New Methods for the Synthesis of 3‐Amino‐6,7‐Dihydro‐5H‐Cyclopenta[c]Pyridine‐4‐Carbonitriles and Cyclopenta[d]Pyrazolo[3,4‐b]Pyridines via a Smiles‐type Rearrangement

By reaction with sodium ethoxide and as a function of their structures, 2‐[(1‐alkyl(aryl)‐4‐cyano‐6,7‐dihydro‐5H‐cyclopenta[c ]pyridin‐3‐yl)oxy]acetamides 11 gave 1‐amino‐5‐alkyl(aryl)‐7,8‐dihydro‐6H‐cyclopenta[d ]furo[2,3‐b ]pyridine‐2‐carboxamides 10 and/or 1‐alkyl(aryl)‐3‐amino‐6,7‐dihydro‐5H‐cyclopenta[c ]pyridine‐4‐carbonitriles 12 .     

Microwave‐assisted Synthesis of 6‐{(5‐Aryl‐1,3,4‐oxadiazol‐2‐yl)methyl}‐6H‐indolo[2,3‐b]quinoxalines

An efficient and convenient synthesis of a new series of 2‐{(6H‐indolo[2,3‐b]quinoxalin‐6‐yl)methyl}‐5‐aryl‐1,3,4‐oxadiazoles from readily available 1,2‐diaminobenzene and isatins under microwave irradiation conditions was disclosed. The 6‐{(5‐aryl‐1,3,4‐oxadiazol‐2‐yl)methyl}‐6H‐indolo[2,3‐b]quinoxalines were also prepared by the thermal cyclo‐condensation reaction of 2‐(6H‐indolo[2,3‐b]quinoxalin‐6‐yl)acetohydrazides with carboxylic acids in refluxing POCl₃. The microwave‐assisted synthesis was rapid and resulted in higher yield of the products at lower operating temperature with reduced waste generation in comparison with the thermal reaction protocol.     

Strategy to Construct Stair‐Shaped Partially Reduced Naphtho[1,2‐b]pyrano[2,3‐d]oxepines and Dinaphtho[1,2‐b,d]oxepines

A concise and efficient base‐induced synthesis of stair‐shaped, 4‐methylthio‐2‐oxo‐5,6‐dihydro‐2H‐naphtho[1,2‐b]pyran[2,3‐d]oxepine‐3‐carbonitriles ( 3 ) has been delineated by the reaction of 3,4‐dihydronaphtho[1,2‐b]oxepin‐5(2H)‐one ( 1 ) and methyl 2‐cyano‐3,3‐dimethylthioacrylate in DMSO using powdered KOH as a base at room temperature. Amination of 3 has been achieved by reaction with secondary amine in ethanol at reflux temperature to yield 4‐sec‐amino‐2‐oxo‐5,6‐dihydro‐2H‐naphtho[1,2‐b]pyran[2,3‐d]oxepine‐3‐carbonitriles ( 4 ). Reaction of 3 with aryl methyl ketone ( 5 ) in DMSO at room temperature using powdered KOH as a base produced stair‐shaped 5‐aryl‐7,8‐dihydro‐1,4‐dioxa‐2,3‐dioxodinaphtho[1,2‐b,d]oxepine ( 6 ) in good yields. However, reaction of 6‐aryl‐2H‐pyran‐2‐one‐3‐carbonitrile ( 8 ) with 3,4‐dihydronaphtho[1,2‐b]oxepin‐5(2H)‐one ( 1 ) did not give similar product, but in lieu 4‐aryl‐5,6‐dihydronaphtho[1,2‐b]oxepino[4,5‐b]pyran‐2‐ylidene)acetonitrile ( 9 ) was isolated and characterized.     

Synthesis of thiazole,oxazole and heterocyclic ring‐substituted 1,2‐dioxanes

The reactions of 4‐bromoacetyl‐3‐methoxy‐3‐methyl‐6,6‐diphenyl‐1,2‐dioxane with thioureas or thioamides gave 3‐methoxy‐3‐methyl‐6,6‐diphenyl‐4‐(4‐thiazolyl)‐1,2‐dioxanes in 63–90% yields. The similar reaction of 4‐bromoacetyl‐3‐methoxy‐3‐methyl‐6,6‐diphenyl‐1,2‐dioxane with acetamide gave 3‐methoxy‐3‐methyl‐4‐(2‐methyl‐4‐oxazolyl)‐6,6‐diphenyl‐1,2‐dioxane in 39% yields. The reactions of 4‐bromoacetyl‐3‐methoxy‐3‐methyl‐6,6‐diphenyl‐1,2‐dioxane with 3‐alkyl‐4‐amino‐5‐mercaptot[1,2,4]triazoles yielded 3‐methoxy‐3‐methyl‐6,6‐diphenyl‐4‐[3‐(5‐alkyl[1,2,4]triazolo[3,4‐b]‐2,3‐dihydro‐6H‐[1,3,4]thiadiazinyl)]‐1,2‐dioxanes in moderate yields (43–46%).     

