Search

Unlike its trans counterpart, the cis-configured scaffold derived from the Castagnoli–Cushman reaction (CCR) is scarce and has not been explored in bioactive compound design. We found that conducting this reaction in DMF (in contrast to conventional toluene or xylene) led to a significantly higher proportion of cis-configured lactams in the diastereomeric product mixture. This allowed us, for the first time, to obtain and thoroughly characterize both stereoisomers of a significant number of lead-like CCR lactams. Simple rules for 1H NMR-based stereochemical assignment have been devised and correlated with the single-crystal X-ray structures obtained for pure cis- and trans-configured lactams.

One-pot, three-component preparation of the pyrrolizidine and pyrrolizinone derivatives in moderate to good yield is reported. The synthesis is facilitated by microwave irradiation of proline, aromatic aldehyde, and 1,3-diketone such as 2-arylmethylene-indene-1,3-dione and 4-hydroxycoumarin in 1,4-dioxane or xylene. This method provides a quick access to the multi-functionalized pyrrolizidines and pyrrolizinones.

All reactions are performed in toluene as well as xylene with the latter delivering lower product yields.

Direct carboxylation of simple arenes under atmospheric pressure of CO2 is achieved through a rhodium-catalyzed C–H bond activation without the assistance of a directing group. Various arenes such as benzene, toluene, xylene, electron-rich or electron-deficient benzene derivatives, and heteroaromatics are directly carboxylated with high TONs.

A new route for the regioselective synthesis of 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole derivatives was developed based on cyclization of 3-chlorophenylimine-N-alkyl-4-piperidones by “the complex bases” of NaNH2 or KNH2. The procedure was performed under variable reaction conditions in inert proton-free solvents, such as THF, dioxane, 1,2-dimethoxyethane, toluene, and xylene, at temperatures varying from 20°C to boiling point of the solvent used. Toxic arylhydrazine intermediates occurring in the classical Fischer indole synthesis are avoided.

A readily accessible catalytic system, PdCl 2 (Ph 3 P) 2 /Ph 3 P, was developed for the selective arylation of primary anilines with aryl bromides. The strong influence of solvents and bases on the catalytic activity was observed. In refluxing o -xylene, triphenylphosphine shows high efficiency for Pd-catalyzed intermolecular amination reactions. By changing the bases, mono- and diarylation of primary amines could be selectively achieved in high yields. Moreover, the catalytic system showed good toleration for the steric hindrance of anilines. A series of N , N , N ′, N ′-tetraaryl-1,1′-biphenyl-4,4′-diamines, important intermediates of OLED hole transport materials, were synthesized facilely via coupling reactions between 4,4′-diaminobiphenyls and aryl bromides.

Thermal-induced dimerization cyclization of ethyl N-(styrylcarbamoyl)acetate derivatives has been investigated, leading to 4-hydroxy-2(1H)-pyridone-3-carboxamide derivatives with good yields in diphenyl ether on 200–210 °C. Ethyl N-(styrylcarbamoyl)acetate derivatives readily provided the intermolecular cyclization products 4-hydroxy-2(1H)-pyridone-3-carboxylates on reflux in xylene. In addition, several related 3-acetyl-4-hydroxy-5-phenylpyridin-2(1H)-ones have been prepared. It provided an efficient preparation of 4-hydroxy-2(1H)-pyridone-3-carboxamide derivatives.

3-Hydroxymethylchromones have been found to undergo a novel transformation in the presence of Cs2CO3 in toluene or xylene as solvent to afford “trimeric” chromones, 3,3-bis-(4-chromone-3-ylmethyl)-chroman-4-ones. The structure of the trimer has also been confirmed by single-crystal x-ray diffraction study. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.

A novel one-pot synthesis of 1,3,4-trisubstituted pyrazoles has been accomplished by 1,3-dipolar cycloaddition of α,β-unsaturated ketones and 3-arylsydnones in dry xylene. The structural identities of these compounds were confirmed on the basis of IR, NMR, mass spectral, and X-ray analysis.

The reductive coupling of alcohols (I) with nitroarenes (II) in refluxing toluene leads to imines (III), whilst the use of xylene as solvent gives rise to corresponding amines (IV).

