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.     

Synthesis of 2,3‐Diaryl‐3H‐pyrrolo[2,3‐c]pyridin‐3‐ol Derivatives by the Reaction of Aryl(3‐isocyanopyridin‐4‐yl)methanones with Aryl Grignard Reagents

The reaction of aryl(3‐isocyanopyridin‐4‐yl)methanones 1 , easily prepared from commercially available pyridin‐3‐amine, with aryl Grignard reagents gave, after aqueous workup, 2,3‐diaryl‐3H‐pyrrolo[2,3‐c]pyridin‐3‐ols 2 . These rather unstable alcohols were O‐acylated with Ac₂O in pyridine in the presence of a catalytic amount of 4‐(dimethylamino)pyridine (DMAP) to afford the corresponding 2,3‐diaryl‐3H‐pyrrolo[2,3‐c]pyridin‐3‐yl acetates 3 in relatively good yields.     

One‐Pot Synthesis of 3‐Alkoxy‐2,3‐dihydro‐1H‐isoindol‐1‐ones by the Reactions of 2‐(Azidomethyl)benzoates with NaH

A new and facile method for the general preparation of 3‐alkoxy‐2,3‐dihydro‐1H‐isoindol‐1‐ones has been developed. Thus, the reaction of 2‐(azidomethyl)benzoates with NaH affords, after workup with H₂O, 3‐alkoxy‐2,3‐dihydro‐1H‐isoindol‐1‐ones 2 . 2‐Substituted 3‐alkoxy‐2,3‐dihydro‐1H‐isoindol‐1‐ones 4 can be obtained by adding alkyl halides prior to workup with H₂O.     

Cyclization vs. Elimination Reactions of 5‐Aryl‐5‐hydroxy 1,3‐Diones: One‐Pot Synthesis of 2‐Aryl‐2,3‐dihydro‐4H‐pyran‐4‐ones

2‐Aryl‐2,3‐dihydro‐4H‐pyran‐4‐ones were prepared in one step by cyclocondensation of 1,3‐diketone dianions with aldehydes. The use of HCl (10%) for the aqueous workup proved to be very important to avoid elimination reactions of the 5‐aryl‐5‐hydroxy 1,3‐diones formed as intermediates. The TiCl₄‐mediated cyclization of a 2‐aryl‐2,3‐dihydro‐4H‐pyran‐4‐one with 1,3‐silyloxybuta‐1,3‐diene resulted in cleavage of the pyranone moiety and formation of a highly functionalized benzene derivative.     

Synthesis of 2‐Aryl‐2,3‐dihydro‐3‐sulfanyl‐1H‐isoindol‐1‐ones by Pummerer‐Type Cyclization of N‐Aryl‐2‐(sulfinylmethyl)benzamides

An efficient method for the synthesis of 2‐aryl‐2,3‐dihydro‐3‐sulfanyl‐1H‐isoindol‐1‐ones 1 via Pummerer‐type cyclization of N‐aryl‐2‐(sulfinylmethyl)benzamides 2 is described. Thus, treatment of these sulfinyl‐benzamides 2 , easily prepared from 2‐(bromomethyl)benzoates 3 in three steps, with Ac₂O at ca. 100° resulted in the formation of the desired isoindolones 1 in generally good yields.     

Hydriodic Acid‐Mediated Cyclization of α‐Substituted Secondary 2‐Ethenylbenzamides: Synthesis of 2‐Substituted 2,3‐Dihydro‐3,3‐dimethyl‐1H‐isoindol‐1‐ones and 3,3‐Disubstituted (E)‐1‐(Arylimino)‐1,3‐dihydroisobenzofurans

A new and facile method for the preparation of 2‐substituted 2,3‐dihydro‐3,3‐dimethyl‐1H‐isoindol‐1‐ones 3 and 3,3‐disubstituted (E)‐1‐(arylimino)‐1,3‐dihydroisobenzofurans 6 has been developed. Thus, treatment of N‐alkyl(or aryl)‐2‐(1‐methylethen‐1‐yl)benzamides 2 with concentrated hydriodic acid (HI) in MeCN at room temperature afforded 3 . Similar treatment of N‐aryl‐2‐(1‐phenylethen‐1‐yl)benzamide 5 with concentrated HI at 0° afforded 6 .     