Green Synthesis of 6‐Aryl‐5,6‐dihydrobenzo[4,5]imidazo[1,2‐c]quinazoline Derivatives in Ionic Liquid under Catalyst‐free Conditions

Using ionic liquids as green media, a series of 6‐arylbenzo[4,5]imidazo[1,2‐c]quinazoline derivatives is synthesized via a reaction of 2‐(1H‐benzo[d]imidazol‐2‐yl)aniline and benzaldehydes in the air. While the intermediate products of 6‐aryl‐5,6‐dihydrobenzo[4,5]imidazo[1,2‐c]quinazolines were obtained in high yields at the same conditions under nitrogen protection.     

Three‐Component One‐Pot Synthesis of 4‐Aryl‐2,3‐dihydropyrimido[1,2‐a]benzimidazol‐2‐ones Catalyzed by l‐Proline

An efficient chemoselective synthesis of 4‐aryl‐2,3‐dihydropyrimido[1,2‐a]benzimidazol‐2‐one derivatives from three‐component reactions of 2‐aminobenzimidazole, Meldrum's acid, and aldehydes via [3+3] atom combination is described. The reaction occurs in different conditions such as in DMF as solvent at reflux and in the presence of l ‐proline as base catalyst.     

Facile one‐pot synthesis of a series of 7‐aryl‐8H‐benzo[h]indeno[1,2‐b]quinoline‐8‐one derivatives catalyzed by cellulose‐based magnetic nanocomposite

A sulfonated magnetic cellulose‐based nanocomposite was applied as an efficient, inexpensive and green catalyst for the one‐pot three‐component synthesis of 7‐aryl‐8H ‐benzo[h ]indeno[1,2‐b ]quinoline‐8‐ones starting from 1,3‐indanedione, aromatic aldehydes and 1‐naphthylamine under solvent‐free conditions in high yields (79–98%) within short reaction times (2–5 min). The nanobiostructure catalyst can be easily separated from the reaction mixture by using an external magnet and reused several times.     

Reactions of 4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidines with α,β‐unsaturated carbonyl compounds

The reaction of 5,7‐diphenyl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidine ( 1 ) with α,β‐unsaturated carbonyl compounds 2a‐f led to the formation of the alkylated heterocycles 3a‐f (Figure 1). However, the reaction of 5‐methyl‐7‐phenyl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidine ( 5 ) with 2a‐c yielded under the same conditions the triazolo[5,1‐b]quinazolines 6a‐c (Figure 3). In this case, the alkylation is followed by a cyclocondensation. The structure elucidation of the products is based on ir, ms, ¹H and ¹³C nmr measurements and on an X‐ray diffraction study.     

Isocyanide‐Based Three‐Component Synthesis of Highly Substituted 1,6‐Dihydro‐6,6‐dimethylpyrazine‐2,3‐dicarbonitrile, 3,4‐Dihydrobenzo[g]quinoxalin‐2‐amine,and 3,4‐Dihydro‐3,3‐dimethyl‐quinoxalin‐2‐amine Derivatives

A novel and efficient isocyanide‐based multicomponent reaction between alkyl or aryl isocyanides 1 , 2,3‐diaminomaleonitrile ( 2 ), naphthalene‐2,3‐diamines ( 6 ) or benzene‐1,2‐diamine ( 9 ), and 3‐oxopentanedioic acid ( 3 ) or Meldrum's acid ( 4 ) or ketones 7 was developed for the ecologic synthesis, at room temperature under mild conditions, of 1,6‐dihydropyrazine‐2,3‐dicarbonitriles 5a – 5f in H₂O without using any catalyst, and of 3,4‐dihydrobenzo[g]quinoxalin‐2‐amine and 3,4‐dihydro‐3,3‐dimethyl‐quinoxalin‐2‐amine derivatives 8a – 8g and 10a – 10e , respectively, in the presence of a catalytic amount of p‐toluenesulfonic acid (TsOH) in EtOH, in good to excellent yields (Scheme 1).     

