Synthesis and reactions of halo-, nitro-, and arylazo-substituted 3-aminotropolones. Formation of 8H-cyclohept[d]oxazol-8-one derivatives

3-Acetamidotropolone ( 1a ) reacted with bromine and fuming nitric acid to afford respectively 3-acetamido-7-bromo- ( 1b ) and -5,7-dibromotropolone ( 1c ) and 3-acetamido-5-nitrotropolone ( 1d ). Azo-coupling reaction of 1a gave 3-acetamido-5-(4-methylphenylazo)tropolone ( 1f ). Bromination of 1d and 1f gave 7-bromo-substituted compounds 1e and 1g , respectively. The compounds 1b-g were hydrolyzed to afford 3-aminotropolones 4b-g , which reacted with triethyl orthoformate to give the corresponding 8H-cyclohept[d]oxazol-8-ones 5b-g . Heating of 3-acetamidotropolones 1a-d with polyphosphoric acid gave 2-methyl-8H-cyclohept[d]oxazol-8-ones 6a-d .     

Synthesis and reactions of halo-, nitro-, and arylazo-substituted 3-cinnamoyltropolones. Formation of styryl-substituted heterocycle-fused troponoid compounds

3-Cinnamoyltropolone ( 1 ) reacted with bromine to afford 7-bromo- ( 2 ), 5,7-dibromo-3-cinnamoyltropolone ( 3 ), and 6,8-dibromo-4,9-dihydrocyclohepta[b]pyrane-4,9-dione ( 4 ) according to amount of the reagent. Iodination and nitration of 1 gave respectively 7-iodo- ( 5 ) and 5-nitro-3-cinnamoyltropolone ( 6 ). Azo-coupling reactions gave 5-arylazo-3-cinnamoyltropolones 7a-f . Compounds 1, 2, 3 and 5 reacted with hydroxylamine to give 3-styryl-8H-cyclohept[d]isoxazol-8-ones 10-13 , while 6 and 7a gave 5-nitro-3-styryl-8H-cyclohept[d]-isoxazol-8-one oxime ( 14 ) and 2-cinnamoyl-7-methoxy-4-phenylazotropone ( 15 ), respectively. The reactions of 1,3 , and 5 with phenylhydrazine gave 3-styryl-1,8-dihydrocycloheptapyrazol-8-ones 16-19 .     

Studies with quinolines: New synthetic routes to 4H,5H,6H,9H‐benzo[ij]pyrano[2,3‐b]quinolizine‐8‐one, 4H‐pyrano[2,3‐b]pyridine, 2H‐pyran‐2‐one and pyranopyridoquinoline derivatives

Several new benzo[ij]pyrano[2,3‐b]quinolizine‐8‐ones 5 and 4H‐pyrano[2,3‐b]pyridine 8 derivatives were synthesized from 4‐hydroxyquinolines 1 . Reacting 3‐acetyl‐4‐hydroxy‐1‐phenyl‐1H‐quinoline‐2‐one with dimethylformamide dimethylacetal afforded 3‐(3‐Dimethylarnino‐acryloyl)‐4‐hydroxy‐1‐phenyl‐1H‐quinolin‐2‐one 9 . This reacted with hippuric acid and diethyl 3‐oxoglutarate to give 2H‐pyran‐2‐one 13 and pyranopyridoquinoline 17 respectively.     

