Silylated thiiran-1-oxides: Structure,ring opening and conversion to a benzothiophene.

Silylated thiirans upon oxidation with peroxyacids do not give exclusively the corresponding S-oxides but, in addition some products derived from ring opening. The stereochemistry of the oxidation to thiiran-1-oxides is $\text{anti}$ to the silyl group as demonstrated by X-ray analysis.     

Synthesis of 1,2-benzisothiazolin-3-ones by ring transformation of 1,3-benzoxathiin-4-one 1-oxides

1,2-Benzisothiazolin-3-ones were synthesized from 1,3-benzoxathiin-4-one 1-oxides by means of a nonhazardous and inexpensive method. The 1,3-benzoxathiin-4-one 1-oxides were prepared by oxidation of 1,3-benzoxathiin-4-ones with hydrogen peroxide in the presence of a catalyst. Attack of amines on the carbonyl groups of the 1,3-benzoxathiin-4-one 1-oxides and subsequent elimination of carbonyl compounds likely produced sulfenic acids, which then underwent ring closure to afford the 1,2-benzisothiazolin-3-ones.     

1,2,5-Thiadiazole 2-oxides: selective synthesis,structural characterization,and electrochemical properties

A new general procedure for the selective synthesis of 1,2,5-thiadiazole 2-oxides (including fused derivatives) 8a,b,c,g,h from the reaction of vic-glyoximes with S₂Cl₂ and pyridine in acetonitrile was elaborated together with general procedure for the synthesis of 1,2,5-thiadiazoles 7a–i, 10, 12, and 14 from the same starting materials and reagents. Molecular structures of 3,4-dimethyl-1,2,5-thiadiazole 2-oxide 8a and [1,2,5]thiadiazolo[3,4-b]quinoxaline 10 were confirmed by single-crystal X-ray diffraction. Electrochemical properties of 1,2,5-thiadiazole 2-oxides 8 were studied by cyclic voltammetry and different behavior was observed for monocyclic and benzo-fused derivatives. With compounds 8g and 17, previously unknown deoxygenation of 2,1,3-benzothiadiazole 1-oxides was discovered by electrochemical reduction, and resulted 2,1,3-benzothiadiazoles 7g and 19 were detected in the forms of their radical anions by EPR spectroscopy combined with DFT calculations.     

Attempted reduction of 1,2,3-thiadiazole-4-carboxylates with samarium/iodine in methanol. Unexpected ring enlargement to 1,2,5-trithiepan-4,6-dicarboxylates

When stirred with powdered samarium and iodine in methanol at ice-cold temperature, ethyl 1,2,3-thiadiazole-4-carboxylate 5 underwent unusual reduction involving the dimeric ring enlargement with a sulfur addition, giving dimethyl 1,2,5-trithiepan-4,6-dicarboxylates 7a,b as a cis/trans-isomeric mixture in acceptable yield. The 1,2,3-thiadiazole ring of 5 proved to resist reduction by ordinary reducing agents, where the only choice in most cases was either recovery of the unchanged substrate or decomposition to an intractable mixture of unidentified products and tar.     

Convenient synthesis of 1-alkoxy-di- and tetrahydrophosphinine 1-oxides by ring enlargement

The double bond of the P-alkoxy 3,4-dimethyl-2,5-dihydro-1H-phosphole 1-oxides reacts easily with dichlorocarbene to give two diastereomers of an unstable adduct useful in the synthesis of ring expanded products, such as 1,2-dihydrophosphinine oxides or 1,2,3,6-tetrahydrophosphinine oxides. The former can be prepared by thermolysis of the adducts, while the latter are obtained by cyclopropane ring opening effected by silver nitrate in an alcoholic solvent. The preparation of the double-bond isomers of 1-alkoxy-tetrahydrophosphinine oxides containing only one methyl substituent in the ring is also described. The reaction of dihydro-1H-phosphole oxides with dichlorocarbene can be modified to give P-alkoxy 1,4-dihydrophosphinine oxides in an unexpected reaction.     

