Regioselective construction of six-membered fused heterocyclic rings via Pd/C-mediated C-C coupling followed by iodocyclization strategy: a new entry to 2H-1,2-benzothiazine-1,1-dioxides

We describe a practical and elegant method of constructing a thiazine ring fused with benzene under mild reaction conditions. A variety of 4-iodo-2H-benzo[e][1,2]thiazine-1,1-dioxides were prepared with high regioselectivity via a two-step process involving Pd/C-mediated C-C coupling of o-halobenzenesulfonamides with terminal alkynes, followed by iodocyclization of the resulting o-(1-alkynyl)arenesulfonamide using elemental iodine in acetonitrile. The coupling reaction was carried out using 10% Pd/C-PPh₃-CuI as a catalyst system in the presence of Et₃N. The process worked well for bromides and iodides, and a wide array of terminal alkynes containing alkyl and aryl substituents were employed. The iodocyclization step tolerated a variety of functional groups such as hydroxy, chloro, cyano, and methoxy, producing the six-membered heterocyclic ring selectively. The resulting 4-iodo-2H-benzo[e][1,2]thiazine-1,1-dioxides participated in Sonogashira, Heck, and Suzuki reactions producing a wide range of functionally substituted benzothiazines in good yields.     

Diethyl ethoxymethylenemalonate in triheterocycles: A new synthesis of pyrido[3,2-e]pyrimido[1,2-c]pyrimidines

Diethyl ethoxymethylenemalonate was used for the novel synthesis of the triheterocyclic 3-carbethoxy-9,ll-disubstituted-4-oxo-4H-pyrido[3,2-e]pyrimido[1,2-c]pyrimidines from 4-aminopyrido[2,3-d]pyrim-idines via thermal cyclization of the intermediate ethyl 2-carbethoxy-3-[5,7-disubstituted-4-amino-pyrido[2,3-d]pyrimidin-4-yl]acrylates. The alkaline hydrolysis of 3-carbethoxy-4-oxo-4H-pyrido[3,2-e]-pyrimido[1,2-c]pyrimidines was performed to give corresponding acid derivatives.     

Synthesis of 1-methyl-7-(trifluoromethyl)-1H-pyrido[2,3-c][1,2]thiazin-4(3H)-one 2,2-dioxide

The reaction of methyl 2-bromo-6-(trifluoromethyl)-3-pyridinecarboxylate ( 1 ) with methanesulfonamide gave methyl 2-[(methylsulfonyl)amino]-6-(trifluoromethyl)-3-pyridine-carboxylate ( 2 ). Alkylation of compound 2 with methyl iodide followed by cyclization of the resulting methyl 2-[methyl(methylsulfonyl)amino]-6-(trifluoromethyl)-3-pyridinecarboxylate ( 3 ) yielded 1-methyl-7-(trifluoromethyl)-1H-pyrido[2,3-c][1,2]thiazin-4(3H)-one 2,2-dioxide ( 4 ). The reaction of compound 4 with α,2,4-trichlorotoluene, methyl bromopropionate, methyl iodide, 3-trifluoromethylphenyl isocyanate, phenyl isocyanate and 2,4-dichloro-5-(2-propynyloxy)phenyl isothiocyanate gave, respectively, 4-[(2,4-dichlorophenyl)methoxy]-1-methyl-7-(trifluoromethyl)-1H-pyrido[2,3-c][1,2]thiazine 2,2-dioxide ( 5 ), methyl 2-[[1-methyl-2,2-dioxido-7-(trifluoromethyl)-1H-pyrido[2,3-c][1,2]thiazin-4-yl]oxy]propanoate ( 6 ), 1,3,3-trimethyl-7-(trifluoromethyl)-1H-pyrido[2,3-c][1,2]thiazin-4(3H)-one 2,2-dioxide ( 7 ), 4-hydroxy-1-methyl-7-(trifluoromethyl)-N-[3-(trifluoromethyl)phenyl]-1H-pyrido[2,3-c][1,2]thiazine-3-carboxamide 2,2-dioxide ( 8 ), 4-hydroxy-1-methyl-7-(trifluoromethyl)-N-phenyl-1H-pyrido[2,3-c][1,2]thiazine-3-carboxamide 2,2-dioxide ( 9 ) and N-[2,4-dichloro-5-(2-propynyloxy)phenyl]-4-hydroxy-1-methyl-7-(trifluoromethyl)-1H-pyrido[2,3-c][1,2] thiazine-3-carboxamide 2,2-dioxide ( 10 ).     