2-[3-(Trifluoromethyl)phenyl]furo[3,2-b]pyrroles: synthesis and reactions

The synthesis and reactions of methyl 2-[3-(trifluoromethyl)phenyl]-4H-furo[3,2-b]pyrrole-5-carboxylate (1a) are described. Upon reaction with methyl iodide, benzyl chloride, or acetic anhydride, this compound gave N-substituted products 1b-d. By hydrolysis of compounds 1a-c, the corresponding acids 2a-c were formed, or by reaction with hydrazine-hydrate, the corresponding carbohydrazides 3a-c were formed. By heating 2-[3-(trifluoromethyl)phenly]-4H-furo[3,2-b]pyrrole-5-carboxylic acid (2a) in acetic anhydride, 4-acetyl-2-[3-(trifluoromethyl)phenyl]furo[3,2-b]pyrrole (4) was formed. By hydrolysis of 4, 2-[3-(trifluoromethyl)phenyl]-4H-furo[3,2-b]pyrrole (5a) was formed, and reactions with methyl iodide or benzyl chloride gave N-substituted products 5b-c. The reaction of 4 with dimethyl butynedioate gave substituted benzo[b]furan 6. Compound 3a reacted with triethyl orthoesters giving 7a-c, which afforded with phosphorus (V) sulphide the corresponding thiones 8a-c. The thiones 8a-c reacted with hydrazine hydrate to form hydrazine derivatives 9a-c. The reaction of triethyl orthoformiate with compounds 9a-c led to furo[2′,3′: 4,5]pyrrolo[1,2-d][1,2,4]triazolo[3,4-f][1,2,4]triazines 10a-c. Hydrazones 11a-c were formed from 3a-c and 5-[3-(trifluoromethyl)phenyl]furan-2-carboxaldehyde. The effect of microwave irradiation on some condensation reactions was compared with “classical” conditions. The results showed that microwave irradiation shortens the reaction time while affording comparable yields.     

Efficient synthesis of 2‐substituted thieno[2,3‐d]pyrimidin‐4(3H)‐ones via an iminophosphorane

The carbodiimides 4 , obtained from reactions of iminophosphorane 3 with aromatic isocyanates, were reacted with secondary amines to give 2‐dialkylamino‐5‐ethyl‐6‐methyl‐thieno[2,3‐d]pyrimidin‐4(3H)‐ones 6 in the presence of catalytic amount of EtONa. Reactions of 4 with phenols or ROH in the presence of the catalytic amount of K2CO₃ or RONa gave 2‐aryloxy‐ or 2‐alkoxy‐5‐ethyl‐6‐methyl‐thieno[2,3‐d]pyrimidin‐4(3H)‐ones 6 in satisfactory yields. The effects of the nucleophiles on cyclization have been investigated. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:266–270, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20424     

Synthesis and reactions of halo-, nitro-, and arylazo-substituted 3-acetyltropolones. Formation of heterocycle-fused troponoid compounds

3-Acetyltropolone ( 1 ) reacted with bromine, iodine, and nitric acid to afford respectively 3-acetyl-5,7-di-bromotropolone ( 2 ), 3-acetyl-7-iodotropolone ( 3 ), and 3-acetyl-5-nitro- ( 4 ) and 3-acetyl-5,7-dinitrotropolone ( 5 ). Azo-coupling reactions of 1 gave 3-acetyl-5-arylazotropolones 7a-f. The Schmidt reactions of 2 and 3 gave respectively 5,7-dibromo- ( 9 ) and 7-iodo-2-methyl-8H-cyclohept[d]oxazol-8-one ( 10 ), while 4 gave 3-acetamido-5-nitrotropolone ( 11 ). Compounds 2 and 4 reacted with hydroxylamine to give 3-methyl-8H-cyclohept[d]isoxazol-8-ones 12 and 13. The reactions of 2 , 3 , and 4 with hydrazine gave 3-methyl-1,8-dihydrocycloheptapyrazol-8-ones 15 , 16 , and 17.     

Simple and Efficient Synthesis of Novel 3‐Substituted 2‐Thioxo‐2,3‐dihydro‐1H‐benzo[g]quinazolin‐4‐ones and Their Reactions with Alkyl Halides and α‐Glycopyranosyl Bromides

A series of 3‐substituted 2‐thioxo‐2,3‐dihydro‐1H‐benzo[g]quinazolin‐4‐ones 4a – e were synthesized from the reaction of 3‐aminonaphthalene‐2‐carboxylic acid 1 with isothiocyanate derivatives 2a – e . The alkylation of 4a – e with alkyl halides gave 3‐substituted 2‐alkylsulfanyl‐2,3‐dihydro‐1H‐benzo[g]quinazolin‐4‐ones 5a – o . S‐Glycosylation was carried out via the reaction of 4a – e with glycopyranosyl bromides 7a and 7b under anhydrous alkaline conditions. The structure of the compounds was established as S‐nucleoside and not N‐nucleoside. Conformational analysis has been studied by homonuclear and heteronuclear two‐dimensional NMR methods (2D DFQ‐COSY, heteronuclear multiple quantum coherence, and heteronuclear multiple bond correlation). The S site of alkylation and glycosylation was determined from the ¹H and ¹³C heteronuclear multiple quantum coherence experiments.     