One‐Pot Three‐Component Synthesis of Pyrido[2,3‐c]carbazole Derivatives in EtOH under Catalyst‐Free Conditions

A three‐component reaction of aromatic aldehydes, 9‐ethyl‐9H‐carbazol‐3‐amine, and cyclopentane‐1,3‐dione or tetronic acid was carried out in EtOH at refluxing and gave two series of 2,3,7,12‐tetrahydrocyclopenta[5,6]pyrido[2,3‐c ]carbazol‐1(4H )‐one and 3,4,7,12‐tetrahydro‐1H‐furo[3′,4′:5,6]pyrido[2,3‐c ]carbazol‐1‐one derivatives, respectively. This procedure approach to pyrido[2,3‐c ]carbazoles has the advantages of milder reaction conditions, one‐pot, catalyst free, and high yields.     

The psuedo‐michael reaction of 2‐aminoimidazolines 2. Part 1. Synthesis and structure assignment of isomeric 5(1H)‐Oxo and 7(1H)‐Oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates

The pseudo‐Michael reaction of 1‐aryl‐2‐aminoimidazolines‐2 with diethyl ethoxymethylenemalonate (DEEM) was investigated. Extensive structural studies were performed to confirm the reaction course. For derivatives with N1 aromatic substituents, it was found that the reaction course was temperature dependent. When the reaction temperature was held at ?10 °C only the formation of 1‐aryl‐7(1H)‐oxo‐2,3‐dihydroimi‐dazo[1,2‐a]pyrimidine‐6‐carboxylates ( 4 ) was observed in contrast to earlier suggestions. Under the room temperature conditions, the same reaction yielded mixtures, with varying ratio, of isomeric 1‐aryl‐7(1H)‐oxo‐ ( 4a‐4f ) and 1‐aryl‐5(1H)‐oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates ( 5a‐5f ). The molecular structure of selected isomers, 4b and 5c , was confirmed by X‐ray crystallography. Frontal chro‐matography with delivery from the edge was applied for the separation of the isomeric esters. The isomer ratio of the reaction products depended on the character of the substituents on the phenyl ring. The 1‐aryl‐7(1H)‐oxo‐carboxylates ( 4a‐4f ) were preferably when the phenyl ring contained H, 4‐CH₃, 4‐OCH₃ and 3,4‐Cl₂ substituents. Chloro substitution at either position 3 or 4 in the phenyl ring favored the formation of isomers 5a‐5f . The isomer ratios were confirmed both by ¹H NMR and chromatography. The reaction of the respective hydrobromides of 1‐aryl‐2‐aminoimidazoline‐2 with DEEM, in the presence of triethylamine, gave selectively 5(1H)‐oxo‐esters ( 5a‐5f ).     

Ring Opening and Recyclization Reactions with Chromone‐3‐carbonitrile

Chemical transformations of chromone‐3‐carbonitrile ( 1 ) with some substituted hydrazines, namely, thiosemicarbazide, S‐methyl/benzyldithiocarbazate, 7‐chloro‐4‐hydrazinoquinoline, and 3‐hydrazino‐5,6‐diphenyl‐1,2,4‐triazine, led to substituted pyrazoles 2 , 5 – 8 . Ring opening of carbonitrile 1 followed by recyclization with 3‐amino‐1,2,4‐triazole and 2‐aminobenzimidazole gave triazolo[1,5‐a]pyrimidine 9 and pyrimido[1,2‐a]benzimidazole 10 , respectively. Treatment of carbonitrile 1 with some heterocyclic amines produced 2‐amino‐3‐substituted‐chromones 11 and 12 . The novel 3‐hydroxychromeno[4,3‐b]pyrazolo[4,3‐e]pyridin‐5(1H)‐one ( 13 ) was efficiently synthesized from the ring conversion of carbonitrile 1 with cyanoacetohydrazide. A mixture of chromeno[2,3‐b]naphthyridine 14 and chromeno[4,3‐b]pyridine 15 was obtained from base catalyzed transformation of carbonitrile 1 with malononitrile dimer. A diversity of novel annulated chromeno[2,3‐b]pyridines 16 – 22 was also synthesized. Chromeno[2,3‐b]pyrrole‐2‐carboxylate 23 was obtained from the reaction of carbonitrile 1 with ethyl chloroacetate. Structures of the new synthesized products were deduced on the basis of their analytical and spectral data.     