The [5+1] annulation of enamidines, which were prepared from functionalized silanes, organolithium compounds and two nitriles, with N,N-dimethylformamide dialkyl acetals as the C1 unit is described, leading to the synthesis of tri- and tetrasubstituted pyrimidine derivatives under catalyst- and solvent-free reaction conditions. Furthermore, the [5+1] annulation of enamidines by using orthoesters as the C1 unit is described, in which catalytic amounts of ZnBr(2) catalyze the annulation to produce polysubstituted pyrimidines under toluene or xylene reflux conditions. Moreover, the combination of a reductive ring-opening reaction with [Mo(CO)(6)] and a subsequent intramolecular cyclization with tBuOK effectively causes a skeletal transformation from the pyrimidines containing an isoxazolyl and an ethoxy substituent to form pyrido[2,3-d]pyrimidin-5-one frameworks in excellent yield.

Friedel–Crafts acylation of benzene derivatives such as anisole, toluene, and xylene has been successively carried out using silver nitrate as the catalyst in the presence of an eco friendly solvent (ethyl alcohol). Both benzoyl chloride and acetyl chloride reacted smoothly under the conditions to afford the corresponding ketones in good yield.

Polarization and apparent dipole moments of a series of symmetrical molecules were determined by the standard method in three solvents: benzene, p -xylene, and mesitylene. Their explanation by complex formation with solvent applies only in the case of 1,4-dicyanobenzene and 4,4’-dicyanobiphenyl since the apparent orientation polarizations ( P O.app ) are large and depend strongly on solvent. On the other hand, 1,4-dihalogenbenzenes do not form any complexes and P O.app is virtually zero. 1,4-Dihalogenbicyclo[2,2,2]octanes reveal also considerable P O.app which is attributed mainly to enhanced atomic polarization but – in the case of heavier halogens – also partly to complexes of unknown structure.

The conversion of meta -xylene has been investigated over offretites with different levels of ion exchange. The ratio isomerization/disproportionation increases with the degree of exchange, most probably due to an increased accessibility of the reactant to the internal surface and to a higher number and strength of acid sites. The addition of a hydrogenation function, in H 2 atmosphere, slightly increases the activity and decreases the deactivation as a function of time. The conversion of 1−3-dimethylcyclohexene-1 yields experimental evidence that a bifunctional path exists for the reaction in these conditions. The supposed intermediate olefin isomerizes and disproportionates faster than meta -xylene, but the ortho/para selectivity remains unchanged.

Toluene, labeled with {sup 14}C in either the methyl position or uniformly in the aromatic ring, did not undergo a measurable amount of either ring expansion-contraction or ring degradation to produce ethene at temperatures up to 350{degrees}C. Ethylbenzene dealkylation and disproportionation and xylene isomerization occur to produce equilibrium mixtures of diethylbenzenes or xylenes under these reaction conditions; hence, ring expansion-contraction must be much slower than these isomerization reactions.

Using deuterated para-xylene as a reactant we have found that more than 20% of the meta- and ortho-xylenes, obtained when using a HY zeolite as catalyst, are formed via a bimolecular mechanism. This involves, as an intermediate complex, a molecule of trimethylbenzene and another of xylene. The bimolecular process is less important in the case of mordenite, and does not occur in Zeolite Beta at low levels of conversion. The relative proportion of uni- to bimolecular mechanism depends on: reaction conditions, zeolite composition, and zeolite structure. Some of the mechanistic conclusions, reached when using xylene isomerization and transalkylation as a test reaction on faujasite zeolites, should be revised in light of these results. Finally, transalkylation between trimethylbenzenes and xylenes is proposed as a test reaction for 12 membered-ring (MR) zeolites since structural differences can be better established than when the conventional xylene isomerization-transalkylation reaction is used.

