Takeshi Hondo

Lewis acid-promoted addition of methylenecyclopropanes to aldehydes and ketones

Abstract In the presence of TiCl 4 , methylenecyclopropane ( 1a ) easily reacted with aliphatic aldehydes to give the β-(chloromethyl)allylated products 2 in good yields along with a small amount of the methylenetetrahydrofurans 3 . The reaction with chiral α- and β-alkoxy aldehydes proceeded with high levels of chelation control.

ALLYLSTANNYLATION OF ALKYNES VIA A RADICAL PROCESS: STEREOSELECTIVE SYNTHESIS OF DI- AND TRI-SUBSTITUTED VINYLSTANNANES

Abstract In the presence of AIBN, allylstannanes bearing an electron-withdrawing group at the β-position easily reacted with terminal and electron-deficient internal alkynes to give β-allyl-substituted vinylstannanes in moderate to good yields. The allylstannylation proceeds with anti addition exclusively.

STEREOSELECTIVE SYNTHESIS OF 2,5-DISUBSTITUTED TETRAHYDROFURANS BY SILICON-DIRECTED CYCLIZATION OF VINYLSILANES BEARING A HYDROXY GROUP

Abstract In the presence of a catalytic amount of p -toluenesulfonic acid (TsOH) or TiCl 4 , (Z)-1-substituted-5-silyl-4-penten-1-ols can be easily transformed into 2,5-disubstituted tetrahydrofurans with high trans -selectivities.

Acid-catalyzed cyclization of vinylsilanes bearing a hydroxy group. Benzyldimethylsilyl group as an effective promoter and novel hydroxy surrogate

A benzyldimethylsilyl (BnDMS) group was found to effectively enhance the reactivity of vinylsilanes toward the acid-catalyzed intramolecular addition of a hydroxy group in comparison with a dimethylphenylsilyl group. The BnDMS group of the resultant cyclized products could be easily converted to a hydroxy group by the action of TBAF–H2O2–KHCO3.

Silicon-directed cyclization of vinylsilanes bearing hydroxy group catalyzed by an acid

Abstract Silicon-directed stereoselective syn addition of hydroxy group to olefinic double bond occurs intramolecularly in an acid-catalyzed cyclization of vinylsilanes bearing hydroxy group. Thus 5-dimethylphenylsilyl-4-penten-1-ol is smoothly cyclized to 2-(dimethylphenylsilyl)methyltetrahydrofuran upon the treatment of a catalytic amount ofp-toluenesulfonic acid (TsOH) or TiCl 4 .

STEREOSELECTIVE SYNTHESIS OF DI- AND TRISUBSTITUTED ALKENES VIA INTERMOLECULAR ADDITION OF VINYL RADICALS TO ALKENES

Abstract Vinyl radicals, generated from the reaction of vinyl iodides with tributylstannyl radical, react with electron-deficient alkenes to give di- or trisubstituted alkenes in moderate to good yields. The stereoselectivity is largely dependent on the substituent at 1- and 2-position of vinyl iodides.