東郷 秀雄

Environmentally-friendly Wohl-Ziegler bromination of benzylic methyl groups was successfully carried out in ionic-liquid and solvent-free systems, to produce the corresponding benzylic bromides in good to moderate yields.

Radical cyclization and ionic cyclization onto the aromatic rings of 2-arylethanesulfonamides with polymer-supported hypervalent iodine reagents were examined, where the reactivities appear to be dependent on the substituent bonded to the nitrogen atom of 2-arylethanesulfonamides to obtain the corresponding 3,4-dihydro-2,1-benzothiazine 2,2-dioxides.

Primary and secondary alcohols were successfully oxidized to the corresponding aldehydes and ketones in good yields, respectively, with poly [4-(diacetoxyiodo) styrene] (PSDIB) in the presence of TEMPO (cat.) in acetone, as an environment-friendly method.

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.

Polymer-supported hypervalent iodine reagents, bearing (diacetoxy)iodo, (dihalo)iodo, (hydroxy)(tosyloxy)iodo, (hydroxy)(phosphoryloxy)iodo, aryliodonium, 1,2-benziodoxol-3-one, and hypervalent iodine groups as counter anions, can be used for various oxidative functional group conversions of substrates. These polymer species can be recovered quantitatively by simple filtration, and can be regenerated and reused. Thus, these polymer-supported hypervalent iodine reagents are very useful, effective, and environmentally benign reagents for organic synthesis.

Polymer-supported hypervalent iodine reagents, bearing (diacetoxy)iodo, (dihalo)iodo, (hydroxy)(tosyloxy)iodo, (hydroxy)(phosphoryloxy)iodo, aryliodonium, 1,2-benziodoxol-3-one, and hypervalent iodine groups as counter anions, can be used for various oxidative functional group conversions of substrates. These polymer species can be recovered quantitatively by simple filtration, and can be regenerated and reused. Thus, these polymer-supported hypervalent iodine reagents are very useful, effective, and environmentally benign reagents for organic synthesis.

Various N-alkylsulfonamides were easily dealkylated to give the corresponding free sulfonamides in moderate to good yields in the presence of (diacetoxyiodo)benzene and iodine under ultrasonic irradiation. Application of this methodology to various AT-protected alkylamines with sulfonyl, phosphonyl, and acyl groups was carried out, and the oxidative conversion occurred only in N-sulfonyl-protected phenylalkylamines to give the corresponding aldehydes together with free sulfonamides in moderate to good yields. (C) 2001 Elsevier Science Ltd. All rights reserved.

The synthetic utility of 1,1,2,2-tetraphenyldisilane as a new, environmentally benign radical mediator is discussed for the reduction, cyclization, reductive addition to olefins, and alkylation of heteroaromatic bases. (C) 2001 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.

Hypervalent iodine compounds, especially (diacetoxyiodo)arenes, have been used for the generation of (a) carbon-centered radicals through the decarboxylation of carboxylic acids or the beta -cleavage of alcohols, (b) oxygen-centered radicals from alcohols, hemi-acetals, or carboxylic acids, (c) nitrogen-centered radicals from amine derivatives. The radicals were employed for beta -fragmentation, oxidative addition and substitution, Barton-type reactions. Hofmann-Loffler-Freytag-type reactions, and reductive addition reactions, and successfully used for functional group transformation, formation of new skeletons and synthesis of natural products. 1 Introduction 2 Carbon-centered Radicals 3 Oxygen-centered Radicals 4 Nitrogen-centered Radicals 5 Miscellaneous.

Poly[4-hydroxy(tosyloxy)iodo]styrene (high M.W.) and poly(alpha -methyl [4-hydroxy(tosyloxy)iodo]styrene) (low M.W.) were prepared from polystyrene (average M.W.=45,000) and poly(alpha -methylstyrene) (average M.W. = 6,200), respectively, and their reactivities for the alpha -tosyloxylation of ketones and oxidative alpha -tosyloxylation of alcohols were compared with those of [hydroxy(to syloxy)iodo]benzene.