Zinc chloride-catalyzed rearrangement of 1-N-allylindoline and 1-N-(2-methylallyl)indoline proceeds readily in refluxing xylene to give 7-allylindoline and 7-(2-methylallyl)indoline in 73 % and 86 % yields, respectively. The reaction of 1-N-2-butenylindoline and zinc chloride give rise to the mixture of 7-(1-methylallyl)indoline, 7-(cis- and trans-1-methyl-1-propenyl)indoline, and 7-(trans-2-butenyl)indoline. On the other hand, the similar reaction of 1-N-(3-methyl-2-butenyl)indoline with zinc chloride led to the formation of a mixture of 1,2,5,6-tetrahydro-4,4-dimethyl-4H-pyrrolo[3,2,1-ij]quinoline and 7-(3-methyl-2-butenyl)indoline

Dielectric relaxation measurements have been performed on the four isomers 2,2′ -, 2,3′ -, 3.3′ - and 2,4′ -difluorodiphenyl (DFDP) in p -xylene in the frequency and temperature ranges of 1.5–10 GHz and 293–323 K respectively. It has been found that symmetrically substituted derivatives (2,2′ - and 3,3′ -difluorodiphenyls) show a Debye-like pattern and that for non-symmetrically substituted derivatives (2,3′ - and 2,4′ -DFDP) the dielectric absorption differs strongly from this type of pattern. According to the model, this behaviour indicates that in the symmetrical compounds the contribution of the intramolecular rotation can be neglected and that in the case of non-symmetrically substituted derivatives there are two dielectric relaxations connected with internal rotation and overall molecular reorientation respectively. The analysis of the dielectric relaxation times together with moments of inertia is used to obtain further information about the molecular dynamics.

3-Oxo-2,3-dihydrobenzofuran reacted with ethyl 2-cyano-3-ethoxypropenoate, methyl 2-cyano-3-methoxy-propenoate affording compounds 3 (2-(2-cyano-2-alkoxycarbonylvinyl)-3-hydroxybenzofuran) obtained as a mixture of Z + E isomers. Methyl 2-methoxycarbonyl-3-methoxypropenoate gave compound 4. Malonic compounds added on 2-dimethylaminomethylene-3-oxo-2,3-dihydrobenzofuran 6 for giving compound 3 or 2-oxo-3-methoxycarbonyl-2H-pyrano[3,2-b]benzofuran 8. Compound 8 was also obtained by heating compound 4 in xylene.

Thermolysis reactions of the exo (distal) and endo (proximal) isomers of 7-vinyl-6b,8,8a-tetrahydrocyclobut[a]acenaphthylen-7-ol (1a and 1b) have been studied, both in refluxing xylene and in a packed pyrolysis column. These epimers were prepared from the corresponding cyclobutanone (3). An oxy-Cope rearrangement of 1b was not observed under any conditions. Both epimers gave the same thermolysis products, a fused cyclohexanone derivative 15 (a formal [1,3] shift product) and vinyl ketone 16 (a retro-ene product). At temperatures above 250 °C some acenaphthylene was also obtained. The anionic oxy-Cope variant gave only 15. A common diradical intermediate is proposed for the thermal reactions.

The reaction of benzimidazolium salt (3) and polarized olefins (1a,b,d and 2c) with K 2 CO 3 in CHCl 3 gave the corresponding benzimidazolium N-allylides (4a-d). Thermolyses of N-allylides (4a,b) in refluxing xylene afforded the 1,5-dipolar cyclization product, benzopyrroloimidazole (5a), whereas heating of N-allylides (4c,d) resulted in back-donated 1,6-cyclization to give the mesomeric betaines, benzimidazopyridiniumides (7a,b). Treatment of 3 and 2a with K 2 CO 3 in CHCl 3 yielded directly benzopyrroloimidazole (5b), while similar treatment of 3 with 1c or 2b gave benzopyrrolopyrazines (6a,b)

Treatment of N-(diphenylphosphinyl)-3-aryl-1-phenyl-2-propenimines with p-toluenesulfonic acid in heated xylene provided 4-aryl-2,6-diphenylpyridines and 4-aryl-3-arylmethyl-2,6-diphenylpyridines via an unprecedented dimerization reaction of the 2-propenimine.

