Highly regioselective direct halogenation: a simple and efficient method for preparing 4-halomethyl-5-methyl-2-aryl-1,3-thiazoles

An unprecedented C4-methyl regioselective halogenation of 4,5-dimethyl-2-aryl-1,3-thiazoles (1) has been accomplished. The reaction of compound 1 with N-chlorosuccinimide and N-bromosuccinimide under mild conditions provides an efficient and operationally simple method for obtaining 4-chloromethyl-5-methyl-2-aryl-1,3-thiazoles (2) and 4-bromomethyl-5-methyl-2-aryl-1,3-thiazoles (3), respectively, in good yields without the formation of 4-methyl-5-halomethyl regioisomers.     

Synthesis and anti-arrhythmic activity of some piperidine-based 1,3-thiazole, 1,3,4-thiadiazole, and 1,3-thiazolo[2,3-c]-1,2,4-triazole derivatives

Abstract  The reaction of 1-[4-(piperidin-1-yl)benzylidene]thiosemicarbazide with hydrazonoyl chlorides afforded 1,3-thiazole derivatives. Cyclization of two compounds of the latter 1,3-thiazole by means of bromine in the presence of sodium acetate at room temperature gave 1,3-thiazolo[2,3-c]-1,2,4-triazole derivatives. The reaction of 2-cyano-3-(4-piperidin-1-ylphenyl)prop-2-enethioamide with hydrazonoyl chlorides under reflux in ethanol in the presence of triethylamine yielded 1,3-thiazoles. Treatment of 3-oxo-3-(piperidin-1-yl)propanenitrile with phenyl isothiocyanate in DMF, in the presence of KOH, at ambient temperature, resulted in the formation of 3-anilino-3-mercapto-2-(piperidin-1-ylcarbonyl)acrylonitrile which was reacted with hydrazonoyl chlorides to yield the corresponding 1,3,4-thiadiazole derivatives. Some of the newly synthesized compounds had significant anti-arrhythmic activity. Graphical Abstract        

5-Aryl-2-furaldehydes in the Synthesis of 2-Substituted 1,3-Benzazoles

2-[2-(5-Aryl-2-furyl)ethenyl]-1,3-benzazoles were synthesized by reaction of 5-aryl-2-furaldehydes with 2-methylbenzoxazole, 2-methylbenzothiazole, 2-methylbenzimidazole, and 2-cyanomethylbenzimidazole. The corresponding benzazoles were also obtained by reaction of N-(5-arylfurfurylidene)anilines with 2-methylbenzoxazoles and of 3-(5-aryl-2-furyl)-2-cyanopropenoyl chlorides with o-phenylenediamine. The acylation of o-aminophenol with 3-(5-aryl-2-furyl)-2-cyanopropenoyl chlorides occurs at the amino group without subsequent oxazole ring closure.     

Electrophilic benzylation of the pyridine ring. Action of benzyl chlorides on 2-amino and 2-benzylaminopyridine

The reaction of 2-aminopyridine as well as 2-benzylaminopyridine hydrochloride with benzyl chlorides used in molar ratio of 1:2 and 1:1 respectively and carried out at 250° leads via 2-benzylamino-5-benzylpyri-dines to 2-amino-5-benzylpyridines as the final products. The formation of 2-benzylamino-5-benzylpyridines did not occur in the direct C-benzylation reaction of the 2-benzylaminopyridine ring with the use of benzyl chloride. Its formation takes place via the intermediate state of 2-(N,N-dibenzylamino)pyridinium and 1-benzyl-2-benzylaminopyridinium chlorides for which the solvent separated ion-molecule form is proposed. Interaction of the ingredients of the intermediate state i.e., benzyl cation and 2-benzylaminopyridine, leads in an electrophilic mechanism to the formation of 2-benzylamino-5-benzylpyridine hydrochlorides. Thermolysis of the aminomethylene bond in 2-benzylamino-5-benzylpyridine hydrochlorides leads to the final 2-amino-5-benzylpyridines.     

