Synthesis of 4‐hydroxyquinolin‐2(1H)‐one analogues and 2‐substituted quinolone derivatives

A versatile synthetic method for preparing 4‐hydroxyquinolone and 2‐substituted quinolone compounds from simple benzoic acid derivatives was demonstrated. The synthetic strategies involve the use of well known ethyl acetoacetate synthesis, malonic ester synthesis and reductive cyclization. The key intermediates were keto esters 4a‐e , which could be transformed to 4‐hydroxyquinolones 5a,b or 2‐substituted quinolone ethyl esters 6a‐c depending on the reaction conditions. 4‐Hydroxyquinolone analogues were prepared and investigated for N‐methyl‐D‐aspartate (NMDA) activity in vitro. Among these derivatives, 6,7‐difluoro‐3‐nitro‐4‐hydroxyquinolin‐2(1H)‐one ( 9 ) exhibited moderate activity.     

An efficient synthesis of 1‐H‐pyrazole‐4‐carboxylic acid esters with vilsmeier reagent under neat conditions

A convenient, solvent‐free Vilsmeier reagent is experimented under neat condition (both thermal and microwave conditions). An efficient method for the synthesis of various substituted 1H‐pyrazole‐4‐carboxylic acid esters is reported.     

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).     

Efficient Synthesis of 1‐Aryl‐4‐[(ethoxycarbonyl)oxy]‐1H‐pyrazole‐3‐carboxylates

Two‐step synthesis of N‐aryl 4‐[(ethoxycarbonyl) oxy]‐1H‐pyrazole‐3‐carboxylates is achieved starting from the commercially available ethyl 4‐chloroacetoacetate and aromatic amines. Azo coupling followed by cyclization with ethyl chloroformate–DMAP pair resulted in the formation of new 4‐oxy‐1H‐pyrazole derivatives in high yields.     

Synthesis of 2‐Coumarinyl and Spiroindolyl‐5‐Phenyl‐1,3,4‐Oxadiazoles

The 2H‐1‐benzo/naphthopyran‐2‐one‐4‐yl (un)substituted phenyl‐1,3,4‐oxadiazoles has been synthesized by the oxidative cyclization of benzoic acid hydrazides formed in situ by the condensation of the respective 2H‐1‐benzo/naphthopyran‐2‐one‐4‐carboxaldehyde and (un)substituted monobenzoyl hydrazide in moderate yields. Also, spiro[indoline‐thiozolidine]‐2,4′‐diones has been syhthesized in a similar way from 3‐phenyl‐spiro[3H‐indoline‐3,2′‐thiozolidine]‐2,4′‐(1 H)dione monohydrazide and (un)substituted benzaldehydes.     

Four (E,Z,E)‐1‐(4‐alkoxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐trienes

The crystal structures of the four E,Z,E isomers of 1‐(4‐alk­oxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐triene, namely (E,Z,E)‐1‐(4‐methoxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐triene, C₁₉H₁₇NO₃, (E,Z,E)‐1‐(4‐ethoxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐triene, C₂₀H₁₉NO₃, (E,Z,E)‐1‐(4‐nitro­phen­yl)‐6‐(4‐n‐propoxyphen­yl)hexa‐1,3,5‐triene, C₂₁H₂₁NO₃, and (E,Z,E)‐1‐(4‐n‐butoxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐triene, C₂₂H₂₃NO₃, have been determined. Inter­molecular N⋯O dipole inter­actions between the nitro groups are observed for the meth­oxy derivative, while for the eth­oxy derivative, two adjacent mol­ecules are linked at both ends through N⋯O dipole–dipole inter­actions between the N atom of the nitro group and the O atom of the eth­oxy group to form a supra­molecular ring‐like structure. In the crystal structures of the n‐prop­oxy and n‐but­oxy derivatives, the shortest inter­molecular distances are those between the two O atoms of the alk­oxy groups. Thus, the nearest two mol­ecules form an S‐shaped supra­molecular dimer in these crystal structures.     

Synthesis of novel 6,7‐dihydro‐5H‐pyrimido[4,5‐e][1,4]diazepin‐8(9H)‐ones

A new method was developed for the synthesis of 6,7‐dihydro‐5H‐pyrimido[4,5‐e][1,4]diazepin‐8(9H)‐one derivatives. The key to construct the pyrimido[4,5‐e][1,4]diazepine core is the intramolecular amidation of N‐((4‐amino‐6‐chloropyrimidin‐5‐yl)methyl)‐substituted amino acid esters. This methodology was validated through the preparation of 13 representative 6,7‐dihydro‐5H‐pyrimido[4,5‐e][1,4]diazepin‐8(9H)‐ones in moderate to good yields. J. Heterocyclic Chem., (2011).     