First synthesis of novel pentaheterocyclic ring system of 1,2,4‐triazolo[2″,3″:6′,1′]pyrimido[4′,5′:2,3]pyrido[1,2‐a]benzimidazole

Reaction of 1‐amino‐3‐arylpyrido[1,2‐a]benzimidazole‐2,4‐dicarbonitrile (1) with dimethylformamide‐dimethylacetal (DMF‐DMA) gave 1 ‐[N,N‐(dimethylaminomethylene)amino]‐3‐arylpyrido[1,2‐a]benzimidazole‐2,4‐dicarbonitrile (2). Compounds (1) reacted with triethylorthoformate yielding 1‐[N‐(ethoxymethylene)amino]‐3‐arylpyrido[1,2‐a]benzimidazole‐2,4‐dicarbonitrile (3). 3‐Amino‐4‐imino‐5‐aryl‐6‐cyanopyrimido[5′,4′:5,6]pyrido[1,2‐α] benzimidazole (4) was synthesized via condensation of either (2) or (3) with hydrazine hydrate. Reactions of (4) with acetic anhydride, ethyl chloroformate or aryl isothiocyanate yielded the respective derivative of the new ring system namely 1,2,4‐triazolo[2″,3″:6′,1′]pyrimido[4′,5′:2,3]pyrido[1,2‐a]benzimidazole (5–7).     

Synthesis of novel pyrido[3′,2′:4,5]thieno[3,2‐d]pyrimidines,pyrido[3″,2″:4′,5′]thieno[3′,2′:4,5]pyrimido[l,6‐a]benzimidazoles and related fused systems

3‐Amino‐4‐aryl‐5‐ethoxycarbonyl‐6‐methylthieno[2,3‐b]pyridine‐2‐carboxamides 3a‐c were prepared from ethyl 4‐aryl‐3‐cyano‐6‐methyl‐2‐thioxo‐1,2‐dihydropyridine‐5‐carbonylates 1a‐c and reacted with some carbonyl compounds to give tetrahydropyridothienopyrimidine derivatives 6a‐c, 7a‐c and 8a‐c , respectively. Treatment of compound 3c with chloroacetyl chloride led to the formation of a next key compound, ethyl 2‐chloromethyl‐4‐oxo‐3,4‐dihydropyrido[3′,2′:4,5]thieno[3,2‐d]pyrimidine‐8‐carboxylate 9 . Also, 3‐amino‐2‐benzimidazolylthieno[2,3‐b]pyridine‐5‐carboxylate 5 and 2‐(3′‐aminothieno [2,3‐b]pyridin‐2′‐yl)‐4‐oxo‐3,4‐dihydropyrido[3′,2′:4,5]thieno[3,2‐d]pyrimidine‐8‐carboxylate 17 were prepared from 1c. The compounds 5, 9 and 17 were used as good synthons for other pyridothienopyrimidines and pyridothienopyrimidobenzimidazoles as well as for related fused polyheterocyclic systems.     

Syntheses of thiopyrone and pyrone derivatives by photocyclization reaction of 3‐aryl‐2‐( Benzothien‐3‐yl)propenoic acids

Naphtho[1,2‐b][1]benzothiophene‐6‐carboxylic acids, 6H‐benzo[b]naphtho[2,3‐d]thiopyran‐6‐ones and 6H‐benzo[b]naphtho[2,3‐d]pyran‐6‐ones were synthesized in one step by the photocyclization reaction of 3‐aryl‐2‐([1]benzothien‐3‐yl)propenoic acids. The photocyclization reaction did not occur when the 3‐aryl group contained the electron‐withdrawing nitro group. The assignment of the ¹H and ¹³C nmr spectra of 6H‐benzo[b]naphtho[2,3‐d]thiopyran‐6‐one and 6H‐benzo[b]naphtho[2,3‐d]pyran‐6‐one by two‐dimensional nmr methods is described. The difference between the chemical shift values of H12 for these two compounds is attributed to different molecular geometries.     

Reactions of 3‐methylamino‐5‐phenylthiophene with α,β‐unsaturated esters and α,β‐unsaturated nitriles

Treatment of 3‐methylamino‐5‐phenylthiophene with α,β‐unsaturated esters, i.e., methyl acrylate, (E)‐methyl crotonate, diethyl fumarate, diethyl maleate and ethyl propiolate, in tetrahydrofuran for several days at reflux gave 1‐methyl‐3,4‐dihydrothieno[2,3‐e]pyridin‐2‐ones 4 and/or 1‐methylthieno[2,3‐e]pyridin‐2‐ones 5 , depending on the structure of the esters. On the other hand, the same reactions with α,β‐unsaturated nitriles such as acrylonitrile and tetracyanoethene, gave the corresponding thiophenes 7 and 10 bearing 2‐cyanoethyl and 1,2,2‐tricyanoethenyl groups at C‐2, respectively. The reaction with (Z)‐1,2‐dicyanoethene under the same conditions produced the corresponding thiophene 9 bearing the 1,2‐dicyanoethenyl group and 1,2‐dicyano‐5‐methylaminobiphenyl.     

