Synthesis of N‐(substituted phenylcarbonylamino)‐4‐ethyl‐1,2,3,6‐tetrahydropyridines as potential nonsteroidal anti‐inflammatory agents

Fourteen novel N‐(substituted phenylcarbonylamino)‐4‐ethyl‐1,2,3,6‐tetrahydropyridines 9 were synthesized in fair to good yields. 4‐Ethylpyridine 5 reacted with O‐mesitylenesulfonylhydroxylamine (O‐MSH) 4 to furnish N‐amino‐4‐ethylpyridinium mesitylenesulfonate 6 . The reaction of 6 with substituted acid chlorides 7 gave the stable crystalline pyridinium ylides 8a‐8n . A sodium borohydride reduction of 8 in absolute ethanol furnished the target compounds N‐(substituted phenylcarbonylamino)‐4‐ethyl‐1,2,3,6‐tetrahydropyridines 9a‐9n .     

Organocatalytic Enantioselective Oxidative CH Alkenylation and Arylation of N‐Carbamoyl Tetrahydropyridines and Tetrahydro‐β‐carbolines

The first organocatalytic enantioselective C? H alkenylation and arylation reactions of N‐carbamoyl tetrahydropyridines and tetrahydro‐β‐carbolines (THCs) are described. The metal‐free processes represent an efficient and straightforward approach to a variety of structurally and electronically diverse α‐substituted tetrahydropyridines and THCs in good yields with excellent regio‐ and enantioselectivities. Preliminary control experiments provide important insights into the reaction mechanism.     

Synthesis of Multifunctionalized 1,2,3,4‐Tetrahydropyridines, 2,3‐Dihydropyridin‐4(1H)‐ones,and Pyridines from Tandem Reactions Initiated by [5+1] Cycloaddition of N‐Formylmethyl‐Substituted Enamides to Isocyanides: Mechanistic Insight and Synthetic Application

Tandem reactions for the efficient synthesis of multifunctionalized 1,2,3,4‐tetrahydropyridines, 2,3‐dihydropyridin‐4(1H)‐ones, and pyridine derivatives have been developed and reaction mechanisms have been investigated. Synthetic cascades are initiated by the Zn(OTf)₂‐mediated [5+1] cycloaddition of N‐formylmethyl‐substituted tertiary enamides to isocyanides, thus leading to the versatile heterocyclic enamino imine intermediates. Interception of the intermediates by diastereoselective reduction of imine functionality with Me₄NBH(OAc)₃ afforded 1,6‐disubstituted trans‐3‐hydroxy‐4‐arylamino‐ or ‐alkylamino‐1,2,3,4‐tetrahydropyridines, whereas acylation of the imino group followed by acidic hydrolysis produced 1,6‐disubstituted 3‐acyloxy‐2,3‐dihydropyridin‐4(1H)‐ones. Aerobic oxidation led to the aromatization followed by intermolecular acyl‐group transfer from the pyridinium nitrogen to the 3‐hydroxy moiety, thereby yielding substituted 3‐acyloxy‐4‐aminopyridines. Synthetic potentials of the resulting products have been demonstrated by expedient and highly stereoselective synthesis of cis,cis‐4,5‐dihydroxy‐2‐phenylpiperidine and trans,trans‐4‐amino‐5‐hydroxy‐2‐phenylpiperidine compounds, which are important in medicinal chemistry, through simple and practical reduction reactions.     

Synthesis of Some New Heterocycles Derived from Ethyl 7‐Amino‐3‐(3‐methyl‐5‐oxo‐1‐phenyl‐2‐pyrazolin‐4‐yl)‐5‐aryl‐5H‐thiazolo[3,2‐a]pyrimidine‐6‐carboxylate of Biological Importance

Ethyl 7‐amino‐3‐(3‐methyl‐5‐oxo‐1‐phenyl‐2‐pyrazolin‐4‐yl)‐5‐aryl‐5H‐thiazolo[3,2‐a]pyrimidine‐6‐carboxylate was synthesized by the reaction of 4‐(2‐aminothiazol‐4‐yl)‐3‐methyl‐5‐oxo‐1‐phenyl‐2‐pyrazoline with arylidene ethyl cyanoacetate and it transformed to related fused heterocyclic systems via reaction with various reagents. The biological activities of these compounds were evaluated.     

Preparation and Reactions of 2‐Methyl‐7‐(3‐methyl‐5‐oxo‐1‐phenyl‐2‐pyrazolin‐4‐yl)‐5‐arylthiazolo[3,2‐a]‐pyrimido[4,5‐d]oxazin‐4(5H)‐one

Ethyl 7‐amino‐3‐(3‐methyl‐5‐oxo‐1‐phenyl‐2‐pyrazolin‐4‐yl)‐5‐aryl‐5H‐thiazolo[3,2‐a]pyrimidine‐6‐carboxylate was hydrolyzed with an ethanolic sodium hydroxide and the sodium salt thus formed underwent cyclization with acetic anhydride to afford 2‐methyl‐7‐(3‐methyl‐5‐oxo‐1‐phenyl‐2‐pyrazolin‐4‐yl)‐5‐arylthiazolo[3,2‐a]pyrimido[4,5‐d]oxazin‐4(5H)‐one. This compound was transformed to related heterocyclic systems via its reaction with various reagents. The biological activity of the prepared compounds was tested against Gram positive and Gram negative bacteria as well as yeast‐like and filamentous fungi. They revealed in some cases excellent biocidal properties.     