Synthesis,Characterization and Crystal Structure of Some Novel 1‐Aryl‐2‐Thioxo‐2,3‐Dihydro‐1H‐Quinazolin‐4‐Ones

The base catalyzed intramolecular nucleophilic cyclization of 1‐(2‐haloaroyl)‐3‐aryl thioureas ( 1a‐i ), in the presence of DMF afforded the 1‐aryl‐2‐thioxo‐2,3‐dihydro‐1H‐quinazolin‐4‐ones ( 2a‐i ). The structures were confirmed by spectroscopic data, elemental analyses and in case of the 2c by single crystal X‐ray diffraction data. The mechanistic studies support an intramolecular nucleophilic substitution (S_NAr mechanism) rather than intramolecular aromatic substitution (S_RN1 mechanism).     

Reduction of 3‐Aminoquinoline‐2,4(1H,3H)‐diones and Deamination of the Reaction Products

3‐Aminoquinoline‐2,4‐diones were stereoselectively reduced with NaBH₄ to give cis‐3‐amino‐3,4‐dihydro‐4‐hydroxyquinolin‐2(1H)‐ones. Using triphosgene (=bis(trichloromethyl) carbonate), these compounds were converted to 3,3a‐dihydrooxazolo[4,5‐c]quinoline‐2,4(5H,9bH)‐diones. The deamination of the reduction products using HNO₂ afforded mixtures of several compounds, from which 3‐alkyl/aryl‐2,3‐dihydro‐1H‐indol‐2‐ones and their 3‐hydroxy and 3‐nitro derivatives were isolated as the products of the molecular rearrangement.     

Cp2ZrCl2‐catalyzed synthesis of 2‐substituted quinozolin‐4(3H)‐ones

Zirconocene dichloride (Cp₂ZrCl₂) in the presence of DMF was found to be a highly efficient catalyst for the synthesis of structurally diverse 2‐substituted quinozolin‐4(3H)‐ones by reaction of anthranilimide with a wide range of aryl aldehydes. Copyright © 2013 John Wiley & Sons, Ltd.     

Three‐Step Synthesis of 3‐Aryl‐2‐sulfanylthieno[2,3‐b]‐, ‐[2,3‐c]‐, or ‐[3,2‐c]pyridines from the Corresponding Aryl(halopyridinyl)methanones

A convenient three‐step procedure for the synthesis of three types of 3‐aryl‐2‐sulfanylthienopyridines 4, 8 , and 12 has been developed. The first step of the synthesis of thieno[2,3‐b]pyridine derivatives 4 is the replacement of the halo with a (sulfanylmethyl)sulfanyl group in aryl(2‐halopyridin‐3‐yl)methanones 1 by successive treatment with Na₂S?9 H₂O and chloromethyl sulfides to give aryl{2‐[(sulfanylmethyl)sulfanyl]pyridin‐3‐yl}methanones 2 . In the second step, these were treated with LDA (LiNⁱPr₂) to give 3‐aryl‐2,3‐dihydro‐2‐sulfanylthieno[2,3‐b]pyridin‐3‐ols 3 , which were dehydrated in the last step with SOCl₂ in the presence of pyridine to give the desired products. Similarly, thieno[2,3‐c]pyridine and thieno[3,2‐c]pyridine derivatives, 8 and 12 , respectively, can be prepared from aryl(3‐chloropyridin‐4‐yl)methanones 5 and aryl(4‐chloropyridin‐3‐yl)methanones 9 , respectively.     

New Approaches to the Synthesis of 4‐(2‐Aminophenyl)‐1,3‐dihydro‐2H‐imidazol‐2‐ones and 3‐Ureidoindoles and a Study of Their Interconversion

