Skeletal isomerism within 1,3-disilabicyclo[1.1.0]butane and 2,3-disilabuta-1,3-diene derivatives

A bis-adamantane-spiro-fused 1,3-bis(triisopropylsilyl)-1,3-disilabicyclo[1.1.0]butane equilibrates with the corresponding 2,3-bis(triisopropylsilyl)-1,3-disilabuta-1,3-diene with a ratio of 1:19. The 1,3-disilabuta-1,3-diene was fully characterized by a combination of multinuclear NMR and UV-VIS spectroscopies, elemental analysis, and single-crystal X-ray diffraction analysis.     

Substrate dependence in aqueous Diels-Alder reactions of cyclohexadiene derivatives with 1,4-benzoquinone

A reactivity difference based on the position of substituents on cyclohexa-1,3- diene was observed for the title reaction. The effect of water as solvent was more distinct for 1-methyl-4-isopropylcyclohexa-1,3-diene than for 2-methyl-5-isopropylcyclohexa- 1,3-diene or non-substituted cyclohexa-1,3-diene. The effect of NaCl (salting-out) and guanidium chloride (salting-in) was also large for 1-methyl-4-isopropylcyclohexa-1,3- diene.     

A convenient synthesis of new heterocycles from benzimidazoles and carbon suboxide

The reaction of carbon suboxide with 2-substituted benzimidazoles was investigated. By this reaction 1,3-diazino- (pyrimido-), 1,3-oxazino- and 1,3-thiazinobenzimidazole-1,3-diones are obtained.     

New chemical access for pyran core embedded derivatives from bisalkenylated 1,3-diketones and 1,3-diketoesters via tandem C-dealkenylation and cyclization

New chemical access has been developed for the synthesis of pyran core embedded derivatives from 1,3-diketones and 1,3-diketoesters, in which the active methylene group of 1,3-diketone or 1,3-diketoester was alkenylated with three equivalents of alkenyl bromides in presence NaH to give bisalkenyl 1,3-diketones or 1,3-diketoesters and the resultant bisalkenyl 1,3-diketones or 1,3-diketoesters were reacted with AlCl₃ at room temperature to furnish pyran core embedded derivatives in good to excellent yields.     

New Approach to the Synthesis of 1,3-Chloroisothiocyanatoalkanes. Synthesis of Tetrahydro-1,3-thiazine-2-thiones and 2-Alkylamino-5,6-dihydro-1,3-thiazines

A method was developed to prepare 1,3-chloroisothiocyanatoalkanes by reducing 1,3-isothiocyanato ketones using sodium borohydride at pH ~7 and subsequent treatment of the resultant 1,3-isothiocyanato alcohols with thionyl chloride. The reaction of 1,3-chloroisothiocyanatoalkanes with sodium hydrosulfide or amines gives substituted tetrahydro-1,3-thiazine-2-thiones or 2-amino-5,6-dihydro-1,3-thiazines.     

Tetracyanoethylene pi-complex chemistry. Indirect spectrophotometric determination of Diels-Alder-active 1,3-dienes

An indirect spectrophotometric method, based on the rapid Diels-Alder reaction between cisoid 1,3-dienes and tetracyanoethylene (TCNE) and the destruction of an aromatic-TCNE pi-complex, was developed to determine eleven 1,3-dienes in the 0.05-1.00 x 10(-3)M range. These dienes were: cyclopentadiene; 1,3-cyclohexadiene; trans-1,3-pentadiene; 2,4-dimethyl-1,3-pentadiene; trans-2-methyl-1,3-pentadiene; 2-methyl-1,3-butadiene; 9-methylanthracene; 9,10-dimethylanthracene; 1,6-diphenyl-1,3,5-hexatriene; 2,3-dimethyl-1,3-butadiene; and 1,4-diphenyl-1,3-butadiene. Three 1,3-dienes were determined in the 0.05-1 x 10(-4)M range: cyclopentadiene, trans-2-methyl-1,3-pentadiene, and anthracene. The limit of detection for cyclopentadiene in carbon tetrachloride solutions is 0.11 microg/ml. Fourteen 1,3-dienes were found to form stable pi-complexes and could not be determined by the proposed method. For these 1,3-dienes, the spectra of some of the complexes are reported; in addition, relative equilibrium constants for the pi-complexes of 2,5-dimethyl-2,4-hexadiene, cis-1,3-pentadiene, 4-methyl-1,3-pentadiene, and 1,3-cyclo-octadiene were estimated. An explanation of the transient colour in the 1,3-diene-TCNE Diels-Alder reaction is suggested.     