Thienopyrimidines. VII. Reactions of the 4-hydrazinothieno[2,3-d]pyrimidines

The cyclization reactions of the 4-hydrazinothieno[2,3-d]pyrimidines give s-triazolo[1,2-c]-thieno[3,2-e]pyrimidines and tetrazolo[1,5-c]thieno[3,2-e]pyrimidines.     

Fotochromic Dihetarylethenes: XIX. Synthesis of 1,2-Dihetarylethenes with 2,5-Dihydrothiophene Bridge from Thieno[3,2-b]pyrroles

Reductive cyclization by McMurry method was performed with diketosulfide obtained by treating with Na₂S of compound prepared by regioselective acylation of methyl 2-methyl-4H-thieno[3,2-b]pyrrole-5-carboxylate with chloroacetyl chloride. As a result was synthesized a photochromic 1,2-dihetarylethene where the fuzed rings are connected by a 2,5-dihydrothiophene ring. The oxidation of the latter provides 2,5-dihydrothiophene-1,1-dioxide bridge.     

New method for the synthesis of substituted thieno[3,2-b]pyridines and 5H-pyrano[2,3-d]thieno[3,2-b]pyridines derived from them

A new highly selective method was developed for the synthesis of substituted thieno[3,2-b]-pyridines based on the domino reaction of monopotassium salt (rather than dipotassium one) of carbamoylcyanodithioacetic acid with ethyl 4-chloroacetoacetate. Substituted 5H-pyrano[2,3-d]-thieno[3,2-b]pyridines were synthesized based on these thieno[3,2-b]pyridines.     

Synthesis and Structure of 4-Indolyl-5-(thieno[3,2-<Emphasis Type="Italic">b</Emphasis>]pyrrol-6-yl)imidazoles

A procedure was proposed for regioselective acylation of methyl 2-methyl-4H-thieno[3,2-b]-pyrrole-5-carboxylate with 2-(3-indolyl)-2-oxoacetyl chloride. Reactions of the resulting methyl 6-[2-(3-indolyl)-1,2-dioxoethyl]-2-methyl-4H-thieno[3,2-b]pyrrole-5-carboxylate with aromatic aldehydes and ammonium acetate in acetic acid afforded the corresponding methyl 6-[2-aryl-4-(3-indolyl)imidazol-5-yl]-2-methyl-4H-thieno[3,2-b]pyrrole-5-carboxylates. The structure of methyl 6-[2-(4-chlorophenyl)-4-(3-indolyl)imidazol-5-yl]-2-methyl-4H-thieno[3,2-b]pyrrole-5-carboxylate was studied by X-ray analysis.     

Synthesis of Benzofuro[3,2-e][1,4]diazepines

A synthesis of 4-N-oxides and of 3-hydroxy derivatives of 1,3-dihydro-2H-benzofuro[3,2-e][1,4]diazepin-2-ones and of 2,3-dihydro-1H-benzofuro[3,2-e][1,4]diazepines is described. Condensation of 2-acetyl- and 2-benzoyl-3-ethoxycarbonylaminobenzofurans with acrylonitrile gave derivatives of 1,2-dihydro- and of 1,2,3,4-tetrahydrobenzofuro[3,2-b]pyridine.     

Synthesis of 7H-tetrazolo[1,5-c]pyrrolo[3,2-e]pyrimidines and their reductive ring cleavage to 4-aminopyrrolo[2,3-d]pyrimidines

Some new 7,9-disubstituted 7H-1,2,3,4-tetrazolo[1,5-c]pyrrolo[3,2-e]pyrimidines 5 have been synthesized either by diazotization of 4-hydrazino-5,7-disubstituted-7H-pyrrolo[2,3-d]pyrimidines 4 obtained by hydrazinolysis of 4-chloro-5,7-disubstituted-7H-pyrrolo[2,3-d]pyrimidines 3 or via a substitution reaction between 3 and sodium azide. 5,7-Disubstituted-7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 2 were obtained by cyclocondensation of 2-amino-3-cyano-1,4-disubstituted pyrroles 1 with formic acid which on chlorination using phosphorus oxychloride afforded 3 . A novel route for the synthesis of 4-amino-5,7-disubstituted-7H-pyrrolo[2,3-d]pyrimidines 6 by the reductive ring cleavage of 5 has been reported.     