Halogenation of Fluorinated 1,3,5‐Triketones

The behavior of linear and cyclic fluorinated 1,3,5‐triketones and their metal derivatives towards common halogenating agents was examined, and optimal reaction conditions for the straightforward synthesis of mono‐, di‐, and tetrahalogenated products were found (Schemes 1–3). An aromatization through a double HBr elimination from an α,α′‐dibrominated cyclohexanone was shown to be a promising synthetic route to 1,1′‐(2‐hydroxy‐1,3‐phenylene)bis[2,2,2‐trifluoroethanones] (= 2,6‐bis(trifluoroacetyl)phenols; Scheme 4). Additionally, the 1,3,5‐triketones prepared add readily H₂O or alcohols to produce novel bridged 2,6‐dihydroxypyran‐4‐ones (Scheme 2). The structure of the obtained compounds 6a and 7a was confirmed by X‐ray structure analysis.     

Trifluoroacetic Anhydride Promoted Copper(I)‐Catalyzed Interrupted Click Reaction: From 1,2,3‐Triazoles to 3‐Trifluoromethyl‐Substituted 1,2,4‐Triazinones

A copper(I)‐catalyzed interrupted click reaction in the presence of trifluoroacetic anhydride has been developed, wherein an N‐trifluoroacetyl group is used to accelerate the ring‐opening of the putative 5‐copper(I) triazolide intermediate. Under the optimized reaction conditions, a broad range of azides and alkynes were found to participate in this transformation, thus affording 3‐trifluoromethyl‐substituted 1,2,4‐triazinones in moderate to excellent yields. The reaction has proven to be compatible with a variety of electron‐withdrawing and electron–donating groups, halogens, and nitrogen‐ and sulfur‐containing heterocycles, as well as pharmaceutically relevant molecules.     

Enantioselective Alkynylation of 2‐Trifluoroacetyl Imidazoles Catalyzed by Bis‐Cyclometalated Rhodium(III) Complexes Containing Pinene‐Derived Ligands

Chiral rhodium(III) complexes containing two cyclometalating 2‐phenyl‐5,6‐(S,S)‐pinenopyridine ligands and two additional acetonitriles are introduced as excellent catalysts for the highly enantioselective alkynylation of 2‐trifluoroacetyl imidazoles. Whereas the ligand‐based chirality permits the straightforward synthesis of the complexes in a diastereomerically and enantiomerically pure fashion, the metal‐centered chirality is responsible for the asymmetric induction over the course of the catalysis. For comparison, the analogous iridium congeners provide only low enantioselectivity, and previously reported benzoxazole‐ and benzothiazole‐based catalysts do not show any catalytic activity for this reaction under standard reaction conditions.     

Synthesis of 4‐Aryl‐8‐fluoro‐3a,4,5,9b‐tetrahydro‐3H‐cyclopenta[c]quinolines and Their Ozonides

4‐Aryl‐8‐fluoro‐3a,4,5,9b‐tetrahydro‐3H‐cyclopenta[c]quinolines are synthesized by acid‐catalyzed (CF₃CO₂H) three‐component cyclocondensation of 4‐fluoroaniline with aromatic aldehydes and cyclopentadiene. Stable ozonides with (1R*,4S*,5aR*,6S*,11bS*)‐configurations are obtained by ozonolysis of corresponding trifluoroacetyl derivatives.     

7‐Halogenated 7‐Deazapurine 2′‐Deoxyribonucleosides Related to 2′‐Deoxyadenosine, 2′‐Deoxyxanthosine,and 2′‐Deoxyisoguanosine: Syntheses and Properties