A convenient synthesis of (z)-3-(α-alkoxycarbonyl-α-cyanomethylene)-2-oxo-1,2,3,4-tetrahydroquinoxalines and related compounds

(Z)-3-(α-Alkoxycarbonyl-α-cyanomethylene)-2-oxo-1,2,3,4-tetrahydroquinoxalines 3 and (Z)-3-(α-alkoxycarbonyl-α-cyanomethylene)-3,4-dihydrobenzo[g]quinoxalin-2(1H)-ones 5 possessing various alkoxycarbonyl groups were prepared in good yields directly from the reaction of dialkyl (E)-2,3-dicyanobutendioates 1 with o-phenylenediamine ( 2 ) or with 2,3-diaminonaphthalene ( 4 ), respectively. Furthermore, 2,3-diaminopyridine ( 6 ) and 3,4-diaminopyridine ( 7 ) were reacted with the diethyl ester 1b to give (Z)-2-(α-cyano-α-ethoxycarbonylmethylene)-1,2-dihydro-4H-pyrido[2,3-b]pyrazin-3-one ( 8 ) and (Z)-3-(α-cyano-α-ethoxycarbonylmethylene)-3,4-dihydro-1H-pyrido[3,4-b]pyrazin-2-one ( 9 ), respectively. The structural studies of 3, 5, 8 , and 9 were carried out by nmr experiments in some details.     

Investigation on the condensation of α and β ketoaldehydes with hydroxyaromatic compounds

Mechanism of the condensation reactions of methylglyoxal, phenylglyoxal and benzoylacetaldehyde with phenolic compounds have been discussed. It was observed that the reaction mechanisms changed depending on the type of the phenolic and also dicarbonyl compounds. While, methylglyoxal gave the angular methyl derivative of naphthofuraranonaphthofuran with 2‐naphthol, phenylglyoxal and its p‐chloro and p‐methoxy derivatives formed benzo[b]naphtho[2,1‐f]oxepine‐13‐ones. However, resorcinol behaved different and gave 2‐phenyl‐3‐(2,4‐dihydroxy)‐6‐hydroxy‐benzo[b]furans with phenylglyoxal derivatives. 2‐Phenyl‐4‐(2‐hydroxynaphmyl)‐4H‐naphtho[b]pyran was produced from the reaction of benzoylacetaldehyde and 2‐naphthol, but the reaction product was 3,9‐dihydroxy‐6‐phenyl‐6,12‐methano‐12H‐dibenzo[1,3]dioxocin when the same carbonyl compound reacted with resorcinol.     

Radical Cyclization Reactions via Manganese(III) Acetate Leading to 2‐Thienyl‐Substituted Dihydrofuran Compounds

The 2‐thienyl‐substituted 4,5‐dihydrofuran derivatives 3 – 8 were obtained by the radical cyclization reaction of 1,3‐dicarbonyl compounds 1a – 1f with 2‐thienyl‐substituted conjugated alkenes 2a – 2e by using [Mn(OAc)₃] (Tables 1–5). In this study, reactions of 1,3‐dicarbonyl compounds 1a – 1e with alkenes 2a – 2c gave 4,5‐dihydrofuran derivatives 3 – 5 in high yields (Tables 1–3). Also the cyclic alkenes 2d and 2e gave the dihydrobenzofuran compounds, i.e., 6 and 7 in good yields (Table 4). Interestingly, the reaction of benzoylacetone (=1‐phenylbutane‐1,3‐dione; 1f ) with some alkenes gave two products due to generation of two stable carbocation intermediates (Table 5).     

Synthesis of 1-substituted-2,3,4,9-tetrahydro-(2-oxopropyl)-1H-pyrido [3,4-b] indoles and their base-catalyzed rearrangements to N- [2-[2-(1-alkyl-3-oxobutenyl)-1H-indol-3-yl] ethyl]acetamides

The condensation of 1H-indole-3-ethanamides, 1 , with 2,4-pentanediones, 2 , gave enamines 3 . Acid catalyzed ring closure of 3 gave 1-(1-substituted-2,3,4,9-tetrahydro- (2-oxopropyl) -1H-pyrido [3,4-b] indoles 4 . Subsequent N-acetylation yielded 5 which sequentially produced 2,3-disubstituted indoles 6 and 7 resulting from C? N bond cleavage after treatment with sodium alkoxide in ethanol. Controlled catalytic hydrogenation of the latter gave saturated derivatives 8 and 9 .     