Photocyclization of 2-chloro-substituted 1,3-diarylpropan-1,3-diones to flavones

The photochemical behavior of 2-halo-substituted 1,3-diarylpropan-1,3-dione strongly depends on the nature of the halogen atom bonded and the presence of electron-donor groups on the phenyl ring. In the case of 2-chloro-1,3-diphenylpropan-1,3-dione and 1-(3,5-dimethoxyphenyl)-3-phenylpropan-1,3-dione, cyclization to flavones was the sole reaction pathway, whereas in the case of 2-chloro-1,3-di(4-methoxyphenyl)propan-1,3-dione, only products derived from alpha-cleavage were observed. 2-Fluoro derivatives of 1,3-diarylpropan-1,3-diones were photostable; on the other hand, 2-chloro-2-fluoro derivates resulted in 3-fluoroflavones.     

Self-condensation of β-(isoxazol-5-yl) enamines under treatment with acetyl chloride and acids. Synthesis of novel 1,3-diisoxazolyl-1,3-dieneamines and 1,3,5-triisoxazolyl benzenes

Two directions for self-condensation of β-(isoxazol-5-yl) enamines under treatment with either acetyl chloride or acids were found leading to new 1,3-diisoxazolyl-1,3-dieneamines and 1,3,5-triisoxazolyl benzenes. The effect of solvent, acid, temperature and the reaction time on the ratio of reaction products were investigated. Trans-E-cis configuration of prepared 1,3-diisoxazolyl-1,3-dieneamines was unambiguously confirmed by 2D NMR spectra and X-ray analysis. A new mechanism of 1,3-diisoxazolyl-1,3-dieneamines formation was proposed.     

Synthesis of 1,3-dithianes and 1,3-dithiolanes. Baker's yeast reduction and lipase-catalyzed resolution for synthesis of enantiopure derivatives.

Three 1,3-dithiolanes and four 1,3-dithianes have been synthesised from 1-(1,3-dithiolan-2-yl)-2-propanone and 1-(1,3-dithian-2-yl)-2-propanone, respectively. Asymmetric reductions of these ketones using baker's yeast gave the corresponding enantiopure (S)-alcohols. Baker's yeast also reduced the double bond in 3-(1,3-dithian-2-yl)-3-buten-2-one enantioselectively to give (S)-3-(1,3-dithian-2-yl)-2-butanone. 3-(1,3-Dithian-2-yl)-3-buten-2-one was also reduced chemo-selectively and the resulting 3-(1,3-dithian-2-yl)-3-buten-2-ol was resolved by transesterification in organic solvent using lipase B from Candida antarctica to yield the (S)-alcohol and the (R)-acetate with very high enantiomeric ratio, E. Racemic 1-(1,3-dithiolan-2-yl)-2-propanol and 1-(1,3-dithian-2-yl)-2-propanol were also resolved under similar conditions to give the (S)-alcohols and the corresponding (R)-acetates.     

Relative reactivities of cyclic ketene acetals via cationic 1,2-vinyl addition copolymerization1

The relationship between the relative reactivities of ten cyclic ketene acetals and their structures was determined via cationic copolymerizations of eight different monomer pairs. Thus, 2-methylene-1,3-dioxolane (1) was copolymerized with 2-methylene-4-methyl-1,3-dioxolane (2), 2-methylene-4,5-dimethyl-1,3-dioxolane (3), 2-methylene-4,4,5,5-tetramethyl-1,3-dioxolane (4), 2-methylene-4-phenyl-1,3-dioxolane (5), and 2-methylene-4-(t-butyl)-1,3-dioxolane (6). Also 2-methylene-1,3-dioxane (7) was copolymerized with 2-methylene-4-methyl-1,3-dioxane (8), 2-methylene-4,4,6-trimethyl-1,3-dioxane (9), and 2-methylene-4-isopropyl-5,5-dimethyl-1,3-dioxane (10). The relative reactivities of these monomers are: 3 > 5 > 4 > 2 > 1 > 6; and 10 > 9 > 8 > 7. In spite of steric demands, substituents at the 4- or 5-positions in 2-methylene-1,3-dioxolane and substituents at the 4- or 6-positions in 2-methylene-1,3-dioxane serve to increase the copolymerization reactivity. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2841–2852, 1999     