Five-membered 2,3-dioxoheterocycles: LXXXVI. Spiro-heterocyclization of 1-aryl-4-aroyl-5-methoxycarbonyl-1H-pyrrole-2,3-diones under the action of 3-arylamino-1H-inden-1-ones. Crystal and molecular structure of 4′-hydroxy-3′-(2,4-dimethylbenzoyl)-1,1′-diphenyl-1H-spiro[indeno[1,2-b]pyrrole-3,2′-pyrrole]-2,4,5′(1′H)-trione

1-Aryl-4-aroyl-5-methoxycarbonyl-1H-pyrrole-2,3-diones react with 3-arylamino-1H-inden-1-ones affording 1,1??-diaryl-3??-aroyl-4??-hydroxy-1H-spiro[indeno[1,2-b]pyrrole-3,2??-pyrrole]-2,4,5??(1??H)-triones. The crystal and molecular structure of 4??-hydroxy-3??-(2,4-dimethylbenzoyl)-1,1??-diphenyl-1H-spiro[indeno[1,2-b] pyrrole-3,2??-pyrrole]-2,4,5??(1??H)-trione.     

Novel heterocycles. Synthesis of 2,3-dihydro-6-methyl-2-phenyl-4H,6H-pyrano[3,2-c][2,1]benzothiazin-4-one 5,5-dioxide and related compounds

The reaction of 2-chloro-4-(methylsulfonyl)benzoyl chloride ( 5 ) with 1-methyl-1H-2,1-benzothiazin-4-(3H)-one 2,2-dioxide ( 4 ) gave the O-benzoyl compound, 1-methyl-2,2-dioxido-1H-2,1-benzothiazin-4-yl 2-chloro-4-(methylsulfonyl)benzoate ( 6 ), which rearranged to give the C-benzoyl isomer, [2-chloro-4-(methylsulfonyl)phenyl] (4-hydroxy-1-mefhyl-2,2-dioxido-1H-2,1-benzothiazin-3-yl)methanone ( 7 ). The O-cinnamoyl compound 13 that resulted from the addition of 2,4-dichlorocinnamoyl chloride ( 11 ) to compound 4 rearranged to give the C-cinnamoyl compound, 3-(2,4-dichlorophenyl)-1-(4-hydroxy-1-methyl-2,2-dioxido-1H-2,1-benzothiazin-3yl)-2-propen-1-one ( 15 ). On the other hand, 1-methyl-2,2-dioxido-1H-2,1-benzothiazin-4-yl 3-phenyl-2-propenoate ( 19 ) (from cinnamoyl chloride ( 17 ) and compound 4 ) rearranged to give 2,3-dihydro-6-methyl-2-phenyl-4H,6H-pyrano[3,2-c][2,1]benzothiazin-4-one 5,5-dioxide ( 21 ), an example of a hitherto unknown ring system. Additional examples of this novel heterocycle were prepared from 1-methyl-7-(trifluoromethyl)-1H-pyrido[2,3-c][1,2]thiazin-4(3H)-one 2,2-dioxide ( 23 ) and 1-methyl-1H-thieno[3,2-c][1,2]thiazin-4(3H)-one 2,2-dioxide ( 8 ).     

Intramolecular 4+2 cycloaddition of thieno[2,3-e][1,2,4]triazines: routes towards condensed thieno[2,3-b]pyridines

Synthetic approaches towards new condensed thienopyridine ring systems including furo[2,3-b]thieno[3,2-e]pyridines, bisthieno[2,3-b:3′,2′-e]pyridines, 5H-chromeno[2,3-b]thieno[3,2-e]pyridines, 5H-benzo(f)chromeno[2,3-b]thieno[3,2-e]pyridines have been achieved by application of intramolecular 4+2 cycloaddition reactions of suitably designed thieno[2,3-e][1,2,4]triazines tethered with alkene or alkyne terminals.     

Formation and Ring Contraction of Benzo[f][1,2]Thiazepine-1,1-Dioxides from and to Benzo[e][1,2]Thiazine-1,1-Dioxides

Alkoxide-promoted ring expansion of the novel ethyl 2-(6,7-dimethoxy-3-oxo-3,4-dihydrobenzo[e][1,2]thiazine-1,1-dioxide-2-yl)acetate 3a and analogous 4,4-diethyl derivative 3b and cyclization of methyl 2-[2-(phenylaminocarbonylmethyl sulfamoyl)-4,5-dimethoxyphenyl] acetate 9 to the corresponding new 3-carboxylates and 3-carboxanilide of 7,8-dimethoxy-4-hydroxy-2,5-dihydrobenzo[f][1,2]thiazepine-1,1-dioxide (5a,b and 10 respectively) is described. Compound 5a was deacylated upon treatment with sodium hydroxide followed by hydrochloric acid to give 7,8-dimethoxy-2,3-dihydrobenzo[f][1,2]thiazepine-1,1-dioxide-4 (5H)-one 8 and its N-ethyl derivative transferred to 6,7-dimethoxy-2-ethyl-3-oxo-3,4-dihydrobenzo[e][1,2]thiazine-1,1-dioxide 7 by the reaction with ethyl methyl ketone in the presence of pyrrolidine.     