Heterocyclic compounds from 4h‐3,1‐benzoxazin‐4‐one derivatives as anticancer agent

Behaviour of 2‐(4‐oxo‐4H‐benzo[d][l,3]oxazin‐2‐yl)‐benzoic acid (1) towards nitrogen nucleophiles namely, hydrazine hydrate, in different solvents, ammonium acetate, and o‐phenylenediamine has been investigated to give aminoquinazolin‐4‐one, benzotriazepinone, spiro‐type compound, and nitrogen bridgehead compounds 3‐5 , respectively. Also, reactivity of the aminoquinazolin‐4‐one 2 towards carbon elec‐trophiles such as ethyl acetoacetate, ethyl phenylacetate, ethyl chloroacetate, and aromatic aldehydes has been discussed. Reaction of Schiff s base 8 with sulfur nucleophiles namely o‐aminothiophenol and/or thio‐glycolic acid afforded Michael type adducts. Structural assignments, of products 1‐24 have been confirmed by elemental analysis and spectral data (¹H‐ and ¹³C ‐NMR and MS fragmentation). The bioassay indicates that some of the target compounds obtained have good selective anticancer activity.     

Radical 4‐exo Cyclizations onto O‐Alkyloxime Acceptors: Towards the Synthesis of Penicillin‐Containing Antibiotics

The 4‐exo cyclizations of two types of carbamoyl radicals onto O‐alkyloxime acceptor groups were studied as potential routes to 3‐amino‐substituted azetidinones and hence to penicillins. A general synthetic route to ‘benzaldehyde oxime oxalate amides’ (= 2‐[(benzylideneamino)oxy]‐2‐oxoacetamides; see, e.g., 10c ) of 2‐{[(benzyloxy)imino]methyl}‐substituted thiazolidine‐4‐carboxylic acid methyl esters 9 was developed (Scheme 3). It was shown by EPR spectroscopy that these compounds underwent sensitized photodissociation to the corresponding carbamoyl radicals but that these did not ring close. An analogous open‐chain precursor, benzaldehyde O‐(benzylaminoacetaldehyde‐O‐benzyloxalyl)oxime, 15 , lacking the 5‐membered thiazolidine ring, was shown by EPR spectroscopy to release the corresponding carbamoyl radical (Scheme 4). The latter underwent 4‐exo cyclization onto its C?NOBn bond in non‐H‐atom donor solvents. The rate constant for this cyclization was determined by the steady‐state EPR method. Spectroscopic evidence indicated that the reverse ring‐opening process was slower than cyclization.     

Disappearance of intramolecular stacking due to one‐atom movement or increment of a `propyl­ene linker' in pyrazolo­[3,4‐d]­pyrimidine‐based ­flexible models

In the crystal structures of 4,6‐di­methyl­thio‐1‐[3‐(4,6‐di­methyl­thio‐2H‐pyra­zolo­[3,4‐d]­py­rimi­din‐2‐yl)­propyl]‐1H‐py­ra­­zolo­[3,4‐d]­py­rimi­dine, C₁₇H₂₀N₈S₄, and 1‐[4‐(4‐meth­oxy‐6‐methyl­thio‐1H‐pyra­zolo­[3,4‐d]py­rimi­din‐1‐yl)­butyl]‐5‐meth­yl‐6‐methyl­thio‐4,5‐di­hydro‐1H‐pyra­zolo­[3,4‐d]py­rimi­din‐4‐one, C₁₈H₂₂N₈O₂S₂, only intermolecular stacking due to aromatic π–π interactions between pyrazolo­[3,4‐d]­pyrimidinerings is present.     

The α‐ and β‐epoxides of 3β‐acet­oxy‐5α‐lanost‐9(11)‐en‐7‐one

The structures of 3β‐acet­oxy‐9α,11α‐ep­oxy‐5α‐lanost‐9(11)‐en‐7‐one and 3β‐acet­oxy‐9β,11β‐ep­oxy‐5α‐lanost‐9(11)‐en‐7‐one, C₃₂H₅₂O₄, differ in their respective substituted cyclo­hexa­none rings but adopt similar conformations in the other three rings. In both of the crystal structures, weak inter­molecular C—H⋯O inter­actions are present.     