Polycyclic N‐Heterocyclic Compounds,Part 69: Synthesis of 5‐amino‐1,2‐dihydro[1]benzofuro[3,2‐d]furo[2,3‐b]pyridines and their transformations to related compounds

Reaction of 3‐(3‐cyanopropoxy)[1]benzofuran‐2‐carbonitriles with potassium tert‐butoxide gave 5‐amino‐1,2‐dihydro[1]benzofuro[3,2‐d]furo[2,3‐b]pyridines and 5‐amino‐2,3‐dihydro[1]benzofuro[3,2‐b]oxepin‐4‐carbonitriles as new ring systems. Reactions of the 5‐chloro derivative, obtained from 5‐amino‐1,2‐dihydro[1]benzofuro[3,2‐d]furo[2,3‐b]pyridine, produced a dihydrofuran ring‐opened compound and 5‐substituted compounds. J. Heterocyclic Chem.,(2011).     

Syntheses of New Unsymmetrical 2,5‐Disubstituted‐1,3,4‐oxadiazoles and 1,2,4‐Triazolo[3,4‐b]‐1,3,4‐thiadiazoles Bearing Thieno[2,3‐c]pyrazolo Moiety

New series of (thieno[2,3‐c]pyrazolo‐5‐yl)‐[1,2,4]triazolo[3,4‐b][1,3,4]thiadiazoles 10a , 10b , 10c and (thieno[2,3‐c]pyrazol‐5‐yl)‐1,3,4‐oxadiazol‐3(2H)‐yl)ethanones 6a , 6b , 6c has been synthesized from thieno[2,3‐c]pyrazole‐5‐carbohydrazide 3 by multistep reaction sequence. (5‐Aryl‐1,3,4‐oxadiazol‐2‐yl)‐1H‐thieno[2,3‐c]pyrazoles 4a , 4b , 4c were also synthesized from thieno[2,3‐c]pyrazole‐5‐carbohydrazide 3 by cyclization with various aromatic carboxylic acids. The hydrazide 3 was obtained by reaction of thieno[2,3‐c]pyrazole‐5‐carboxylate 2 with hydrazine hydrate in good yield, and compound 2 was obtained by the reaction of 5‐chloro‐3‐methyl‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde 1 and 2‐ethyl thioglycolate in presence of sodium alcoholate in good yield.     

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.     

Polycyclic N‐Heterocyclic Compounds. Part 81: Synthesis and Evaluation of Pentacyclic 1,2,4,5‐Tetrahydro[1]benzothieno[2′,3′:6,7]thiepino[4,5‐e]imidazo[1,2‐c]pyrimidine and Related Compounds as Potential Antiplatelet Aggregators

Dehydrative ring closure reactions were carried out on fused 4‐(2‐hydroxyethylamino) (or 2‐hydroxyethoxy or 2‐hydroxyethylthio)pyrimidines ( 2a , 2b , 2c ) to give fused 2,3‐dihydroimidazo[1,2‐c] (or 2,3‐dihydrooxazolo[3,2‐c] or 2,3‐dihydrothiazolo[3,2‐c])pyrimidines. This reaction produced the pentacyclic 1,2,4,5‐tetrahydro[1]benzothieno[2′,3′:6,7]thiepino[4,5‐e]imidazo[1,2‐c]pyrimidine ( 3a ) and 1,2,4,5‐tetrahydro[1]benzothieno[2′,3′:6,7]thiepino[4,5‐e]thiazolo[3,2‐c]pyrimidinium chloride ( 3c ) from the 2‐hydroxyethylamino‐derivative and 2‐hydroxyethylthio‐derivative, respectively. In contrast, 2‐hydroxyethoxy‐derivative ( 2b ) gave the rearrangement product, 3‐(2‐chloroethyl)‐5,6‐dihydro[1]benzothieno[3′,2′:2,3]thiepino[4,5‐d]pyrimidin‐4(3H)‐one ( 4 ). Effects of the synthesized compounds on collagen‐induced platelet aggregation were also evaluated.