The reaction of ethyl diazoacetate with 1-(methylthio)-3,4-dimethylphosphole 1-sulfide (6) in refluxing xylene leads to a corresponding diene-carbene [2+1] cycloadduct (7). The stereochemistry of 7 was established by X-ray crystal structure analysis. Compound 7 is converted into 2-(ethoxycarbonyl)-4,5-dimethylphosphinine upon reaction with triphenyl phosphite at 160°C

The side-chain alkylation of p -xylene with methanol has been studied on alkali cation exchanged and impregnated zeolites. The results show that the activities and the selectivities for p -ethyltoluene and p -methylstyrene formation are correlated with the acid—base properties of the catalysts which are characterized by poisoning with phenol and infrared (IR) spectra of adsorbed acetic acid or pyridine. IR spectra show that there are absorption bands of acetate on all used alkali cation zeolites and pyridine adsorbed sites on LiX and NaX zeolites. It is also shown that the activities of the reaction increase when the catalysts are modified by copper or silver oxide. ESCA (electron spectroscopy for chemical analysis) results indicate that, under the reaction conditions, copper or silver oxide is present in its reduced state which can catalyze the dehydrogenation of methanol to formaldehyde, and give a promoting role for the side-chain alkylation.

Fluoride ion-induced desilylation of 1-methyl-1-(trimethylsilyl)methyl-2-(2-substituted phenyl)pyrrolidinium (3a), -piperidinium (3b and 3c), and -perhydroazepinium iodides (3d and 3e) gave high yields of eight- (5a), nine- (5b and 5c), and ten-membered cyclic amines (5d, 5e, 6d and 6e), containing conjugated-triene bond systems. These triene products are intermediates in the Sommelt-Hauser rearrangement of cyclic 1-methyl-2-phenylammonium 1-methylides (4), and were isomerized to the corresponding Sommelet-Hauser rearrangement products (7) in the presence of a strong base or an acid (except for 5b). Heating of these trienes in xylene yielded mixtures of the Stevens rearrangement products (8) and ring-opened amines (9). Selective formation of 8 was achieved by ultraviolet irradiation of the trienes (5) in hexane. The reaction mechanisms are discussed.

The Catalytic properties of ISI-1, 3, 4, 5 and 6, synthesized in mixtures of water and organic solvent, have been studied. Although having acidic properties similar to a sample of ZSM-5 zeolite comprising small and aggregated crystallites, the five zeolites showed low selectivities for C 5 + product and fraction of aromatics in the C 5 + product in syngas-to-gasoline and methanol-to-gasoline reactions. Under methanol-to-gasoline reaction conditions, ISI-3, 4, 5 and 6 showed a high production of p -xylene in the xylene product. From the results of physicochemical measurements, the unique Catalytic properties of each ISI zeolite can be attributed to its crystal structure, pore size and large crystallite size.

A series of new metallo-macrocycles with a furan, pyridine, terphenyl, and xylene moiety has been synthesized.

The cycloaddition reaction of 3-methoxycabonyl-2H-cyclohepta[b]furan-2-one with 6,6-dimethylfulvene was carried out under refluxing in ethanol, benzene, or xylene. The [4+2] cycloadduct was formed as a major product in ethanol or benzene together with the minor [8+2] cycloadduct. On the other hand, the [8+2] cycloadduct was formed as a single product in xylene. The [4+2] cycloadduct was completely changed to the [8+2] cycloadduct under refluxing in xylene by a retro–Diels–Alder reaction, a re-cycloaddition reaction followed by spontaneous decarboxylation. The structure of the [8+2] cycloadduct was clearly confirmed by chemical transformation to methyl 3-isopropyl-1H-cyclopent[a]azulene-9-carboxylate which was obtained by the hydride reduction of methyl 3-isopropylidene-3H-cyclopent[a]azulene-9-carboxylate.

The preparation of a novel macrocyclic compound, tetrahydroxy[3.1.3.1]metacyclophane 5 by base-catalysed condensation of 1,3-(2,2′-dihydroxy-5,5′-di-tert-butyldiphenyl) propane 4 with formaldehyde in xylene in 90% yield is described and its conformational properties are discussed.