Pyrimidine derivatives. VII. Nucleophilic reactions of 5-bromo-1-(bromoalkyl)-6-bromomethyl-2,4(1H,3H)-pyrimidinediones

The reactions of 1-(bromoalkyl)-5-bromo-6-bromomethyl-3-methyl-2,4(1H,3H)-pyrimidinedione (1) with several nucleophiles were examined as follows: by reaction with sodium methoxide, 6-(bismethoxy)methyl-5-debrominated derivatives 2, 3 , and 4 were prepared; the corresponding di-substituted compounds (side chains in 1-and 6-positions) 5, 6, 7 , and 9 were obtained by treatment with silver nitrate, silver acetate, potassium thiocyanate, and potassium thioacetate; the reaction with thioacetamide and iso-butylamine gave bicyclic compounds [1,4]thiazino[4,3-c]- 11 , pyrazino[1,2-c]- 12 , and [1,4]diazepino[1,2-c]pyrimidinedione 13 , respectively; pyrrolidine, morpholine, and sodium azide afforded the corresponding 6-substituted compounds 14, 15 , and 16 .     

Directed regiospecificity of 1,3-dipolar cycloaddition of 2-diazopropane to 4- and 5-substituted pyridazin-3(2H)-ones

6-Methoxy-2-methylpyridazin-3(2H)-one ( 1 ) gave with 2-diazopropane ( 8 ) a mixture of 3H-pyrazolo[3,4-d]-pyridazin-4(5H)-one derivative 12 , as the main product, and -7(6H)-one derivative 10 , as the minor product. On the other hand, 4-substituted pyridazin-3(2H)-ones 2, 3 , and 4 gave 3H-pyrazolo[3,4-d]pyridazin-7(6H)-one 10 , exclusively, while 5-substituted pyridazin-3(2H)-ones 5, 6 , and 7 produced only the isomeric 3H-pyrazolo[3,4-H]pyridazin-4(5H)-one 12 . The 5-phenylsulfonyl derivative 13 gave with 8 by elimination of a molecule of nitrogen, followed by rearrangement, 1,2-diazepine derivative 15 and with an excess of 8 3H-pyrazolo[3,4-d][1,2]diazepine derivative 16. 1 ,2-Dimethylpyridazine-3,6-(1H,2H)-dione and its derivatives 18 and 19 produced 3H-pyrazolo[3,4-d]pyridazine-4,7(5H,6H)-dione derivative 23 , while from 17 and 1-diazoindane ( 24 ) the spiro compound 27 was obtained. The 1,2-dihydro and 3a,7a-dihydro intermediates 21 and 25 were isolated.     

Synthesis of pyrimidino[4,5-b][1,5]benzodiazepin-2-ones and pyrimidino[1,6-a]benzimidazol-1-ones from 4-ethoxycarbonylamino-1H-1,5-benzodiazpine-3-carbonitrile via 4-(2-aminoanilino)pyrimidin-2(1H)-one-5-carbonitriles

Reactions of 4-ethoxycarbonylamino-1H-1,5-benzodiazepine-3-carbonitrile (2) with aliphatic primary amines gave 1-substituted 4-(2-aminoanilino)pyrimidin-2(1H)-one-5-carbonitriles 3. Analogous reactions of 2 with aromatic primary amines afforded 2-(2′-anilino-1′-cyanovinyl)benzimidazoles 5 and 6. Upon treatment with triethylamine, 3 underwent intramolecular cyclization to give 3-substituted 5-aminopyrimidino[4,5-b]-[1,5]benzodiazepin-2(3H,11H)-ones 8 . Heating of 3 with p-toluenesulfonic acid in ethanol gave 2-substituted pyrimidino[1,6-a]benzimidazol-1(2H)one-4-carbonitriles 9 . Reactions of 2 with hydrazines were also described. Mechanistic pathways are proposed to account for the products.     