Synthesis and Structure of Quaternary Salts Derived from 2-Anilino- and 2-Benzylamino-5,6-dihydro-4H-1,3-thiazine

Substituted phenacyl bromides react with 2-anilino-5,6-dihydro-4H-1,3-thiazine at the exocyclic nitrogen atom and with 2-benzylamino-5,6-dihydro-4H-1,3-thiazine at the nitrogen atom in the ring. The structure of the reaction intermediates was elucidated, and their cyclization into 1-benzyl-2-aryl-6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazinium bromides was performed.     

Synthese von (Methylthio)penam-Derivaten durch Keten-Addition an 4,5-Dihydro-5-(methylthio)-1,3-thiazole

Synthesis of (Methylthio)penam Derivatives via Keten Addition onto 4,5-Dihydro-5-(methylthio)-1,3-thiazoles The 4,5-dihydro-5-(methylthio)-2-phenyl-1,3-thiazoles 3a and 3b , easily prepared from the corresponding 1,3-thiazol-5(4H)-thiones and MeLi, react with dichloroacetyl chloride ( 5a ) and acidoacetyl chloride ( 5b ) in the presence of Et₃N to give (methylthio)penam derivatives 6 (Table 1). The reaction mechanism is either a [2 + 2] cycloaddition of in situ generated ketene or a two-step reaction (Scheme 2). The structure of 6f has been confirmed by X-ray crystallography (Fig. 2). The relative configuration of 6a-e follow from comparison of their ¹H-NMR spectra with those of 6f (Fig. 1). The 6-azidopenams 6d and 6f have been reduced to aminopenams 8a and 8b , respectively. Acylation of 8a with phenacetyl chloride yields 9 (Scheme 4).     

A Convenient Route to New 4,5-Dimercapto-1,3-thiazole Derivatives

A series of 2-X-4-tosyl-5-chloro-1,3-thiazoles (X = OH, OAlk, SH, SAlk, NH₂, NHAlk, NAlk₂, NHAr, etc.) were prepared from accessible 1-tosyl-2,2-dichloroethenyl isothiocyanate. Only some of these compounds containing a moderately labile hydrogen atom peculiarly react with thiophenols in the presence of triethylamine to give 4,5-di(arylthio)-2-(hydroxy- or arylamino)-1,3-thiazoles, which are difficult to prepare by other routes. It is quite possible that, in the course of nucleophilic substitution of the chlorine atom and tosyl residue by the corresponding arylthio groups, a significant role is played by nonaromatic tautomeric forms of functionally 2-substituted 1,3-thiazoles formed by proton transfer to positions 3 and 5 of the heteroring.     

The synthesis of hexahydrooxoepithiopyridinedicarboximides by the reaction of thioamides with N-substituted maleimides

The synthesis of hexahydrooxoepithiopyridinedicarboxyimide (5: X₂ = N-Ph) by the reaction of thioamides 1 with N-substituted maleimide ( 2a ) was examined. The reaction of primary thioamides, such as thiobenzamide and p-toluthioamide with N-phenylmaleimide gives compounds 5 together with corresponding 4-hydroxy-1,3-thiazoles 4 . However, a similar reaction of secondary thioamides, such as N-methylthioacetamide, thiobenzanilide, with N-phenylmaleimide did not provide compounds 5 without addition of acid. The reaction pathway and the configuration of 5 were also investigated.     