An easy route to 2‐substituted‐2,3‐dihydro‐5(7)H‐oxazolo[3,2‐a]pyrimidin‐5‐ones and 7‐ones starting from the corresponding 2‐amino‐2‐oxazolines

The isomeric 2‐substituted‐7(5)‐methyl‐2,3‐dihydro‐5(7)H‐oxazolo[3,2‐a]pyrimidin‐5‐ones 3a‐b and 7‐ones 2a‐b,7a were synthesized by cyclocondensation from the 5‐substituted‐2‐amino‐2‐oxazolines 1a‐b with biselectrophiles. In boiling ethanol, the reaction of 1a‐b with acetylenic esters led to a mixture of 2a‐b,7a with a small amount of (E)‐2‐N‐(2‐ethoxycarbonylethylene)‐5‐substituted‐2‐iminooxazolines 5a‐b . The ring annulation between 1a‐b and diketene gave the 2‐substituted‐7‐hydroxy‐7‐methyl‐2,3,6,7‐tetrahydro‐5H‐oxazolo[3,2‐ a ]pyrimidin‐5‐ones 4a‐b which can be easily dehydrated to provide the 2‐substituted‐7‐methyl‐2,3‐dihydro‐5H‐oxazolo[3,2‐a]pyrimidin‐5‐ones 3a‐b .     

(E,E)‐2,5‐Diprop­oxy‐1,4‐bis­[2‐(2,4,6‐trimethoxy­phen­yl)ethen­yl]benzene

The title compound, C₃₀H₃₄O₈, crystallizes in the space group P with one‐half of a mol­ecule in the asymmetric unit. A three‐dimensional network is generated by OCH₃⋯π and CH⋯π inter­actions. The conformation of the C—C bond exocyclic to the central benzene ring is different from that of every other known derivative. A comparison of the geometry of the title mol­ecule and of its solid‐state structure with other 2,4,6‐trimeth­oxy‐substituted PPV [i.e. poly(p‐phenylenevinylene)] oligomers, in particular the isoprop­oxy‐substituted compound, is provided.     

Reactivity study on morpholine‐1‐carbothioic acid (2‐phenyl‐3H‐quinazolin‐4‐ylidene) amide

Regioselective reactions of morpholine‐1‐carbothioic acid (2‐phenyl‐3H‐quinazolin‐4‐ylidene) amide ( 1 ) with electrophiles and nucleophiles were studied. The compound ( 1 ) reacts with alkyl halides in basic medium to afford S‐substituted isothiourea derivatives, with amines to give 1,1‐disubstituted‐3‐(2‐phenyl‐3H‐quinazolin‐4‐ylidene) thioureas and l‐substituted‐3‐(2‐phenyl‐quinazolin‐4‐yl) thioureas via transami‐nation reaction. The reaction of ( 1 ) with amines in the presence of H₂O₂ provided N⁴‐disubstituted‐N'⁴‐(2‐phenylquinazolin‐4‐yl)morpholin‐4‐carboximidamide via oxidative desulfurization. Estimation of reactivity sites on ( 1 ) was supported using the ab initio (HF/6‐31G**) quantum chemistry calculations. The ir, ¹H nmr, ¹³C nmr, mass spectroscopy and x‐ray identified the isolated products.     

An efficient and regiospecific preparation of trifluoromethyl substituted 4‐( 1H‐pyrazol‐1 ‐yl)‐7‐chloroquinolines

A new series of 4‐[3‐alkyl(aryl)(heteroaryl)‐5‐hydroxy‐5‐trifluoromethyl‐4,5‐dihydro‐1H‐pyrazol‐1‐yl]‐7‐chloroquinolines, where [alkyl = CH₃; aryl = C₆H₅, 4‐CH₃C₆H₄, 4‐FC₆H₄, 4‐ClC₆H₄, 4‐BrC₆H₄, 4‐CH₃OCgH₄, 4‐NO₂CgH₄, 4‐biphenyl, 1‐naphthyl; heteroaryl = 2‐furyl and 2‐thienyl] has been regiospecifi‐caly obtained from the reaction of 7‐chloro‐4‐hydrazinoquinoline with 4‐substituted‐l,1,1‐trifluoro‐4‐methoxybut‐3‐en‐2‐ones in 61 ‐ 96 % yield. Subsequently, dehydration reaction of 4,5‐dihydropyra‐zolylquinolines under acid conditions furnished a new series of 4‐(3‐substituted‐5‐trifluoromethyl‐1H‐pyra‐zol‐1‐yl)‐7‐chloroquinolines in 73 ‐ 96 % yield.     