3‐Alkyl/aryl‐3‐ureido‐1H,3H‐quinoline‐2,4‐diones ( 2 ) and 3a‐alkyl/aryl‐9b‐hydroxy‐3,3a,5,9b‐tetrahydro‐1H‐imidazo[4,5‐c]quinoline‐2,4‐diones ( 3 ) react in boiling concentrated HCl to give 5‐alkyl/aryl‐4‐(2‐aminophenyl)‐1,3‐dihydro‐2H‐imidazol‐2‐ones ( 6 ). The same compounds were prepared by the same procedure from 2‐alkyl/aryl‐3‐ureido‐1H‐indoles ( 4 ), which were obtained from the reaction of 3‐alkyl/aryl‐3‐aminoquinoline‐2,4(1H,3H)‐diones ( 1 ) with 1,3‐diphenylurea or by the transformation of 3a‐alkyl/aryl‐9b‐hydroxy‐3,3a,5,9b‐tetrahydro‐1H‐imidazo[4,5‐c]quinoline‐2,4‐diones ( 3 ) and 5‐alkyl/aryl‐4‐(2‐aminophenyl)‐1,3‐dihydro‐2H‐imidazol‐2‐ones ( 6 ) in boiling AcOH. The latter were converted into 1,3‐bis[2‐(2‐oxo‐2,3‐dihydro‐1H‐imidazol‐4‐yl)phenyl]ureas ( 5 ) by treatment with triphosgene. All compounds were characterized by ¹H‐ and ¹³C‐NMR and IR spectroscopy, as well as atmospheric pressure chemical‐ionisation mass spectra.     

Synthesis of novel pyrido[3′,2′:5,6]thiopyrano[3,2‐b]indol‐5(6H)‐ones and 6H‐pyrido[3′,2′:5,6]thiopyrano[4,3‐b]quinolines,two new heterocyclic ring systems

The synthesis of new pyrido[3′,2′:5,6]thiopyrano[3,2‐b]indol‐5(6H)‐ones was accomplished by the Fischer‐indole cyclization of some 2,3‐dihydro‐3‐phenylhydrazonothiopyrano[2,3‐b]pyridin‐4(4H)‐ones, obtained from the 2,3‐dihydro‐3‐hydroxymethylenethiopyrano[2,3‐b]pyridin‐4(4H)‐one, by the Japp‐Klingemann reaction. 6H‐Pyrido[3′,2′:5,6]thiopyrano[4,3‐b]quinolines were obtained by reaction of 2,3‐dihydrothiopyrano‐[2,3‐b]pyridin‐4(4H)‐ones with o‐aminobenzaldehyde or 5‐substituted isatins. The preparation of some derivatives, functionalized with an alkylamino‐substituted side chain, is also described.     

Two‐Step Synthesis of 1,3‐Disubstituted 3,4‐Dihydro‐4‐thioxoquinazolin‐2(1H)‐ones from 1‐Bromo‐2‐fluorobenzenes

An efficient synthesis of 3‐alkyl‐3,4‐dihydro‐4‐thioxobenzoquinazolin‐2(1H)‐ones 3 has been accomplished in two steps and in satisfactory yields from 1‐bromo‐2‐fluorobenzenes 1 . Thus, the reaction of 1‐fluoro‐2‐lithiobenzenes, generated by the Br/Li exchange between 1 and BuLi, with alkyl isothiocyanates, gives N‐alkyl‐2‐fluorobenzothioamides 2 , which, in turn, react with a series of isocyanates in the presence of NaH to give the desired products 3 .     

Reaction of 3‐Hydroxyquinoline‐2,4‐diones with Isocyanates and Thermally Induced Transformation of the Reaction Products

3‐Hydroxyquinoline‐2,4‐diones 1 react with isocyanates to give novel 1,2,3,4‐tetrahydro‐2,4‐dioxoquinolin‐3‐yl (alkyl/aryl)carbamates 2 and/or 1,9b‐dihydro‐9b‐hydroxyoxazolo[5,4‐c]quinoline‐2,4(3aH,5H)‐diones 3 . Both of these compounds are converted, by boiling in cyclohexylbenzene solution in the presence of Ph₃P or 4‐(dimethylamino)pyridine, to give 3‐(acyloxy)‐1,3‐dihydro‐2H‐indol‐2‐ones 8 . All compounds were characterized by IR, and ¹H‐ and ¹³C‐NMR spectroscopy, as well as by EI mass spectrometry.     

Synthesis of 4‐halo‐2 (5H)‐furanones and their suzuki‐coupling reactions with organoboronic acids. A general route to 4‐aryl‐2 (5 H) ‐furanones

4‐Halo‐2(5H)‐furanones were prepared by the halolactonization of 2,3‐allenoic acids. The subsequent Suzuki coupling reaction of 4‐halo 2(5H)‐furanones with aryl boronic acids was carried out to produce 4‐aryl‐2(5H)‐furanones in excellent yields.     

