2-bis(9-triptycyl)ethylene couple slightly less strongly than those in the corresponding methane in spite of the apparently deeper meshing of the two triptycyl moiety, which manifests itself in the unusually large nuclear spin-spin coupling between the olefinic protons.

Correlation of the two torsional degrees of freedom about the bonds connecting the bridgehead carbons to the sulfur atom in bis (9-triptycyl) sulfide

Abstract Bis(9-triptycyl) sulfides were prepared by pyrolytic extrusion of sulfur dioxide from the corresponding thiosulfonates. A pair of torsional motions about the CS bonds in these sulfides are in strict gearing and require a barrier of 29.3 ± 0.3 kcal/mol for gear slippage.

The photolysis of diphenylcarbamoyl azide

Abstract In contrast to the thermal decomposition which produces 1-phenylindazolone in 90% yield, the photolysis of diphenylcarbamoyl azide in alcohols (and other solvents) gives 1-phenylbenzimidazolone, diphenylamine and the corresponding carbazates (except in t-amyl alcohol where no carbazate is formed), In no case could 1-phenylindazolone be isolated. The formation of 1-phenylbenzimidazolone is shown to proceed via the singlet diphenylcarbamoyl nitrene while the generation of diphenylamine is believed to occur by radical abstraction of the triplet nitrene. The carbazates arise by the Curtius rearrangement of the H bonded azide.

A novel and convenient synthesis of 2-aryl-4-methylenetetrahydrofurans from 2-(trimethylsiloxymethyl)allytrimethylsilane and acetals

Abstract The reaction of acetals with 2-(trimethylsiloxymethyl)allyltrimethylsilane under the influence of the combined use of a catalytic amount of tin(II) halide and acetyl halide affords the corresponding 2-aryl-4-methylenetetrahydrofurans in good yields.

o-trimethylsilylphenyllithium as a synthetic equivalent of o-halophenyllithium

Abstract The reaction of o-trimethylsilylphenyllithium with carbonyl compounds and subsequent halogenodesilylation with ICl afforded o-iodophenylcarbinols in good yields, showing the usefulness of o-trimethylsilylphenyllithium as a synthetic equivalent of o-iodophenyl anion. The reaction via a protected o-trimethylsilylphenylcarbinol is also shown.

Synthesis and crystal structure of 9,10-disilatriptycenes

9,10-Disilatriptycenes 1a–1chave been synthesized by a novel route via o-trimethylsilylphenyllithium, a novel synthetic equivalent of o-halogenophenyl anion; the structure of the 9-methyl-10-hydroxy derivative 1c was determined by X-ray crystallography.

The photolysis of 2-phenyltetrazole

The photolysis of 2-phenyltetrazole (1) in benzene yields phenylcyanamide (27%) and the phenylhydrazone of o-aminobenzoyl cyanide (53%) whose structure was determined by X-ray crystal structure analysis.