Regioselective 1,3‐Dipolar Cycloadditions of (1Z)‐1‐(Arylmethylidene)‐5,5‐dimethyl‐3‐oxopyrazolidin‐1‐ium‐2‐ide Azomethine Imines to Acetylenic Dipolarophiles

The 5,5‐dimethylpyrazolidin‐3‐one ( 4 ), prepared from ethyl 3‐methylbut‐2‐enoate ( 3 ) and hydrazine hydrate, was treated with various substituted benzaldehydes 5a – i to give the corresponding (1Z)‐1‐(arylmethylidene)‐5,5‐dimethyl‐3‐oxopyrazolidin‐1‐ium‐2‐ide azomethine imines 6a – i . The 1,3‐dipolar cycloaddition reactions of azomethine imines 6a – h with dimethyl acetylenedicarboxylate (=dimethyl but‐2‐ynedioate; 7 ) afforded the corresponding dimethyl pyrazolo[1,2‐a]pyrazoledicarboxylates 8a – h , while by cycloaddition of 6 with methyl propiolate (=methyl prop‐2‐ynoate; 9 ), regioisomeric methyl pyrazolo[1,2‐a]pyrazolemonocarboxylates 10 and 11 were obtained. The regioselectivity of cycloadditions of azomethine imines 6a – i with methyl propiolate ( 9 ) was influenced by the substituents on the aryl residue. Thus, azomethine imines 6a – e derived from benzaldehydes 5a – e with a single substituent or without a substituent at the ortho‐positions in the aryl residue, led to mixtures of regioisomers 10a – e and 11a – e . Azomethine imines 6f – i derived from 2,6‐disubstituted benzaldehydes 5f – i gave single regioisomers 10f – i .     

Highly Efficient [3 + 2] Cycloaddition: Click Synthesis of Novel 1H‐indol‐3‐yl‐benzo[d]imidazole Bis‐triazoles

A series of novel 1‐((1H‐1,2,3‐triazol‐4‐yl)methyl)‐2‐(1‐((1H‐1,2,3‐triazol‐4‐yl)methyl)‐5‐substituted‐1H‐indol‐3‐yl)‐6‐substituted‐1H‐benzo[d]imidazoles 5a – i have been prepared using click chemistry as an ideal strategy where [3 + 2] cycloaddition of azides with terminal alkynes has been developed as the target compounds. In route‐II, 5‐substituted‐1H‐indole‐3‐carbaldehydes 1a – c react with 5‐substituted orthophenylenediamine 8 to give desired products, that is, 6‐substituted‐2‐(5‐substituted‐1H‐indol‐3‐yl)‐1H‐benzo[d]imidazole 6a – i . Here, 6a – i react with 2 equiv of propargylbromide 7 to give novel 6‐substituted 2‐(5‐substituted‐1‐(prop‐2‐yn‐1‐yl)‐1H‐indol‐3‐yl)‐1‐(prop‐2‐yn‐1‐yl)‐1H‐benzo[d]imidazole 4a – i . 4a – i were reacted with 2 equiv of NaN₃ in t‐butanol/water (1:2) and add catalytic amount of CuSO₄.5H₂O. Stir the reaction mixture at room temperature to get the target products 5a – i . Here, obtained products contain four rings, that is, one indole, two triazoles, and one benzimidazole. The main advantages of this method are short reaction times, easy workup, higher yields (88–92%), and no by‐products formation.     

Formation of 18e− and 16e− Acyl(η3‐cyclooctenyl)rhodium(III) Complexes in the Reaction of Cationic (Cycloocta‐1,5‐diene)rhodium(I) Compounds with 2‐(Diphenylphosphino)benzaldehyde

The reaction of cationic diolefinic rhodium(I) complexes with 2‐(diphenylphosphino)benzaldehyde (pCHO) was studied. [Rh(cod)₂]ClO₄ (cod=cycloocta‐1,5‐diene) reacted with pCHO to undergo the oxidative addition of one pCHO with (1,2,3‐η)cyclooct‐2‐en‐1‐yl (η³‐C₈H₁₃) formation, and the coordination of a second pCHO molecule as (phosphino‐κP)aldehyde‐κO(σ‐coordination) chelate to give the 18e⁻ acyl(allyl)rhodium(III) species [Rh(η³‐C₈H₁₃)(pCO)(pCHO)]ClO₄ (see 1 ). Complex 1 reacted with [Rh(cod)(PR₃)₂]ClO₄ (R=aryl) derivatives 3 – 6 to give stable pentacoordinated 16e⁻ acyl[(1,2,3‐η)‐cyclooct‐2‐en‐1‐yl]rhodium(III) species [Rh(η³‐C₈H₁₃)(pCO)(PR₃)]ClO₄ 7 – 10 . The (1,2,3‐η)‐cyclooct‐2‐en‐1‐yl complexes contain cis‐positioned P‐atoms and were fully characterized by NMR, and the molecular structure of 1 was determined by X‐ray crystal diffraction. The rhodium(III) complex 1 catalyzed the hydroformylation of hex‐1‐ene and produced 98% of aldehydes (n/iso=2.6).     