The desirable reaction of ethylbenzene dealkylation, accompanied by xylene isomerisation, has been studied over MFI zeolite. The effects of variation in ethylbenzene concentration in the isomer feed and the presence of paraffinic compounds on the dealkylation have been considered. Also, the undesired dealkylation of ethylbenzene during its alkylation is reported. The extent of dealkylation depends on the weight hourly space velocity, temperature and mole ratio of alkylbenzene to alcohol. The suppression of the undesired dealkylation during alkylation is discussed.

Solid acid catalysts with acid strength of -14.52 0 2 SO 4 or mixing of the boehmite samples with anhydrous aluminum sulfate, in both cases followed by calcination in nitrogen at 650 °C. The catalysts were characterized by measurements of surface area, adsorption of pyridine and benzene, acid strength measurements by the indicator method and by catalytic activity tests in the isomerization of cyclohexene, p -xylene and n-hexane. Properties of the catalysts prepared by both methods were comparable.

The diffusion, adsorption, and reaction of xylenes on HSZM-5 was investigated by means of time-resolved in situ FTIR spectroscopy and gas chromatography. The different diffusion coefficients determined for the three sylene isomers (p:o:m ≍ 1000:10:1) were found to influence the isomerization rate above 523 K under the reaction conditions employed. Below that temperature, reactant diffusion played a minor role. For all xylene molecules, the intramolecular mechanism of isomerization suffices to account for all observations. The selectivity of m-xylene isomerization was found to depend primarily upon the transition entropy (transition state selectivity). The selectivity in o- and p-xylene depends upon the surface concentration of the primary product, m-xylene. Its concentration is a function of the activity of the catalyst and the diffusional constraints m-xylene faces. The decrease of the effectiveness of ZSM-5 above 523 K due to reactant diffusional constraints can be seen in lower coverages of m- and o-xylene in comparison to p-xylene.

The alkylation of toluene with methanol and the isomerization of xylene were investigated separately and in detail on zeolite H-ZSM-5 as catalyst. The influence of crystal size alone on rates and product distributions was studied for two Si/Al ratios in the zeolite at 573 and 723 K in a gradientless batch-reactor. The isomer distribution in the xylene resulting from toluene methylation is constant from zero up to at least 50% conversion of the methanol in a stoichiometric mixture, H-ZSM-5 being always para-selective. para-Xylene prevails increasingly in the products when either crystal size, temperature, or Al content in the zeolite increase; essentially pure p-xylene can be obtained in the limit with unmodified H-ZSM-5 as catalyst. The rate of isomerization of xylene alone to an equilibrium mixture of isomers was found to be roughly proportional to the extent of the (external) surface of the zeolite crystals, the ratios of the rates of different reactions in the triangular scheme of isomerization being nearly independent of crystal size. The observations can be understood as resulting from the interaction of reaction an diffusion in the volume of the crystals. 34 refs., 11 figs., 4 tabs.

The novel macrocyclic compounds hexahydroxy[2.1.2.1.2.1]- (7b) and octahydroxy[2.1.2.1.2.1.2.1]metacyclophane (7c) have been prepared from anisole in six steps by using the tert-butyl function as a positional protective group on the aromatic ring. Base-catalyzed condensation of 1,2-bis(5-tert-butyl-2-hydroxy-phenyl)ethane (5) with formaldehyde in refluxing xylene does not afford the dimeric product, tetrahydroxy[2.1.2.1]metacyclophane 6a, but furnishes the larger macrocycles 6b and 6c in 70–90% yield. AlCl3/MeNO2-catalyzed trans-tert-butylation of 6b and 6c in toluene gives the desired metacyclophanes 7b and 7c in 60 and 80% yields, respectively, along with tert-butyltoluene 8b. The conformations of the systems such as trimer 6b and tetramers 6c, 7c have been evaluated from their dynamic 1H-NMR spectra. The tetramer 6c is fixed to form a “pleated-loop” conformation like the calix[8]arenes due to the much more stronger intramolecular hydrogen bonding among the hydroxyl groups than in the trimer 6b.

