Lewis Acid Catalyzed Condensation–Cyclization Cascade: Direct Synthesis of Di/Trifluoromethyl‐1,2,3,4‐tetrahydroquinazolines

Condensed heterocycles such as quinazolines constitute the framework of many promising drugs. The great impact of the dramatic fluorine effect in pharmaceuticals prompted a great surge in the quest for fluorinated drug design resulting in over 20 % fluorine‐containing drugs in the market today. Therefore, finding an efficient and cost‐effective method for the direct synthesis of fluorine‐tagged quinazoline systems is of great significance in the pharmaceutical arena. For the first time, a one‐pot sequential condensation–cyclization reaction to form selectively the difluoro/trifluoromethylated tetrahydroquinazolines from simple components difluoro/trifluoroacetaldehyde hemiacetal and aromatic amines is reported. Our recent studies using difluoro/trifluoroacetaldehyde hemiacetal as simple and elegant difluoro/trifluoromethyl synthons and metal triflates such as gallium triflate as safe and stable Lewis acid catalysts led us to this direct synthesis protocol for the expedient and convenient synthesis of fluorinated quinazolines. DFT calculations at PCM/B3LYP/6‐31++G** were carried out for evaluating a possible reaction mechanism for this cyclization. According to the DFT calculations, product stereochemistry is thermodynamically driven, favoring the cis isomer as the major product, which is also confirmed experimentally.     

Development of a General Non‐Noble Metal Catalyst for the Benign Amination of Alcohols with Amines and Ammonia

The N‐alkylation of amines or ammonia with alcohols is a valuable route for the synthesis of N‐alkyl amines. However, as a potentially clean and economic choice for N‐alkyl amine synthesis, non‐noble metal catalysts with high activity and good selectivity are rarely reported. Normally, they are severely limited due to low activity and poor generality. Herein, a simple NiCuFeO_x catalyst was designed and prepared for the N‐alkylation of ammonia or amines with alcohol or primary amines. N‐alkyl amines with various structures were successfully synthesized in moderate to excellent yields in the absence of organic ligands and bases. Typically, primary amines could be efficiently transformed into secondary amines and N‐heterocyclic compounds, and secondary amines could be N‐alkylated to synthesize tertiary amines. Note that primary and secondary amines could be produced through a one‐pot reaction of ammonia and alcohols. In addition to excellent catalytic performance, the catalyst itself possesses outstanding superiority, that is, it is air and moisture stable. Moreover, the magnetic property of this catalyst makes it easily separable from the reaction mixture and it could be recovered and reused for several runs without obvious deactivation.     

A Novel Synthesis of Quinazolines by Cyclization of 1‐(2‐Isocyanophenyl)alkylideneamines Generated by the Treatment of 2‐(1‐Azidoalkyl)phenyl Isocyanides with NaH

A new and efficient method for the synthesis of quinazolines has been developed. Thus, N‐[2‐(1‐azidoalkyl)phenyl]formamides 1 are dehydrated with POCl₃ to give the corresponding 2‐(1‐azidoalkyl)phenyl isocyanides 2 , which are then treated with NaH in DMF at 0° to give quinazolines 6 in satisfactory yields via cyclization of 1‐(2‐isocyanophenyl)alkylideneamine intermediates 4 . This methodology can be applied to the synthesis of the 7‐azaanalogs of quinazolines, i.e., pyrido[3,4‐d]pyrimidines 9 .     

One Pot Synthesis of Medicinally Important cis‐2‐Methyl‐4‐amino substituted‐1,2,3,4‐tetrahydroquinolines

A simple synthesis of medicinally important cis‐2‐methyl‐4‐azapan‐2‐one‐1,2,3,4‐tetrahydroquinolines/cis‐9‐(2‐methyl‐1,2,3,4‐tetrahydroquinolin‐4‐yl)‐9H‐carbazole was reported. Multicomponent one pot synthesis with anilines and N‐vinylcaprolactam/N‐vinyl carbazole via imino Diels‐Alder reaction by using antimony trichloride as catalyst and acetonitrile as solvent was employed. NMR technique (2D) was used to study the regio‐ and stereo‐chemistry of newly synthesized compounds. The cis diastereo‐selectivity of the products was predicted by COSY and NOESY studies.     

An Efficient Three‐component,One‐pot Synthesis of Quinazolines under Solvent‐free and Catalyst‐free Condition

An efficient green protocol for the synthesis of quinazolines in the absence of solvent and catalyst has been developed. 2,4‐Disubstituted quinazolines have been synthesized from three‐component one‐pot reactions of 2‐aminoaryl ketones, orthoesters, and ammonium acetate. The present method has advantages of operational simplicity, substrate generality, clean reaction, high yields (76–94%), and moderate reaction time. The plausible mechanism of the reaction has been proposed based on the spectral characterization and single crystal X‐ray analysis of isolated intermediate.     