A new efficient synthesis of 3‐(hydroxymethyl)‐4H‐chromen‐4‐ones

An efficient and versatile synthesis of variously substituted 3‐(hydroxymethyl)‐4H‐chromen‐4‐ones is reported. The compounds are prepared by hydroxymethylation of the precursor 2‐hydroxy‐4‐chromanones followed by acid dehydration.     

Synthesis and characterization of some novel 2‐{2‐[1‐(3‐substituted‐phenyl)‐1H‐1,2,3‐triazol‐4‐yl‐] ethyl}‐1‐substituted‐1H‐benzo [d] imidazole derivatives

Synthesis of some novel 2‐{2‐[1‐(3‐substitutedphenyl)‐1H‐1,2, 3‐triazol‐4‐yl‐]ethyl)‐1H‐benzo[d]‐imidazole derivatives, by the condensation of o‐phenylenediamine with 3‐(1‐(3‐substituted‐phenyl)‐1H‐1,2,3‐triazol‐4‐yl) propanoic acid and then subsequent reactions with different substituted alkyl halides as electrophiles are mentioned. The synthesized compounds were characterized by ¹H NMR, EI‐MS and IR spectroscopic techniques.     

Synthesis and Functionalization of 8‐Methyl‐2h‐pyrimido [2,1‐c][1,2,4]triazine‐3,6(1h,4h)‐dione

6‐Methyl‐2‐methylthio‐4‐oxopyrimidin‐3(4H)‐yl)acetohydrazide on heating in benzylamine undergo cyclization to 8‐methyl‐2H‐pyrimido[2,1‐c][1,2,4]triazine‐3,6(1H, 4H)‐dione, which under treatment with bromine in glacial acetic acid was converted to 7‐bromo substituted derivative and at reflux with Lawesson's reagent yielded 3‐thioxo compound. The latter reacted with primary and secondary amines to give 3‐amino substituted pyrimidotriazines and on alkylation—the corresponding S‐alkyl derivatives.     

Formation of 1,3‐Thiazol‐5(4H)‐imines and 1,3‐Oxazol‐5(4H)‐imines in Aib‐Containing Thiopeptides

When tripeptides of type Axx^t‐Aib‐Axx‐OH were coupled with amino acid methyl esters by means of commonly used coupling reagents, the formation of 1,3‐thiazol‐5(4H)‐imines and 1,3‐oxazol‐5(4H)‐imines was observed. With the aim of understanding which structure elements are required for this reaction, several model peptides have been prepared according to our recently described methodology, a modification of the ‘azirine/oxazolone method', followed by selective isomerization of the peptide thioamides. In addition, attempts to prepare peptides that contain more than one C=S group by the same methodology also led to the formation of 1,3‐thiazol‐5(4H)‐imine‐containing derivatives. An additional C=S group can be introduced into the peptide, when the 1,3‐thiazol‐5(4H)‐imines were treated with H₂S, although mixtures of epimers were obtained. The structures of an endothiohexapeptide, two 1,3‐thiazol‐5(4H)‐ones, and two peptides containing a 1,3‐thiazol‐5(4H)‐imine moiety have been established by X‐ray crystal‐structure analysis.     

Synthesis and Antimicrobial Activity of N‐Aryl‐4‐(cyano/alkoxycarbonyl)‐5‐(pyridin‐3‐yl)‐1H/3H‐1,2,3‐triazole Derivatives

A convenient synthesis of a new series of N‐aryl‐5‐(pyridin‐3‐yl)‐1H/3H‐1,2,3‐triazole‐4‐carbonitriles and alkyl N‐aryl‐5‐(pyridin‐3‐yl)‐1H/3H‐1,2,3‐triazole‐4‐carboxylic acid esters is reported. The newly synthesized 5‐(pyridin‐3‐yl)‐1,2,3‐triazole derivatives are evaluated for their antibacterial and antifungal activity. Some of these triazole derivatives have exhibited moderate antimicrobial activity.