1,3-Dioxine diphenyl as a novel initiator for free-radical photopolymerization

1,3-Dioxane diphenyl, a novel photoinitiator for free-radical polymerization, was synthesized and characterized. UV-Vis absorption spectroscopy was used to investigate its photochemical behavior during the photophysical process. The photopolymerization kinetics of 1,3-dioxane diphenyl was studied by realtime infrared spectroscopy. There was an optimum curing rate with the increase of 1,3-dioxane diphenyl concentration. Both the polymerization rate and final conversion increased with the increase in light intensity. 1,3-Dioxane diphenyl was the most efficient photoinitiator for tripropylene glycol diacrylate and other acrylate monomers. 1,3-Dioxane diphenyl was a more effective photoinitiator than benzophenone/ethyl-4-dimethylaminobenzoate.     

Electrolytic partial fluorination of organic compounds.71. Highly diastereoselective anodic fluorination of sulfides having oxygen-containing heterocyclic groups

Diastereoselective anodic fluorination of sulfides having various oxygen-containing heterocyclic substituents such as 2-furanyl, 1,3-dioxolanyl, 2,2-dimethyl-1,3-dioxolanyl, 2-spirocyclohexyl-1,3-dioxolanyl, 2-spiroadamantyl-1,3-dixolanyl, and 1,3-dioxolanonyl groups at the beta-position was comparatively studied. Among the oxygen-containing heterocyclic substituents, the 2-spirocyclohexyl-1,3-dioxolanyl group gave the best diastereoselectivity (80% de). The diastereoselectivity was also affected by supporting fluoride salts and solvents. Chemical fluorination using selectfluor resulted in much lower diastereoselectivity and extremely poor yield. The fluorinated products were readily converted into the corresponding fluorinated diol in good yields by acidic hydrolysis.     

Cationic copolymerization of 2-vinyl-1,3-dioxane with styrene and 1,3-dioxolane

Copolymerization of 2-vinyl-1,3-dioxane with styrene and 1,3-dioxolane was carried out in methylene chloride at 0°C with triethyloxonium tetrafluoroborate as an initiator. Random copolymers were obtained from both of these monomer pairs, but attempted copolymerization of 2-vinyl-1,3-dioxane with 3,3-bis(chloromethyl)oxetane under similar conditions resulted in the homopolymer of the latter monomer. There were three structural units of 2-vinyl-1,3-dioxane in these copolymers as in its homopolymer: the “ester” unit, which was formed by vinyl addition with hydride shift followed by ring-opening rearrangement, the “vinyl” unit produced by ring-opening reaction, and the unit with a pendant 1,3-dioxane ring formed by simple vinyl addition. The fractions of the ester and vinyl units to the total 2-vinyl-1,3-dioxane units in the copolymer of 2-vinyl-1,3-dioxane with styrene decreased with decreasing 2-vinyl-1,3-dioxane content. On the contrary, the fraction of the vinyl unit in the copolymer of 2-vinyl-1,3-dioxane with 1,3-dioxolane increased slightly with decreasing 2-vinyl-1,3-dioxane content, while that of the ester unit decreased. The reactivities of the propagating species are discussed on the basis of these results.     

Polymeric mesoions, 3. Synthesis of polymeric mesoionic 1,3-diazinium-olates via polymer analogous modification of a polythiourea from m-phenylenediamine and p-phenylene diisothiocyanate

Mesoionic poly(1,1′-(1,3-phenylene)-3,3′-(1,4-phenylene)-bis(5-decyl-2-decylthio-4,6-dioxo-1,3-diazine)) ( 6 ) was prepared by cyclisation of the isothiourea component of poly(1,1′-(1,3-phenylene)-3,3′-(1,4-phenylene)-bis(2-decylisothiourea)) ( 4 ) with decylmalonic acid (5) by use of dicyclohexylcarbodiimide (DCC). Polymer 4 was obtained by polymer analogous alkylation of poly(1,1′-(1,3-phenylene)-3,3′-(1,4-phenylene)-bisthiourea) ( 3 ). For comparison of spectroscopic data, 5-butyl-2-propylthio-4,6-dioxo-1,3-diphenyl-1,3-diazine ( 9 ) was synthesized as low molecular weight model compound.     

