東郷 秀雄

Treatment of various 3-aryl-1-propanols with 1,3-diiodo-5,5- dimethylhydantoin (DIH) in ethyl acetate or 1,2-dichloroethane under irradiation with a tungsten lamp gave the corresponding chroman derivatives in good to moderate yields. The present reaction proceeds via the initial formation of an alkoxyl radical and the radical cyclization onto the aromatic ring, followed by the oxidation of the formed radical intermediate with DIH to provide the chroman derivative. The same treatment of o-biphenyldimethylcarbinol, o-phenylbenzoic acid, and o-alkylbenzoic acids with DIH provided the corresponding chroman derivatives and lactone derivatives in good yields, respectively. © Georg Thieme Verlag Stuttgart - New York.

Various alkyl aryl ketones, dialkyl ketones, and cycloheptanone were efficiently converted into the corresponding alpha-tosyloxy ketones in good yields by using Oxone (R) and p-toluenesulfonic acid monohydrate in the presence of p-iodotoluene in acetonitrile. 4-Methoxyacetophenone and 2-acetylthiophene bearing an electron-rich aromatic group could be also converted into the corresponding alpha-tosyloxyketones smoothly in good yields with the present method. Here, p-iodotoluene works as catalyst and p-[(hydroxy)(tosyloxy)]iodotoluene is formed in situ as a reactive species for the alpha-tosyloxylation of ketones. However, one equivalent of p-iodotoluene was required to obtain alpha-tosyloxyketones in good yields and was recovered in 80-20% yields, depending on the reaction conditions.

The reaction of alkyl aryl ketones with Oxone (R) and trifluoromethanesulfonic acid in the presence of iodoarene in acetonitrile, propionitrile, butyronitrile, and isobutyronitrile, provided directly the corresponding 2,5-disubstituted and 2,4,5-trisubstituted oxazoles, respectively, in moderate yields. Here, reactive aryliodonium I(III) species is formed in situ by the reaction of iodoarene with Oxone (R) and trifluoromethanesulfonic acid, and the formed aryliodonium I(III) species reacts with alkyl aryl ketone to generate beta-keto iodonium species. Then, beta-keto iodonium species reacts with nitrile to produce the corresponding oxazole. In principle, iodoarene works as a catalyst. However, I equiv of iodoarene is required because I equiv of reactive aryliodonium I(III) species must be formed before the reaction with alkyl aryl ketone. (C) 2009 Elsevier Ltd. All rights reserved.

Biphenyl- and terphenyl-based recyclable trivalent iodine reagents, such as 4-bromo-4'-(diacetoxyiodo)biphenyl, 4,4'-bis(diacetoxyiodo)biphenyl, 1,4-bis [4-(diacetoxyiodo)phenyl] benzene, 4-bromo-4'-[(hydroxy)(tosyloxy)iodo]biphenyl, 4,4-bis[(hydroxy)(tosyloxy)iodo]biphenyl, were simply prepared and their reactivities for the oxidative rearrangement of ketones to esters, TEMPO-mediated oxidation of alcohols to aldehydes or ketones, oxidative dealkylation of N-alkylsulfonamides to sulfonamides, and alpha-tosyloxylation of ketones were compared with p-(diacetoxyiodo)toluene and p- [(hydroxy) (tosyloxy)iodo] toluene to show the same reactivities and, moreover, the biphenyl- and terphenyl-based iodoarenes formed were recovered by simple filtration of the reaction mixture in every reaction. Thus, these biphenyl- and terphenyl-based trivalent iodine reagents can be used as the recyclable reagents. (c) 2006 Elsevier Ltd. All rights reserved.

The first C-4'-aminouridines can be synthesized in an alpha,beta-stereoselective manner starting from L-glutamic acid. For the synthesis of alpha-C-4'-aminouridine, a key compound 9 is cyclized with trifluoroacetic acid followed by reduction with NaBH3CN, while 9 is reduced with NaBH4 followed by mesylation to give beta-C-4'-aminouridine. Further, an acetonide-protection method is preferred for the synthesis of alpha-C-4'-aminouridine.

Thermolysis of perbenzylated D-glucopyranosediyl diazide 1 and D-galactopyranosediyl diazide 4 afforded, respectively, the corresponding 6-oxa-1,5-pentamethylenetetrazoles 2 and 5 via the sugar azido nitrenes, while, photolysis of diazides 1 and 4 gave, respectively, compounds 2 and 5 together with the corresponding by-products, 10-oxa-1,5-pentamethylenetetrazoles 3 and 6. Similarly, 5-(sugar chain)-substituted tetrazole 9 was obtained by the thermolysis of perbenzylated 1,1 -diazido acyclic sugar 8, while compound 9 and 1 -(sugar chain)-substituted tetrazole 10 were formed by the photolysis of compound 8. Interestingly, the thermolysis and photolysis of 1,1-diazido-2,3-di-O-benzyl-D,L-glyceraldehyde 8f gave both the corresponding 9f and 10f.

Heteroaromatic bases containing nitrogen atoms were easily alkylated with carboxylic acids in the presence of [bis(trifluoroacetoxy)iodo]benzene and [bis(trifluoroacetoxy)iodo]pentafluorobenzene via radical pathways. Similarly, the alkylation onto heteroaromatic bases was carried out with oxalic acid monoalkyl esters, which were prepared from alcohols and oxalyl dichloride, in the presence of the same trivalent iodine compounds. Moreover, this system was applied to the synthesis of C-nucleosides with the carboxylic acids bearing a sugar moiety.

Irradiation of O-acyl derivatives 1 of N-hydroxy- 2-thiopyridone with visible light in the presence of phenyl vinyl sulphone or vinyl triphenylphosphonium bromide leads to the corresponding adducts 8 and 9 which can undergo a wide variety of further transformations.

Recently, cosiderable attention has been given to many unnatural nucleosides since the appearance of some unnatural nucleosides as potential antiviral agents.^1 Thus, in connection with our study directed towards the synthesis of unnatural nucleosides, we present herein the first synthesis of sugar condensed isoxazolines and spiro sugar isoxazolidines. [1] Synthesis of Sugar Condensed Isoxazolines The oxidation of protected D-ribose oxime 1 with aqueous NaOCl solution gave the corresponding hydroximolactone 5, which was then allowed to react with dimethyl acetylenedicarboxylate (DMAD) in the presence of triethylamine, giving a 3:1 mixture of diastereoisomeric sugar condensed isoxazoline derivatives 7a and 8a in 85% yield. Their separation and deprotection were carried out by t.l.c. purification and HCl-MeOH treatment, respectively. The structures of 7a and 8a were determined mainly by NOESY measurement.^2 Further, D-deoxyribose, D-glucose, and D-galactose underwent the similar reaction to give the corresponding sugar condensed isoxazoline derivatives. [2] Synthesis of Spiro Sugar Isoxazolidines A mixture of D-ribose hydroximolactone 5, methyl acrylate, and dry toluene was heated in sealed tube to give the corresponding spiro sugar isoxazolidine derivative 22a in 85% yield. The tandem Michael addition-1,3-dipolar cycloaddition reaction gives 22a in a regio- and stereoselective manner because the ribose functions as a chiral template. Reduction of 22a with Raney nickel gave the corresponding pyrrolidone derivative 23, which was then changed into the corresponding pyrrolidine derivative 24 using LiAlH_4.^7 The structure of spiro sugar isoxazolidine 25 derived from methyl vinyl ketone was determined by single crystal X-ray diffraction. D-Glucose also underwent the similar reaction to give the corresponding spiro sugar isoxazolidine derivatives.