A convenient route to diazepines by intramolecular cyclisation of carbonylazides

The appropriate substituted carbonylazides I treated with warm acetic acid give the corresponding acetamide IV or the cyclic lactam VI . This is a convenient route to 10,11-Dihydro-5H-pyrrolo[1,2-a][1,4]-benzodiazepin-11-one and 10,11-Dihydro-4H-thieno[2,3-e]pyrrolo[1,2-a][1,4]diazepin-10-one.     

Synthesis of novel spiro[indole-3,3′-pyrrolidin]-2(1H)-ones

Diastereoselective [3+2] cycloaddition of azomethine ylide to 1,3-dimethyl-6-(2-oxo-1,2-dihydro-3H-indol-3-ylidene)-3a,9a-diphenyl-3,3a,9,9a-tetrahydroimidazo[4,5-e]thiazolo[3,2-b]-[1,2,4]triazine-2,7(1H,6H)-dione yields hitherto unknown 1,1′,3-trimethyl-3a,9a-diphenyl-3,3a,9,9a-tetrahydrodispiro(imidazo[4,5-e]thiazolo[3,2-b][1,2,4]triazine-6,3′-pyrrolidine-4′,3″-indole)-2,2″,7(1H,1″H)-triones.     

Synthesis of novel spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones via three component reaction

A new and efficient method for the synthesis of hitherto unreported spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones was developed via the Domino Knoevenagel condensation–Michael addition–intermolecular cyclization sequences of isatin derivatives, cyclohexane-1,3-diones, and 2-hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones, employing 12-tungstophosphoric acid (H₃PW₁₂O₄₀) as an effective and inexpensive catalyst.     

6H-indeno[1,2-b]pyrido[3,2-e]pyrazines. A new heterocyclic ring system

Condensation of 1,2-indanedione and 1,2,3-indanetrione hydrate (ninhydrin) with 2,3-diamino-pyridines gave a number of compounds belonging to the hitherto unknown 6H-indeno[1,2-b]-pyrido[3,2-e]pyrazine ring system. The unsymmetrical nature of the reactants can theoretically result in isomeric ring closure products. Assignment of the 6H- ring system was based upon the identity of 6H-indeno[1,2-b]pyrido[3,2-e]pyrazin-6-one obtained from 2,3-diaminopyridine and ninhydrin with material prepared by unequivocal synthesis. The direction of cyclization of ninhydrin and 1,2-indanedione with the diamines was shown to be the same by reduction of the indenopyridopyrazinones to the corresponding indenopyridopyrazines. Some physical, chemical, and tumor growth-inhibitory properties of the products are reported.     

Synthesis of 3H-thieno[3,2-c]-1,2-dithiole-3-thione and its reaction with n-butylamine

A convenient synthesis of 3H-thieno[3,2-c]-1,2-dithiole-3-thione (7) is proposed. The reaction of 7 with n-butylamine afforded the N-butylthieno[3,2-c]isothiazole-3(2H)-thione (7a) in dynamically equilibrium [1] with its 3H-thieno[3,2-c]-1,2-dithiole-N-butyl-3-imino isomer 7b. Characterizations and antimicrobial activities of the synthesized products are reported.     

Synthesis of new condensed thieno[2,3-b]pyridines containing pyrimidine and imidazole rings

Two different convenient methods have been developed for the synthesis of condensed thieno[2,3-b]pyridines. The intramolecular cyclization of 3-amino-2-hydrazinocarbonyl-7,7-dimethyl-7,8-dihydo-5H-pyrano[3,4-e]-thieno[2,3-b]pyridine was carried out to give 7,7-dimethyl-2-oxo-1,2,6,7-tetrahydro-9H-pyrano[3′,4′-e]-imidazo[4″,5″∶2,3]thieno[5,4-b]pyridine, which is the first representative of a new heterocyclic system.     

Efficient synthesis of 5,6-dihydro-8H-[1,2,4]thiadiazino[6,5,4-de]phenanthridine 4,4-dioxide and 5,6-dihydro-8H-[1,2,4]-thiadiazino[6,5,4-ij]thieno[2,3-c]quinoline 4,4-dioxide

A new efficient and versatile synthesis to obtain different substituted 5,6-dihydro-8H-[1,2,4]thiadiazino[6,5,4-de]phenanthridine 4,4-dioxide and 5,6-dihydro-8H-[1,2,4]-thiadiazino[6,5,4-ij]thieno[2,3-c]quinolone 4,4-dioxide was developed. The four cyclic systems are achieved by a three-step synthesis proceeding under mild conditions in high yields.