Synthesis of Quinoline and 1,2,3,4‐Tetrahydroquinoline Derivatives from Substituted o‐Nitrotoluenes via Cesium‐promoted [2 + 4] Cycloaddition

An atom economical highly efficient method has been developed for the synthesis of quinoline and 1,2,3,4‐tetrahydroquinoline derivatives from o ‐nitrotoluenes bearing electron‐withdrawing groups and olefins (acrylic esters, acrylonitriles, and methyl acrylates) via a base‐catalyzed [2 + 4] cycloaddition. This simple, rapid, and environment‐ friendly method provides a practical pathway for the synthesis of quinoline and 1,2,3,4‐tetrahydroquinoline derivatives. The starting materials are readily available and 37 products were obtained in good to excellent yields.     

A Simple One‐Pot Synthesis of N‐Alkyl‐2,5‐diaryl‐1,3‐dioxol‐4‐amines

An efficient procedure for the synthesis of N‐alkyl‐2,5‐diaryl‐1,3‐dioxol‐4‐amines 3 via a one‐pot reaction of aromatic aldehydes 2 and alkyl isocyanides 1 at room temperature in good yields is described (Scheme 1, Table).     

An Alternative Synthesis of the Dopaminergic Drug 2‐Amino‐1,2,3,4‐tetrahydronaphthalene‐5,6‐diol (5,6‐ADTN)

Racemic 2‐amino‐1,2,3,4‐tetrahydronaphthalene‐5,6‐diol (5,6‐ADTN; 4 ) was synthesized from 5,6‐dimethoxynaphthalene‐2‐carboxylic acid ( 14 ) in four steps (60% overall yield; Scheme). The crucial steps of the synthesis are Birch reduction of 14 to the valuable synthon 15 , Curtius reaction and carbamate formation ( 16 ), hydrogenolysis ( 17 ), and demethylation to the biologically active hydrobromide salt 18 of 4 .     

An Efficient One‐pot Synthesis of 2‐Amino‐5‐arylidenethiazol‐4‐ones Catalyzed by MgO Nanoparticles

A mild and efficient protocol for the synthesis of 2‐amino‐5‐arylidene‐1,3‐thiazol‐4(5H)‐ones is reported by three component reaction of aldehydes, rhodanine and secondary amines in the presence of magnesium oxide nanoparticles as heterogeneous nanocatalyst in good yields and short reaction times.     

Halogenoarylation of allyl isothiocyanate: Synthesis of 2,5‐disubstituted 2‐thiazolines

A new approach to the synthesis of 2‐R‐5‐benzyl‐2‐thiazolines with the use of chloro‐ and bromoarylation products of allyl isothiocyanate with arenediazonium halides was elaborated. The isothiocyanates obtained were reacted with ammonia, aliphatic or aromatic amines, and sodium methoxide. The use of ammonia or weakly basic amines in this reaction allowed. Intermediate thioureas to be isolated. On the basis of ¹H NMR spectra, amino–imino tautomerism of the synthesized 2,5‐disubstituted 2‐thiazolines were analyzed. 2‐Arylamino‐5‐benzyl‐2‐thiazolines exist mainly in the Z‐configuration of the imino form. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 517–525, 1999     

Synthesis of 4,6‐Dimethyldibenzothiophene and 1,2,3,4‐Tetrahydro‐4,6‐dimethyldibenzothiophene via Tilak Annulation

1,2,3,4‐Tetrahydro‐4,6‐dimethyldibenzothiophene was prepared by coupling 2‐bromo‐3‐methylcyclohexanone with 2‐methylbenzenethiol and annulating the product with the aid of polyphosphoric acid. A mixture of 1,2,3,4‐tetrahydro‐4,6‐dimethyldibenzothiophene and 4,6‐dimethyldibenzothiophene was prepared by coupling 2‐bromo‐3‐methylcyclohex‐2‐en‐1‐one with 2‐methylbenzenethiol and annulating the product with the aid of polyphosphoric acid. 2‐Bromo‐3‐methylcyclohexanone was synthesized by conjugate addition of Me₃Al to 2‐bromocyclohex‐2‐en‐1‐one with CuBr as catalyst and 2‐bromo‐3‐methylcyclohex‐2‐en‐1‐one by bromination? elimination of 3‐methylcyclohex‐2‐en‐1‐one. 1,2,3,4,4a,9b‐Hexahydro‐4,6‐dimethyldibenzothiophene was prepared by reduction of 1,2,3,4‐tetrahydro‐4,6‐dimethyldibenzothiophene with Zn and CF₃COOH.     

Synthesis and Thermal Behavior of a Fused,Tricyclic 1,2,3,4‐Tetrazine Ring System

This study presents the synthesis and characterization of a fused, tricyclic 1,2,3,4‐tetrazine ring system. The molecule is synthesized in a three‐step process from 5,5′‐dinitro‐bis,1,2,4‐triazole via a di‐N‐amino compound. Oxidation to form the azo‐coupled fused tricyclic 1,2,3,4‐tetrazine is achieved using tert‐butyl hypochlorite as the oxidant. The di‐N‐amino compound and the desired fused tricyclic 1,2,3,4‐triazine display interesting thermal behavior and are predicted to be high‐performance energetic materials.     

