Hideo Togo

Direct and selective benzylic oxidation of alkylarenes via C-H abstraction using alkali metal bromides.

A direct benzylic oxidation of alkylarenes via C-H bond abstraction was developed using alkali metal bromides and oxidants under mild conditions. This reaction proceeded with excellent selectivity by thermal oxidation or photooxidation to provide a broad range of carbonyl compounds containing electron-deficient aryl carbonyl compounds in high yields.

Preparation of 3,5-disubstituted pyrazoles and isoxazoles from terminal alkynes, aldehydes, hydrazines, and hydroxylamine.

The reaction of terminal alkynes with n-BuLi, and then with aldehydes, followed by the treatment with molecular iodine, and subsequently hydrazines or hydroxylamine provided the corresponding 3,5-disubstituted pyrazoles or isoxazoles in good yields with high regioselectivity, through the formations of propargyl secondary alkoxides and α-alkynyl ketones. The present reactions are one-pot preparation of 3,5-disubstituted pyrazoles from terminal alkynes, aldehydes, molecular iodine, and hydrazines, and 3,5-disubstituted isoxazoles from terminal alkynes, aldehydes, molecular iodine, and hydroxylamine.

Facile radical decarboxylative alkylation of heteroaromatic bases using carboxylic acids and trivalent iodine compounds

Abstract Many kinds of heteroaromatic bases were easily alkylated by the reaction of carboxylic acids with [bis(trifluoroacetoxy)iodo]benzene or [bis(trifluoroacetoxy)iodo]pentafluorobenzene via radical decarboxylative pathways. This system was further applied to the reaction with tetrahydrofurylcarboxylic acid, 1-(2,3,5-tri-O-benyl)-D-ribofuranosylacetic acid, and 1-(2,3,5-tri-O-benzyl)-D-ribofuranosylcarboxylic acid for the model synthesis of C-nucleosides.

Oxidative intramolecular bromo-amination of N-alkenyl sulfonamides via umpolung of alkali metal bromides.

The oxidative intramolecular bromo-amination of various N-alkenyl sulfonamides and N-alkenoxyl sulfonamides via umpolung of alkali metal bromides occurred exo-selectively to generate cyclic bromoamides in high yields with good diastereoselectivities. This method provided the desired products without elaborating the stoichiometric amount of corresponding organic waste.

New synthetic method to 1,2-benzisothiazoline-3-one- 1,1-dioxides and 1,2-benzisothiazoline-3-one-1-oxides from N-alkyl(o-methyl) arenesulfonamides

Various N -alkylsaccharins were easily prepared in moderate to good yields by the reaction of N -alkyl( o -methyl)arenesulfonamides with (diacetoxyiodo)benzene in the presence of iodine under irradiation with a tungsten lamp (W-hν). On the other hand, irradiation of N -alkyl( o - methyl)arenesulfonamide derivatives bearing various subslituents on the aromatic ring with a high- pressure mercury lamp (Hg-hν), in the presence of (diacetoxyiodo)benzene and iodine gave the corresponding N -alkyl-1,2-benzisothiazoline-3-one-1-oxide derivatives in moderate yields, together with N -alkyl-1,2-benzisothiazoline-3-one-1,1-dioxide (saccharin) derivatives.

Remote functionalization (1): Synthesis of γ- and δ-lactones from aromatic carboxylic acids

Oxidative cyclization of o-alkyl- or o-arylaromatic carboxylic acids with [bis(trifluoroacetoxy)iodo]benzene and iodine via aromatic carbonyloxy radicals gave the corresponding lactones in good yields.

Novel preparation of 2,1-benzothiazine derivatives from sulfonamides with [hydroxy(tosyloxy)iodo]arenes

Cyclization of sulfonamides bearing an aromatic ring at the beta-position with various organohypervalent iodine compounds was carried out to form the corresponding 2,1-benzothiazine derivatives. Among them, the cyclization effectively proceeded with [hydroxy(tosyloxy)iodo]arenes through ionic pathways. The same treatment of a sulfonamide bearing a 4-methoxyphenyl group at the beta-position generated a spiro compound.

Tetraaryldisilanes as a novel strategic radical reagent

Abstract Reactivity of 1,1,2,2-tetraaryldisilanes as a radical reagent in ethanol was studied in reduction of alkyl bromides, addition to olefins and alkylation onto heteroaromatic bases with alkyl bromides. The present organodisilanes showed moderate to good reactivities for these three types of radical reactions. Among some disilanes prepared, 1,1,2,2-tetraphenyldisilane is the most useful in view of its reactivity and ease of preparation.

Selective Oxidation of Alcohols with Alkali Metal Bromides as Bromide Catalysts: Experimental Study of the Reaction Mechanism

A bromide-catalyzed oxidation of alcohols was developed which proceeded in the presence of an alkali metal bromide and an oxidant under mild conditions. The reaction involved an organic-molecule-free oxidation using KBr and Oxone and a Brønsted acid assisted oxidation using KBr and aqueous H2O2 solution to provide a broad range of carbonyl compounds in high yields. Moreover, the bromide-catalyzed oxidation of primary alcohols enabled the divergent synthesis of carboxylic acids and aldehydes under both reaction conditions in the presence of TEMPO. A possible catalytic mechanism was suggested on the basis of various mechanistic studies.

REMOTE FUNCTIONALIZATION : CYCLIC ALKOXYLATION ONTO AROMATIC RING VIA RADICAL PATHWAY

Abstract Oxidative cyclization of alcohols containing an aromatic ring with (diacetoxyiodo)benzene and iodine gave the corresponding cyclic ethers via alkoxy radicals in good yields. The present method is very useful for the direct preparation of flavonoid and vitamin E analogues from the alcohols.