Reactivity of 2-deoxy-2-iodoglycosyl isothiocyanates with O-, S-, and N-nucleophiles. Synthesis of glycopyranoso-fused thiazoles

The reactivity of 2-deoxy-2-iodoglycosyl isothiocyanates toward O- and S-nucleophiles gives an easy access to 2-deoxy-2-iodoglycopyranosyl thiocarbamates and dithiocarbamates. Internal nucleophilic displacement of the iodine by the sulfur atom in these compounds allows the preparation of glycopyranoso[1,2-d]-1,3-thiazoles and glycopyranoso[1,2-d]-1,3-thiazolidin-2-one or -2-thione. Reaction with amines or polyamines as N-nucleophiles led directly to 2-aminoglycopyranoso[1,2-d]-1,3-thiazoles without isolation of the intermediate thioureas. Methyl 2-deoxy-2-iodoglycopyranosyl thiocarbamates also allow the synthesis of 2-deoxyglycopyranosyl thiocarbamates or 2-deoxy-2-iodoglycopyranosyl carbamates.     

Synthesis and Addition Reactions of 1,3-Thiazole-5(4H)-thione Oxides

1,3-Thiazole-5(4H)-thione oxides 2 were prepared by oxidation of the corresponding 1,3-thiazole-5(4H)-thiones 1 with m-chloroperbenzoic acid (Table 1). Addition reactions of 2 with organolithium and Grignard reagents yielded 4,5-dihydro-4,4-dimethyl-1,3-thiazol-5-yl methyl sulfoxides of type 4 via thiophilic attack (Table 2). Whereas the reaction with the organolithium compounds proceeded with fair-to-excellent yields, the Grignard reagents reacted only very sluggishly. The sulfoxides 4 could also be prepared via oxidation of 4,5-dihydro-4,4-dimethyl-5-(methylthio)-1,3-thiazoles of type 3 with m-chloroperbenzoic acid, together with the corresponding sulfones 5 (Scheme 1).     

Configuration and isomerization of 2,4,5-substituted 1,3,2-dioxaborinanes

Reaction of esters of isobutylboronic acid with 2-methyl-1-phenyl-1,3 propanediol and 2-benzyl-1,3-butanediol gave 2-isobutyl-5-methyl-4-phenyl- and 4-methyl-5-benzyl-1, 3, 2-dioxaborinanes respectively, with a preponderance of the cis-isomers in the mixtures. Cis-2-isobutyl-5-methyl-4-phenyl-1, 3, 2-dioxaborinane was converted to thetrans isomer on heating to 150°C with a catalytic amount of ZnCl₂.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1291–1294, September, 1995.     

Some reactions of 5-benzyl-2,3,5-trichloro-4,4-dimethoxy-cyclopent-2-en-1-one and its derivatives

5-Benzyl-2,3,5-trichloro-4,4-dimethoxycyclopent-2-en-1-one and 2-benzyl-2,4,5-trichlorocyclopent-4-ene-1,3-dione were subjected to dehydrochlorination by the action of 1,4-diazabicyclo[2.2.2]octane, selective dechlorination at C⁵ by the action of CrCl₂, and Ad_NE replacement of the chlorine atom at C³ by the action of secondary amines. The reduction of 2-benzyl-2,4-dichloro-5-morpholinocyclopent-4-ene-1,3-dione with sodium tetrahydridoborate in methanol and ethanol gave different products.     

Synthesis of substituted [1,3]thiazolo[4,5-b]pyridines and [1,3]thiazolo[4,5-d][1,2,3]triazines

In this work, we described an easy preparation of substituted 4-amino-5-cyano-1,3-thiazoles. These compounds have been used as starting materials to obtain two classes of compounds. New substituted [1,3]thiazolo[4,5-e]pyridines were synthesized in one step via Friedländer reaction. Diazotation of 4-amino-5-cyano-1,3-thiazoles afforded 4-chloro[1,3]thiazolo[4,5-d][1,2,3]triazines in one step. The later was substituted by a secondary amine to obtain substituted 4-amino[1,3]thiazolo[4,5-d][1,2,3]triazines.     