Iodophosphoryloxylation of carbon-carbon multibonds was attempted. Alkynes and cyclohexene were converted to the corresponding 1,2-iodophosphoryloxylated compounds in moderate to good yields with a trivalent iodine compound/iodine system, while glucal gave mainly the corresponding iodohydrin compound in this system. However, 2-deoxy-2-iodoglycosyl diphenylphosphinates were obtained from the corresponding glycals with a diphenylphosphinic acid/iodine/potassium carbonate system in good yields. Moreover, triethylborane smoothly reduced 2-deoxy-2-iodoglycosyl diphenylphosphinates to 2-deoxyglycosyl diphenylphosphinates in a 1,4-cyclohexadiene solvent.

Various N-alkylsulfonamides were easily dealkylated in moderate to good yields by the ultrasonic irradiation in the presence of (diacetoxyiodo)benzene and iodine.

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-h nu). On the other hand, irradiation of N-alkyl](o-methyl)arenesulfonamide derivatives bearing various substituents on the aromatic ring with a high-pressure mercury lamp (Hg-h nu), 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. (C) 1999 Elsevier Science Ltd. All rights reserved.

Poly[4-(diacetoxyiodo)styrene] is sufficiently reactive for the iodination of aromatics, the oxidative 1,2-aryl migration of alkyl aryl ketones, the alpha-hydroxylation of ketones, and the oxidation of hydroquinones and sulfides similarly to (diacetoxyiodo)benzene. Here, those reactions with poly[4- (diacetoxyiodo)styrene] are very useful because of the simple operation: thus, filtration gives the crude products and recovered poly(4-iodostyrene) and then poly[4-(diacetoxyiodo)styrene] can be regenerated by oxidation of the recovered poly(4-iodostyrene) which are reused for the same reactions.

Reactivity of tetraaryldisilanes as radical reducing agents of alkyl phenyl chalcogenides initiated by Et3B or AIBN was studied. Here, the reactivity of alkyl sulfide was poor; however, various alkyl phenyl selenides and tellurides were reduced to the corresponding hydrocarbons in good yields with 1,1,2,2-tetraphenyldisilane.

The reactivity of various iodanes, such as (diacetoxyiodo)arenes, the Dess-Martin reagent, and (arylsulfonyloxy)benziodoxolones, with (o-alkyl)- and (o-phenyl)arenecarboxylic acids in the presence of iodine (Suarez system)was studied to give the corresponding lactones via oxygen-centered radicals. (Diacetoxyiodo)arenes gave the lactones in good yields, while 1-(arylsulfonyloxy)benziodoxolones gave lactones together with the iodinated lactones. The Dess-Martin reagent also showed the same reactivity as (diacetoxyiodo)arenes to give the lactones. Among them, (diacetoxyiodo)toluene showed the best reactivity for the conversion of these carboxylic acids to the corresponding lactones.

1-Aryl-1,2,3,4-tetradeoxy-1,4-imino-D-pentitols 5 and 9f are easily synthesized from N-Boc-L-pyroglutamate I ria a successive procedure involving regioselective ring-opening, recyclization with dehydration, stereoselective reduction, and reduction of the ester group. Their structures are determined mainly by X-ray crystallography and NMR measurements. Their bioassay is also described.

The reactivity and synthetic use of 1-(arenesulfonyloxy)benziodoxolones were studied. In the presence of iodine, 1-(arenesulfonyloxy)benziodoxolones iodinated various aromatics to give iodoarenes in moderate to good yields. In particular, 1-(p-chlorobenzenesulfonyloxy)benziodoxolone showed the best reactivity. Using a halide salt such as lithium bromide or lithium chloride instead of iodine, the corresponding aryl bromides and chlorides were also obtained in good yields. In the absence of aromatics, 1-(arenesulfonyloxy)benziodoxolones gave rise to desulfonyloxyiodination reactions to give the corresponding aryl iodides via electrophilic ipso substitution on the aromatic rings. Furthermore, the 1-(p-toluenesulfonyloxy)benziodoxolone/iodine system iodotosyloxylated alkynes in good yields. These reactions proceeded via the formation of arenesulfonyl hypoiodites.