From cis-2-(p-methylbenzoyl)-1-cyclohexanecarboxylic acid (1) and dien- do-3-(p-methylbenzoyl)bicyclo[2.2.1]heptane-2-carboxylic acid (2) with α,ω-alkylenediamines, the perhydroimidazo[2,1-a]isoindolone (3), the corresponding perhydropyrimido and perhydrodiazepino derivatives (4) and (5) and their methylene-bridged tetracyclic analogues (6-8) were obtained. Compound (1) and ethanolamine yielded the perhydro-1,3-oxazo- lo [2,3-a]isoindolone derivative (9), while (1) with 3-amino-1-propanol or 2-aminoethanethiol gave the homologous saturated 1,3-oxazino deriva- tive (10) and thiazoloisoindolone derivative (11), respectively. On boiling in xylene, (9) was transformed to the hydroxyethylisoindolone (12). From (1) and o-phenylenediamine, the trans-isoindolo[2,1-a]benzi- midazole derivative (13) was formed, while (1) and o-aminothiophenol gave the partly saturated cis-benzthiazole analogue (14)

Michacl-type addition of diethyl phosphoramidate to α,β-unsaturated esters occurs when the reactants are refluxed in toluene or xylene with an excess of potassium carbonate in the presence of tetrabutyl-ammonium bromide (TBABr). Dephosphorylation of methyl and ethyl acrylate adducts leads to the respective β-alanine esters.

Perchloroheptafulvene (4) is prepared by photoisomerization of perchloro-p-xylene (1) in a surprising and key-step solid-state ring-expansion reaction yielding perchloro-1-methyl-1,3,6-cycloheptatriene (9), followed by dechlorination of 9 with SnCl 2 -2H 2 O. X-ray analyses of 9 and 4 are reported and discussed in relation to the already known crystal structure of xylene 1 suggesting that in the first step the strained molecular geometry of 1 assists its ring expansion

Transformation of commercial C 7 and C 9 aromatic streams to xylenes over zeolite beta have been studied. These results have been compared with those obtained on other zeolites like ZSM-5 and mordenite. The effect of variations in reaction parameters like temperature, weight hourly space velocity (WHSV) and feed composition on xylene formation was considered. The trimethylbenzenes became disproportionated, while ethyltoluenes underwent de-ethylation followed by disproportionation of product toluene. The highest yield of xylenes was obtained with a feed consisting of nearly equal proportions of toluene and 1,3,5-trimethylbenzene. Lower WHSV and higher temperature enhanced the formation of xylenes.

Bromide promoted decompn. of tert-Bu bromide in the presence of triphenylphosphine gives, besides isobutene, hydrogen(triphenyl)phosphonium bromide. When heated to approx. 150 DegC in the presence of xylene, the latter salt liberates hydrogen bromide which may then be trapped in an aprotic solvent such as di-Et ether. [on SciFinder (R)]

An excellent method of preparation of N-aryl-enamino esters (4) was achieved by developing N-N exchange reaction of an N-methyl-enamino ester (6) with di- and trimethoxyanilines (3). Thermolysis of 4 in xylene gave di- and trimethoxy-4-quinolones (7) in excellent yields

n -Pentane and o -xylene isomerizations have been studied at 285 and 150°C, respectively, on seven dealuminated H-mordenites containing different amounts of framework and nonframework aluminum which were prepared by steaming or calcining NH 4 -mordenite. The number of Bronsted and Lewis sites were known beforehand from 29 S high-resolution magnetic resonance and infrared study of low-temperature CO adsorption. In addition, the availability of the acid sites to the reactants was estimated from the ratios of the liquid monolayer volume of the reactant ( n -pentane or o -xylene) to that of N 2 , the availability of the active sites to N 2 and CO being the same. It was observed that the initial rates of isomerization divided by the number of available Bronsted sites are proportional to the number of available Lewis sites. This observation suggests a synergistic enhancement of the acidity by the interaction between Bronsted and Lewis acid centers. Other aspects related with the products distribution are also discussed.

Base-catalyzed condensation of 1,2-bis[5-tert-butyl-3-(5-tert-butylsalicyl)-2-hydroxyphenyl]ethane (8) with formaldehyde in xylene affords a novel ethylene-bridged calixarene-analogous macrocyclic metacyclophane. However, not the desired 2 has been obtained. Instead, the novel macrocyclic compounds pentahydroxy[2.1.2.1.1]- (9) and hexahydroxy-[2.1.1.1.1.1]metacyclophane (10) have been isolated in 35 and 25% yields, respectively. The mechanism for the above disproportionation occurring during the base-catalyzed condensation of 8 to afford these macrocyclic metacyclophanes and their 1H-NMR spectral behavior are discussed.