Convenient synthesis of 1-alkoxy-1,2-dihydrophosphinine 1-oxides by ring enlargement

The addition of dichlorocarbene to the double bond of 1-alkoxy-dihydrophosphole oxides and subsequent thermolysis of the adduct so obtained affords mixtures of the two double bond isomers of alkoxy-dihydrophosphinine oxides, if the latter step is carried out in the presence of triethylamine. Experimental data support the involvement of a cationic intermediate during the opening of the cyclopropane ring. A simplified procedure for the preparation of the starting dihydrophospholes is also presented.     

2H-1,2,4,6-thiatriazin-3(4H)-one 1-oxides and their regioselective N4-methylation and -amination

The syntheses of 2H-1,2,4,6-thiatriazin-3(4H)-one 1-oxides and 1,1-dioxides is described. The reaction of 1-carbamoyl-2-methylisothioureas 2 with thionyl chloride gave 2H-1,2,4,6-thiatriazin-3(4H)-one 1-oxides 3 in high yields. The treatment of 3 with either diazomethane or O-(2,4-dinitrophenyl)hydroxylamine furnished regioselectively N⁴-methylated and N⁴-aminated 2H-1,2,4,6-thiatriazin-3(4H)-one 1-oxides, respectively. Subsequent dimethylamination of 4 followed by oxidation with m-chloroperoxybenzoic acid led to 2H-1,2,4,6-thiatriazin-3(4H)-one 1,1-dioxides 6a-c .     

A new ring transformation of 3-halo-2-azidopyridine 1-oxides. A novel synthesis of 1,2-oxazin-6-ones

The course of the thermal ring-opening and recyclization of 2-azidopyridine 1-oxides is radically altered by the presence of a 3-halo substituent. Provided the 6-position is blocked, recyclization leads to a 6-cyano-6-halo-1,2-oxazine which hydrolyzes very readily to the 6H-1,2-oxazin-6-one. The structure of 4-bromo-3-methyl-6H-1,2-oxazin-6-one so obtained was confirmed by single crystal X-ray analysis. If the 6-position is not blocked, the product undergoes a further ring opening to give (Z)-β-cyanoacrylates.     

Heterocycles from substituted amides,V.. 1,2,3,5-Oxathiadiazolin-4-one 2-oxides from thionyl chloride and N-hydroxyureas

The reaction of certain N-hydroxy-N-methyl-N′-aryl ureas, 2 , with thionyl chloride are shown to give a new heterocycle, 1,2,3,5-oxathiadiazolin-4-one 2-oxides, 3 , in a synthesis that appears to have more severe structural requirements than the previously reported ring closures from α-hydroxyacylanilides and thionyl chloride. Isolable amounts of 3 are obtained only if the aryl group contains deactivating substituents, and the hydroxy group is attached to the N-alkyl nitrogen; otherwise, resin formation or ring chlorination are found to occur. The assigned structure as 3 was verified by a full three dimensional X-ray analysis of a representative example, 3a , 3-(4-bromophenyl)-5-methyl-1,2,3,5-oxathiadiazolin-4-one.     

5-氨基-6-硝基-[1,2,5]噁二唑并[3,4-b]吡啶-1-氧化物的新法合成

以2,6-二氯吡啶为起始原料,经肼基化、还原、硝化、Nietzki-Dietschy环合4步反应得到5-氨基-6-硝基-[1,2,5]噁二唑并[3,4-b]吡啶-1-氧化物.结合反应机理讨论了还原、硝化、Nietzki-Dietschy环合反应的影响因素,获得了合成-.氨基-6-硝基-[1,2,5]噁二唑并[3,4-b]吡啶-1-氧化物的最佳工艺条件,目标产物的总收率为59.2%.用1H NMR、MS和IR谱对5-氨基-6-硝基-[1,2,5]噁二唑并[3,4-b]吡啶-1-氧化物的结构进行了表征.     

A new ring transformation: Synthesis of 5,5-dimethyl-3-oxo-1-pyrroline 1-oxides from 6,6-dimethyl-4-oxo-5,6-dihydro-1,2,4h-oxazines

The nitrosation of some γ,δ-unsaturated β-diketo compounds affords the 3-substituted 4-oxo-5,6-dihydro-1,2,4H-oxazines. These compounds are converted to the isomeric 3-oxo-1-pyrroline 1-oxides by a facile thermal rearrangement.     