5-(Pyrimidinyl)magnesium and cerium chlorides were prepared via the halogen-metal exchange of 5-bromopyrimidine with ethylmagnesium chloride and a sequential treatment of butyllithium and cerium(III) chloride, respectively. In a similar way, 5-[2,4-di(tert-butoxy)pyrimidinyl]magnesium and cerium chlorides were prepared from the reaction of 5-bromo-2,4-di(tert-butoxy)pyrimidine with ethylmagnesium chloride and butylcerium chloride, respectively.

Reactivity of 1,1,2,2-tetraaryldsilanes 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. (C) 1999 Elsevier Science Ltd. All rights reserved.

1-beta-(4-Imidazoyl)- and 1-beta-(5-uracilyl)-1,4-dideoxy-1,4-imino-L-lyxitols were synthesized stereoselectively via a sequential procedure by the addition of the corresponding metal salts of heterocycles, Swern oxidation, reductive aminocyclization, and deprotection. Their structures were determined based on X-ray crystallography. From the NMR measurements of their N-acyl derivatives, two rotational isomers were observed. Their bioassay is also described.

Making use of the versatile character of the tellurium atom such as its radicophilicity, nucleophilicity and electrophilicity, D-ribofuranosyl, 2-deoxy-D-ribofuranosyl and D-glucosyl p-methoxyphenyl tellurides have been prepared. Under suitable conditions, the corresponding anomeric radical, anomeric cation and anomeric anion, respectively, are formed from the sugar tellurides. By the following coupling reactions of the anomeric radical and anomeric cation to electron-poor and electron-rich aromatics, respectively, the corresponding C-nucleoside analogues have been synthesized in moderate yields. The anomeric anion has also been trapped by an electrophile such as benzaldehyde.

'C-Aza-2-deoxy-L-lyxonucleosides' in which a sugar ring oxygen is replaced with a nitrogen atom are synthesized from 2-deoxy-3,5-O-(tetraisopropyldisiloxane-1, 3-diyl)-D-erythro-pentofuranose via a sequential procedure of the addition of lithium salts of aromatic heterocycles, Swern oxidation and reductive aminocyclization, Their structures are determined mainly by X-ray crystallography and NMR measurements. Their bioassay is also described.

The fundamentals of sugar anomer radicals and their reduction, addition, substitution, and rearrangement reactions are summarized. The preparation of C-glycosides and C-nucleosides via the formation of anomer radicals is reported.

Sulfonamides of primary amines bearing an aromatic ring at the gamma-position were treated with (diacyloxyiodo)arenes and:iodine under irradiation conditions with;a tungsten-lamp to give the corresponding 1,2,3,4-tetrahydroquinoline derivatives in moderate to good yields. Here, the reactivity depends on the Z-group (protecting group) of the starting amides. Under the same reaction conditions, some sulfonamides were treated with (diacetoxyiodo)benzene and iodine in the presence of aromatics to give the corresponding N-arylated amides. These reactions proceed through the intramolecular and intermolecular amidations onto aromatic rings via the sulfonamidyl radicals formed.

In recent years glycosyl fluorides have been utilized as versatile sugar donors in the field of organic synthesis including natural product synthesis as well as carbohydrate chemistry. We describe here an update on developments in the preparation and the utility of C-O, C-C, C-N, and CS bond formations, including total syntheses of natural products.

Poly[styrene(iodoso diacetate)] is sufficiently reactive to effect the iodination of aromatics and oxidative 1,2-aryl migration of alkyl aryl ketones as (diacetoxyiodo)benzene, and can be regenerated and reused for the same reactions.

Reactivity of 1,1,2,2-tetraphenyldisilane as a radical reagent in ethanol was studied in reduction of alkyl bromides, addition to olefin and alkylation onto heteroaromatic bases with alkyl bromides. The present organodisilane showed moderate to good reactivities for these three types of radical reactions. (C) 1998 Elsevier Science Ltd. All rights reserved.

Treatment of various aromatic compounds with 1-(p-toluenesulfonyloxy)-1,2-benziodoxol-3(1H)-one 1A and iodine gave the corresponding iodinated compounds in good yields. Similarly, chlorination and bromination proceeded effectively. As compared with other trivalent iodine compounds, the iodinane 1A showed the best reactivity as a halogenation reagent.