Stereoselective O-glycosylation reactions using glycosyl donors with diphenylphosphinate and propane-1,3-diyl phosphate leaving groups

Glycosyl donors having a diphenylphosphinate and a propane-1,3-diyl phosphate leaving group were easily prepared by the addition of the anomeric hydroxyl group of 2,3,4,6-tetra-O-benzyl-α,β-d-glucopyranose to diphenylphosphinic and propane-1,3-diyldioxyphosphoryl chlorides. These glycosyl donors were selectively glycosylated with a number of primary and secondary oxygen nucleophiles in the presence of trimethylsilyl triflate (TMSOTf). The use of 1,3-diyl phosphate resulted in the stereoselective formation of β-O-linked glycosides.     

A convenient method for the synthesis of 2-[(5-benzyl-1,3-thiazol-2-yl)imino]-1,3-thiazolidin-4-one derivatives

It was found that the reaction of 2-chloroacetamido/chloropropioamido-5-benzylthiazole with potassium thiocyanate gave, via rearrangement, 2-[(5-benzyl-1,3-thiazol-2-yl)imino]-1,3-thiazolidin-4-ones.     

New thiourea organocatalysts and their application for the synthesis of 5-(1H-indol-3-yl)methyl-2,2-dimethyl-1,3-dioxane-4,6-diones a source of chiral 3-indoylmethyl ketenes

The stereoselective properties of modified thiourea organocatalysts were tested in the Friedel–Crafts alkylation of indole with 5-arylidene-2,2-dimethyl-1,3-dioxane-4,6-diones, which produces chiral 5-((1H-indol-3-yl)(aryl)methyl)-2,2-dimethyl-1,3-dioxane-4,6-diones. Based on a tentative reaction mechanism for ((S)-N-benzyl-2-(3-(3,5-bis(trifluoromethyl)phenyl)thioureido)-N,3,3-trimethylbutanamide organocatalysts, modifications were applied in four selected regions. Systematic structure-stereoselectivity relationship study allowed designing the best efficient organocatalyst for the investigated Friedel–Crafts alkylation of indole with 5-arylidene-2,2-dimethyl-1,3-dioxane-4,6-diones.     

Chlorination of isothiocyanates. VIII. Reaction of S-chloroisothiocarbamoyl chlorides with aliphatic and cycloaliphatic ketones

Reported is the synthesis of various derivatives of 2-imino-5-chloro-1,3-oxathiolanes, 2-imino-1,3-oxathioles and 1,3-thiazolin-2-ones from N-aryl- and N-alkyl-S-chloroisothiocarbamoyl chlorides and ketones.     

Characteristics of the Synthesis of Substituted and Condensed 2-Methyl-1,3-diazoles

Condensation of aliphatic and carbocyclic α-bromo ketones with thioacetamide in ethanol usually leads to substituted or condensed 2-methyl-1,3-thiazoles. However in a number of cases the required compounds are only obtained in pyridine. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, 1244–1249, August, 2005.     

Synthesis of fluoroalkyl-containing 1,2,3-triketone 2-hetarylhydrazones and their reactions with hydrazines

Fluoroalkyl-containing 1,2,3-triketone 2-(2,3-dimethyl-5-oxo-1-phenyl-1,2-dihydropyrazol-4-yl)-, 2-(4-ethoxycarbonylpyrazol-3-yl)-, and 2-(1,2,4-triazol-3-yl)hydrazones were synthesized by the azo coupling reactions of fluorinated 1,3-diketones with the corresponding hetaryldiazonium chlorides. The hetarylhydrazones thus synthesized were subjected to cyclocondensation with hydrazines at the 1,3-dicarbonyl fragment to give 3-fluoroalkyl-4-hetarylazopyrazoles.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2478–2483, November, 2004.     

Cyclization of ethyl endo-5-norbornene-2-carboxylate with hetarene sulfenyl chlorides

Cyclization of ethyl endo-5-norbornene-2-carboxylate with 1,3-benzothiazole-2-sulfenyl and 3-methoxycarbonylpyridine-2-sulfenyl chlorides follows two directions, namely, electophilic lactonization of unsaturated ester or polar cycloaddition of sulfenylating reagent to the multiple bond accompanied by ring closure by the nitrogen atom of the thiohetaryl fragment.