A new synthesis of pyrimido[5,4-e]-as-triazine 4-oxides and their ring transformation to pyrrolo[3,2-d]pyrimidines

A new synthesis of certain pyrimido[5,4-e]-as-triazine 4-oxides and their ring transformation to pyrrolo-[3,2-d]pyrimidines by the 1,3-dipolar cycloaddition reaction is described. Thus, reaction of 6-hydrazino-1,3-dimethyluracil ( 1 ) with triethyl orthoformate gave 6-ethoxymethylenehydrazino-1,3-dimethyluracil ( 2 ). Treatment of 2 with arylamines gave 6-arylaminomethylenehydrazino-1,3-dimethyluracils ( 3a-e ). Nitrosative cyclization of 3a-e with sodium nitrite afforded 3-arylaminofervenulin 4-oxides ( 6a-e ). Reaction of 6a-e with acetylenic esters yielded 7-alkoxycarbonyl-6-arylamino-1,3-dimethylpyrrolo[3,2-d]pyrimidine-2,4(1H,3H-diones ( 15a-e and 16 ).     

A new class of phosphanucleosides containing a 3-hydroxy-1-hydroxymethylphospholane 1-oxide ring

Novel phosphanucleosides containing a 3-hydroxy-1-hydroxymethylphospholane 1-oxide ring were synthesized as compounds with potential biological activity. A double Arbuzov reaction was employed to prepare a phospholene precursor, which was then converted into an epoxide and subsequently into racemic phosphanucleoside via nucleobase construction.     

Synthesis and investigation of antimicrobial activity of compounds derived from benzo[C][1,2,5]oxadiazole-1-oxides and phenolates

(Di)chloro(di)nitrobenzofuroxans form substitution products involving carbon atoms with phenolates in isopropyl alcohol medium. In the case of 4,6-dinitro-5,7-dichlorobenzofuroxan, besides replacement of one chlorine atom and the formation of C-bonded product, we observed the hydrolysis of the second chlorine and replacement of it by hydroxyl group. Products of reaction of 4,6-dichloro-5-nitrobenzofuroxan with phenolates display excellent antimicrobial activity and have dual action, both against bacteria and fungi.     

Synthesis of 3-substituted 4-imino-4,5-dihydro-1,2,3-triazole 1-oxides and 4-amino-1,2,3-triazole 1-oxides. Crystal and molecular structure of 4-imino-5,5-dimethyl-3-phenyl-4,5-dihydro-1,2,3-triazole 1-oxide

A new procedure for the synthesis of triazole N-oxides, based on base-induced intramolecular cyclization of 1-(-cyanoalkyl)-3-aryl(hetaryl)triazen-1-oxides, is proposed. An X-ray study of 4-imino-5,5-dimethyl-3-phenyl-4,5-dihydro-1,2,3-triazole 1-oxide was carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 746–751, April, 1993.     

Combined ab initio and density functional study of ring chain tautomerism in benzofurazan-1-oxide

The ring chain tautomerism of benzofurazan-1-oxide (benzofuroxan) has been reinvestigated using ab initio as well as nonlocal density functional theory. The failure in predicting energies and geometries of this reaction by wave functions at the Hartree-Fock or even at the MP2 level could be overcome by using the nonlocal three-parameter hybrid exchange correlation functional of Becke and Lee, Young, and Parr (B3-LYP). Two possible reaction paths via ortho-dinitrosobenzene have been studied, considering both ground and transition states. At the B3-LYP level of theory, both mechanisms show very similar activation energies which are in excellent agreement with experimental results. Solvent effects, simulated by a self-consistent reaction field (SCRF) model, cause alternations in the preferred mechanism as well as in the most stable intermediates. © 1996 by John Wiley & Sons, Inc.     

Synthesis and antiviral activity of 4H-[1,2,5]oxadiazolo-[3,4-d]pyrimidine-5,7-dione 1-oxide nucleosides

A series of 4H-[1,2,5]oxadiazolo[3,4-d]pyrimidine-5,7-dione 1-oxide nucleosides was designed,synthesized and evaluated against vesicular stomatitis virus(VSV)in Wish cell.The antiviral activities of all compounds were stronger than those of acyclovir,while their toxicities were similar to those of acyclovir.