Synthesis of 4‐Arylisocoumarins (=4‐Aryl‐1H‐2‐benzopyran‐1‐ones) through Acidic Hydrolysis of (Z)‐2‐(1‐Aryl‐2‐methoxyethenyl)benzaldehydes,Followed by Oxidation

4‐Arylisocoumarins (=4‐aryl‐1H‐2‐benzopyran‐1‐ones) 6 were prepared from 2‐(1‐aryl‐2‐methoxyethenyl)‐1‐bromobenzenes 1 . Successive treatment of these bromo styrenes with BuLi and 1‐formylpiperidine gave a mixture of (E)‐ and (Z)‐2‐(1‐aryl‐2‐methoxyethenyl)benzaldehydes 2 . Hydrolysis of (Z)‐isomers with conc. HBr, followed by pyridinium chlorochromate (PCC) oxidation of the resulting 1H‐2‐benzopyran‐1‐ol derivatives 4 (and 5 ), afforded the desired products.     

Synthesis of 2‐Substituted 3‐Alkylidene‐2,3‐dihydro‐1H‐isoindol‐1‐imines through Cyclization of [1‐(2‐Cyanophenyl)alkylidene]aminide Intermediates Generated from the Reaction of 2‐(1‐Azidoalkyl)benzonitriles with NaH

A convenient sequence for the preparation of 3‐alkylidene‐2,3‐dihydro‐1H‐isoindol‐1‐imine derivatives 6 has been developed. Thus, 2‐(1‐azidoalkyl)benzonitriles 2 , readily accessible from 2‐alkylbenzonitriles, are allowed to react with NaH in DMF at 0° to room temperature to generate [1‐(2‐cyanophenyl)alkylidene]aminide intermediates 3 , of which cyclization and the subsequent rearrangement, followed by alkylation with alkyl halides, affords 2‐substituted 1‐alkylidene‐2,3‐dihydro‐1H‐isoindol‐2‐imines 6 in generally moderate yields.     

Synthesis of 4‐Aryl‐1,7‐naphthyridine‐2(1H)‐thiones by the Electrocyclic Reaction of 4‐(1‐Arylalk‐1‐enyl)‐3‐isothiocyanatopyridines Generated in situ from the Corresponding Isocyanides

A convenient synthis for 4‐substituted and 3,4‐disubstituted 1,7‐naphthyridine‐2(1H)‐thiones 7 has been developed. The method is based on the electrocyclic reaction of 4‐(1‐arylalk‐1‐enyl)‐3‐isothiocyanatopyridines 6 , generated in situ by the treatment of the respective isocyanides 5 with S₈ in the presence of a catalytic amount of selenium. The isocyanides 5 can be easily prepared from commercially available pyridin‐3‐amine by conventional organic reactions.     

Ring Opening of 2‐(Benzylamino)‐2H‐1,4‐benzoxazin‐3(4H)‐ones and 2‐Bromo‐2H‐1,4‐benzoxazin‐3(4H)‐ones

Substituted 2‐(benzylamino)‐2H‐1,4‐benzoxazin‐3(4H)‐ones are unstable under alkaline and acidic conditions, undergoing opening of the benzoxazinone ring. 2‐Bromo‐2H‐1,4‐benzoxazin‐3(4H)‐ones show similar degradation under alkaline conditions, while replacement of Br at C(2) to give 2‐hydroxy‐2H‐1,4‐benzoxazin‐3(4H)‐ones was observed only under mild alkaline conditions. Mechanisms of ring opening and degradation to 2‐aminophenol derivatives are proposed.     

Efficient Synthesis of 1‐Arylquinoxalin‐2(1H)‐ones via Cyclocondensation of N‐Aryl‐Substituted 2‐Nitrosoanilines with Functionalized Alkyl Acetates

N‐Aryl‐substituted 2‐nitrosoanilines (=2‐nitrosobenzenamines) 1 , readily available by nucleophilic substitution of the ortho‐H‐atom in nitroarenes with arenamines, react with 2‐substituted acetic acid esters in the presence of a weak base giving 1‐arylquinoxalin‐2(1H)‐ones (Scheme 2). This cyclocondensation allows for the synthesis of compounds 2 – 4 , unsubstituted at C(3) or substituted by alkyl, aryl, ester, amide, and keto groups, in good to excellent yields (Tables 1–4).