Highly Efficient Non‐Palladium‐Catalyzed Controlled Synthesis and X‐ray Analysis of Functionalized 1,2‐Diaryl‐, 1,2,3‐Triaryl‐, and 1,2,3,4‐Tetraarylbenzenes

A general, two‐step, highly efficient synthesis of 1,2‐diaryl‐, 1,2,3‐triaryl‐, and 1,2,3,4‐tetraarylbenzenes from simple stitching of α‐oxo‐ketene‐S,S‐acetals and active methylene compounds via a lactone intermediate is described. This procedure offers easy access to highly functionalized arylated benzenes that contain sterically demanding groups in good to excellent yields. The novelty of the procedure lies in the construction of aromatic compounds with the desired conformational flexibility along the molecular axis in a transition‐metal‐free environment through easily accessible precursors. Crystal analysis of these arylated benzene scaffolds showed that the peripheral aryl rings are arranged in a propeller‐like fashion with respect to the central benzene ring. Examination of the crystal packing in the structure of a 1,2,3,4‐tetraarylbenzene revealed an N???π interaction between molecules related by a two‐fold screw axis running in the direction of the a axis. Interestingly, the repeating array of N???π interactions around the axis of this 1,2,3,4‐tetraarylbenzene forces the molecules into a helical pattern.     

Synthesis and Thermal Behavior of a Fused,Tricyclic 1,2,3,4‐Tetrazine Ring System

This study presents the synthesis and characterization of a fused, tricyclic 1,2,3,4‐tetrazine ring system. The molecule is synthesized in a three‐step process from 5,5′‐dinitro‐bis,1,2,4‐triazole via a di‐N‐amino compound. Oxidation to form the azo‐coupled fused tricyclic 1,2,3,4‐tetrazine is achieved using tert‐butyl hypochlorite as the oxidant. The di‐N‐amino compound and the desired fused tricyclic 1,2,3,4‐triazine display interesting thermal behavior and are predicted to be high‐performance energetic materials.     

Synthesis of Pseudo‐Peptides Containing a Quinazolinone Skeleton via Ugi Four‐Component Reaction

A simple and efficient synthesis of quinazolinone pseudo‐peptide derivatives based on a new 3‐amino‐1,2,3,4‐tetrahydro‐4‐oxoquinazoline‐2‐carboxylic acid via Ugi four‐component reaction has been developed. This reaction was conducted under mild conditions with a broad scope of substrates.     

A one‐pot synthesis of 2‐aryl‐2,3‐dihydro‐4(lH)‐quinazolinones by use of samarium iodide

2‐Aryl‐2,3‐dihydro‐4(lH)‐quinazolines have been prepared in a one‐pot synthesis by samarium idoide (SmI₂) promoted reaction of o‐nitrobenzamide and aldehydes.     

Solid‐Phase Synthesis of 2‐Alkenamides from Polystyrene‐Supported α‐Selenocarboxylic Acids

The polystyrene‐supported α‐selenoacetic acid and α‐selenopropionic acid were prepared and used for the synthesis of 2‐alkenamides from primary and secondary amines in good yields and high purities.     

Polyoxometalate immobilized on MOF‐5 as an environment‐friendly catalyst for the synthesis of poly‐functionalized 3‐pyrrolin‐2‐ones

A polyoxometalate immobilized on MOF‐5 (POM/MOF‐5) material has been synthesized and evaluated for the diversity‐oriented synthesis of poly‐functionalized 3‐pyrrolin‐2‐ones via pseudo‐four‐component reaction between dialkyl acetylenedicarboxylate, amines, and aldehyde. The catalyst can be separated from the reaction mixture and reused at least five times with superior activity.     

The palladium‐catalyzed C‐N cross‐coupling reaction of diheteroaryl disulfides with heterocyclic amines

The Pd‐catalyzed cross‐coupling reaction of 1, 2‐di(pyrimidin‐2‐yl) disulfides with heterocyclic amines including 2‐amino pyrimidines and 1,3,4‐thiadiazol‐2‐amines to deliver symmetrical C‐N coupling products in moderate to good yields is reported. This method provides an opportunity for synthesis of bioactive molecules and pharmaceutically interesting compounds containing heterocycle motifs. The reported protocol shows good functional group compatibility, and provides a new strategy for preparation of C2‐amination pyrimidine derivatives from heterocyclic disulfides.     

A New and Convenient Synthesis of Amino‐phthalimide (1H‐Isoindole‐1,3(2H)‐dione) Derivatives and Their Photoluminescent Properties

A new and convenient synthesis for amino‐phthalimide (1H‐isoindole‐1,3(2H)‐dione) derivatives has been developed starting from an α,β‐unsaturated ketone. The ketones were reacted with amines to give aromatic amine products. This is the first time that substituted amine groups have been incorporated in aromatic rings. The mechanism of the product formation is rationalized by the 1,2‐addition of amines to ketones. All aromatic compounds exhibited high fluorescence properties at the blue‐green region.