Syntheses of 6-Amino-1-(β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]-1,3-oxazin-4-one,an isostere of oxanosine,and the guanosine analog 6-amino-1-(β-d-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one via ring closure of pyrazole-5-thioureido intermediates

6-Amino-1-(β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]-1,3-oxazin-4-one ( 4 ), an isostere of the nucleoside antibiotic oxanosine has been synthesized from ethyl 5-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)pyrazole-4-carboxylate ( 6 ). Treatment of 6 with ethoxycarbonyl isothiocyanate in acetone gave the 5-thioureido derivative 7 , which on methylation with methyl iodide afforded ethyl 1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-5-[(N'-ethoxycarbonyl-S-methylisothiocarbamoyl)amino]pyrazole-4-carboxylate ( 8 ). Ring closure of 8 under alkaline media furnished 6-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]-1,3-oxazin-4-one ( 10 ), which on deisopropylidenation afforded 4 in good yield. 6-Amino-1-(β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one ( 5 ) has also been synthesized from the AICA riboside congener 5-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)pyrazole-4-carboxamide ( 12 ). Treatment of 12 with benzoyl isothiocyanate, and subsequent methylation of the reaction product with methyl iodide gave 1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-5-[(N'-benzoyl-S-methylisothiocarbamoyl)amino]pyrazole-4-carboxamide ( 15 ). Base mediated cyclization of 15 gave 6-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one ( 14 ). Deisopropylidenation of 14 with aqueous trifluoroacetic acid afforded 5 in good yield. Compound 4 was devoid of any significant antiviral or antitumor activity in culture.     

[1]Benzothienopyrimidines. II. Study of the electrophilic substitutions of [1]benzothieno[3,2-d]pyrimidine and [1]benzothieno[3,2-d]pyrimidin-4-(3H)one

The nitration and bromination of both [1]benzothieno[3,2-d]pyrimidin-4(3H)one ( 1 ) and [1]benzothieno-[3,2-d]pyrimidine ( 2 ) has been studied. Nitration of 1 at ?30° afforded a mixture of 8-nitro[1]benzothieno-[3,2-d]pyrimidin-4(3H)one ( 7b ) (70%) and 6-nitro[1]benzothieno[3,2-d]pyrimidin-4(3H)one ( 7a ) (30%). However when the nitration was carried out at 60°, the 6,8-dinitro derivative 8 was the result. On the contrary, the nitration of 2 at ?30° gave a single nitration product, 8-nitro[1]benzothieno[3,2-d]pyrimidine ( 11 ). The bromination of both 1 and 2 gave the corresponding 8-bromo derivatives 10 and 13 . Assignment of structure of all the products was based on ir and nmr spectral studies and on unequivocal syntheses.     

A Convenient Synthesis of 2,3‐Dihydro‐4H‐thiopyrano[2,3‐b]‐, ‐[2,3‐c]‐, or ‐[3,2‐c]pyridin‐4‐ones by the Reaction of the Corresponding 1‐(Chloropyridinyl)alk‐2‐en‐1‐ones with NaSH

2,3‐Dihydro‐4H‐thiopyrano[2,3‐b]pyridin‐4‐ones 4 were prepared by a three‐step sequence from commercially available 2‐chloropyridine ( 1 ). Thus, successive treatment of 1 with ⁱPr₂NLi (LDA) and α,β‐unsaturated aldehydes gave 1‐(2‐chloropyridin‐3‐yl)alk‐2‐en‐1‐ols 2 , which were oxidized with MnO₂ to 1‐(2‐chloropyridin‐3‐yl)alk‐2‐en‐1‐ones 3 . The reactions of 3 with NaSH?n H₂O proceeded smoothly at 0° in DMF to provide the desired thiopyranopyridinones. Similarly, 2,3‐dihydro‐4H‐thiopyrano[2,3‐c]pyridin‐4‐ones 8 and 2,3‐dihydro‐4H‐thiopyrano[3,2‐c]pyridin‐4‐ones 12 were obtained starting from 3‐chloropyridine ( 5 ) and 4‐chloropyridine ( 9 ), respectively.