1-(N,N-Diaroyl)amino-4-phenyl-1,2,3-triazol-5-yl-methyltriphenylphosphonium bromide 2 reacted with potassium t -butoxide or triethylamine in dry toluene giving the very stable phosphorus ylide 5 . Refluxing of 5 in xylene gave the unexpected 3-aroyl-6-arylpyrazolo[4,3- d ][2,3]benzodiazepines 6 by a Dimroth-like rearrangement of the triazole ring and a 1,7-electrocyclization of the nitrilimine intermediate 11 . When the xylene solution was not rigorously refluxed the 3(5)-aroyl-5(3)-phenyl pyrazole 7 was isolated. The x-ray crystal structures of compounds 5d and 6b are also given.

The reaction of phosphates 1 and 5 and thiophosphates 3 and 7 gave the olefins 2 and 6 with 0.8 – 1.6 mol eq of Lawesson's reagent in xylene at reflux. Compounds 1, 3, 8, 5 and 7 gave 2 and 6 in better yields with a small amount of AgOTf (0.1 – 0.3 mol eq) even in toluene at reflux.

Starting from readily available methyl 5-methyloxazole-4-carboxylate (1) and 4-methyl-5-oxazolylcar-boxylic acid hydrazide (11) the title compounds were prepared. The reaction of compound 1 with hydrazine hydrate afforded the corresponding hydrazide 2. The reaction of compound 2 with formic acid yielded 1-formyl-2-(5-methyloxazole-4-carboxyl)hydrazine (3). Refluxing of the latter with phosphorus pentasulfide in xylene gave compound 5 in 62% yield. The reaction of compound 3 with phosphorus pentoxide afforded compound 4. Starting from hydrazide 11, compounds 13 and 14 were prepared similarly. Reaction of compound 2 with substituted isothiocyanate yielded compound 9 which was cyclized in basic medium to 4-alkyl-5-(5-methyl-4-oxazolyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione (10). The isomer 19 was prepared similarly. Methylation and subsequent oxidation of compound 19 gave compound 21. Reaction of the acid 7 with thiosemicarbazide in the presence of phosphorus oxychloride gave 2-amino-5-(5-methyl-4-oxazolyl)1,3,4-thiadiazole (8). 2-Amino-5-(4-methyl-5-oxazolyl)-1,3,4-thiadiazole (17) was prepared from acyl chloride 15 by the usual method.

Dialkyl malonate esters reacted with P 2 S 5 S 8 in boiling xylene and with 2-mercaptobenzothiazole ZnO as catalyst to yield 5-alkylthio-3H-1,2-dithiole-3-thiones as major products.

N-bridged 1,3-thiazolium-4-olates were synthesized by reaction of 3-substituted 3-aminothioacrylanilides with bromoacetic acid ethyl ester in refluxing xylene. Their structural aspects were investigated by means of mass, NMR, and absorption spectroscopy. They display an unusual ring-chain tautomeric equilibrium, which is governed by the nature of the solvents and thepH value.

In the present work a novel improved and convenient procedure for the synthesis of oxazoles has been developed. Acetamide, instead of ammonium acetate, was used to react with phenacyl benzoates in boiling xylene in the presence of BF 3 Et 2 O as the catalyst. According to this new synthetic route, nine oxazole compounds were readily prepared as single products in reasonably high yields. On the basis of the experimental results, a plausible mechanism of this reaction is proposed.

Bis(oxazolines), disubstituted in the 4 and 5 positions, are synthesized from dimethylmalonyl bis-diamides of the suitable 1,2-disubstituted chiral aminoethanol. Starting from the same diamide, the ring closure can be realized either with retention (reflux in xylene with dibutyl tin dichloride - the Masamune protocol) or inversion (conversion into the mesylate and reflux with aqueous ethanolic NaOH) of the configuration at the chiral center in position 5.