A synthesis of lumazine derivatives

Treatment of 6-amino-1,3-dimethyl-5-nitrosouracil (Ia) with dimethyl acetylenedicarboxylate (DMAD) in dimethylformamide (DMF) afforded 6,7-bis(dimethoxycarbonyl)-1,3-dimethyllumazine (II). Similarly, the reaction of 6-amino-1,3-dimethyl-5-phenylazouracil with DMAD gave also II. Hydrolysis of II with hydrochloric acid gave 1,3-dimethyllumazine-6-carboxylic acid (III). III was chlorinated with thionyl chloride and then aminated with ethanolic ammonia to give rise to 6-carbamoyl-1,3-dimethyllumazine (V). V was alternatively synthesized by the treatment of Ia with propiolamide in DMF.     

Headspace gas chromatographic determination of 1,3-butadiene in simulated saliva

A headspace gas chromatographic (GC) method was developed to determine 1,3-butadiene (1,3-BD) in simulated saliva in contact with chewing gum. The calibration graph was linear, and the limit of detection was 0.004 mg/L, which is well below the migration limit for this substance. The headspace GC method provides rapid and reliable analysis for monitoring 1,3-BD migration from chewing gum into simulated saliva. In this paper, we report headspace methodology for sensitive determination of 1,3-BD in chewing gum and results of selected analyses, enabling preliminary assessment of possible exposure to 1,3-BD through migration.     

One-pot synthesis of new 2,4,5-trisubstituted 1,3-thiazoles and 1,3-selenazoles

In this work, we describe the synthesis of new 2,4,5-trisubstituted-1,3-thiazoles and 1,3-selenazole achieved by an easy one-pot four-step procedure. Expected compounds were obtained in good yield from dimethyl cyanodithioimidocarbonate, which was the common starting material for the preparation of all 1,3-thiazoles and 1,3-selenazoles. Chemical diversity was introduced on thiazole and selenazole rings by varying the amines and the activated halides used.     

The reaction of o-phthalaldchydic acid with 5-amino-1,3-dimethylpyrazole

o-Phthalaldchydic acid reacted with 5-amino-1,3-dimethylpyrazole to yield 5-amino-1,3-dimethyl-4-phthalidylpyrazole. The latter was transformed to a tricyclic system; 1,3-dimethylpyrazolo [3,4-b]benzazepin-9-one, which in turn was reduced with lithium aluminum hydride to 9,10-dihydro-1,3-dimethylpyrazolo[3,4-b]benzazepine.     

Synthesis of 1-Bromo-3-butyn-2-one and 1,3-Dibromo-3-buten-2-one

Synthetic procedures for the preparation of 1-bromo-3-butyn-2-one and 1,3-dibromo-3-buten-2-one are given. These compounds are prepared from 2-bromomethyl-2-vinyl-1,3-dioxolane, which can readily be prepared from 2-ethyl- 2-methyl-1,3-dioxolane. The synthetic routes are as follows: 2-bromomethyl-2-vinyl-1,3-dioxolane is converted to 2-(1,2-dibromoethyl)-2-bromomethyl-1,3-dioxolane. Double dehydrobromination with ^tBuOK affords 2-ethynyl-2-bromomethyl-1,3-dioxolane. Formolysis with formic acid gives 1-bromo-3-butyn-2-one. Deacetalized 2-bromoethyl-2-vinyl-1,3-dioxolane was treated with Br₂ and Li₂CO₃/12-crown-4 in tetrahydrofuran to give 1,3-dibrom-3-buten-2-one in moderate yield.     

Synthesis,Reactivity and Antimicrobial Activity of a Series of 2-Arylamino-1,3-selenazoles

A series of 2-arylamino-1,3-selenazoles was synthesized and their reactivity was studied. The 2-arylamino-1,3-selenazoles and their reaction products were characterized by various spectroscopic methods and X-ray diffraction. In addition, the antimicrobial activity of the 2-arylamino-1,3-selenazoles in a panel of seven bacteria and fungi was examined.