A series of 7‐fluorinated 7‐deazapurine 2′‐deoxyribonucleosides related to 2′‐deoxyadenosine, 2′‐deoxyxanthosine, and 2′‐deoxyisoguanosine as well as intermediates 4b – 7b, 8, 9b, 10b , and 17b were synthesized. The 7‐fluoro substituent was introduced in 2,6‐dichloro‐7‐deaza‐9H‐purine ( 11a ) with Selectfluor (Scheme 1). Apart from 2,6‐dichloro‐7‐fluoro‐7‐deaza‐9H‐purine ( 11b ), the 7‐chloro compound 11c was formed as by‐product. The mixture 11b / 11c was used for the glycosylation reaction; the separation of the 7‐fluoro from the 7‐chloro compound was performed on the level of the unprotected nucleosides. Other halogen substituents were introduced with N‐halogenosuccinimides ( 11a → 11c – 11e ). Nucleobase‐anion glycosylation afforded the nucleoside intermediates 13a – 13e (Scheme 2). The 7‐fluoro‐ and the 7‐chloro‐7‐deaza‐2′‐deoxyxanthosines, 5b and 5c , respectively, were obtained from the corresponding MeO compounds 17b and 17c , or 18 (Scheme 6). The 2′‐deoxyisoguanosine derivative 4b was prepared from 2‐chloro‐7‐fluoro‐7‐deaza‐2′‐deoxyadenosine 6b via a photochemically induced nucleophilic displacement reaction (Scheme 5). The pK_a values of the halogenated nucleosides were determined (Table 3). ¹³C‐NMR Chemical‐shift dependencies of C(7), C(5), and C(8) were related to the electronegativity of the 7‐halogen substituents (Fig. 3). In aqueous solution, 7‐halogenated 2′‐deoxyribonucleosides show an approximately 70% S population (Fig. 2 and Table 1).     

The First Fully Planar C5‐Conformation of Homooligopeptides Prepared from a Chiral α‐Ethylated α,α‐Disubstituted Amino Acid: (S)‐Butylethylglycine (=(2S)‐2‐Amino‐2‐ethylhexanoic Acid)

An optically active α‐ethylated α,α‐disubstituted amino acid, (S)‐butylethylglycine (=(2S)‐2‐amino‐2‐ethylhexanoic acid; (S)‐Beg; (S)‐ 2 ), was prepared starting from butyl ethyl ketone ( 1 ) by the Strecker method and enzymatic kinetic resolution of the racemic amino acid. Homooligopeptides containing (S)‐Beg (up to hexapeptide) were synthesized by conventional solution methods. An ethyl ester was used for the protection at the C‐terminus, and a trifluoroacetyl group was used for the N‐terminus of the peptides. The structures of tri‐ and tetrapeptides 5 and 6 in the solid state were solved by X‐ray crystallographic analysis, and were shown to have a bent planar C₅‐conformation (tripeptide) and a fully planar C₅‐conformation (tetrapeptide) (see Figs. 1 and 2, resp.). The IR and ¹H‐NMR spectra of hexapeptide 8 revealed that the dominant conformation in CDCl₃ solution was also a fully planar C₅‐conformation. These results show for the first time that the preferred conformation of homopeptides containing a chiral α‐ethylated α,α‐disubstituted amino acid is a planar C₅‐conformation.     

An Innovative Protocol for the Synthesis of 3‐(Pyridin‐2‐yl)‐5‐sec‐aminobiphenyl‐4‐carbonitriles and 9,10‐Dihydro‐3‐(pyridine‐2‐yl)‐1‐sec‐aminophenanthrene‐2‐carbonitriles

Herein, we present an innovative, novel, and highly convenient protocol for the synthesis of 3‐(pyridin‐2‐yl)‐5‐sec‐aminobiphenyl‐4‐carbonitriles ( 6a , 6b , 6c , 6d , 6e , 6f , 6g ) and 9,10‐dihydro‐3‐(pyridine‐2‐yl)‐1‐sec‐aminophenanthrene‐2‐carbonitriles ( 10a , 10b , 10c , 10d , 10e ), which have been delineated from the reaction of 4‐sec‐amino‐2‐oxo‐6‐aryl‐2H‐pyran‐3‐carbonitrile ( 4a , 4b , 4c , 4d , 4e , 4f , 4g ) and 4‐sec‐amino‐2‐oxo‐5,6‐dihydro‐2H‐benzo[h]chromene‐3‐carbonitriles ( 9a , 9b , 9c , 9d , 9e ) with 2‐acetylpyridine ( 5 ) through the ring transformation reaction by using KOH/DMF system at RT. The salient feature of this procedure is to provide a transition metal‐free route for the synthesis of asymmetrical 1,3‐teraryls like 3‐(pyridin‐2‐yl)‐5‐sec‐aminobiphenyl‐4‐carbonitriles ( 6a , 6b , 6c , 6d , 6e , 6f , 6g ) and 9,10‐dihydro‐3‐(pyridine‐2‐yl)‐1‐sec‐aminophenanthrene‐2‐carbonitriles ( 10a , 10b , 10c , 10d , 10e ). The novelty of the reaction lies in the creation of an aromatic ring from 2H‐pyran‐2‐ones and 2H‐benzo[h]chromene‐3‐carbonitriles via two‐carbon insertion from 2‐acetylpyridine ( 5 ) used as a source of carbanion.     

Facile synthesis of N‐α‐boc‐1,2‐dialkyl‐l‐histidines: Utility in the synthesis of thyrotropin‐releasing hormone (trh) analogs and evaluation of the cns activity

A facile synthesis of N‐α‐Boc‐1,2‐dialkyl‐L‐histidines starting from N‐α‐trifluoroacetyl‐L‐histidine methyl ester is reported. The key steps involve direct and regiospecific N‐1(τ) ring‐alkylation of the N‐α‐trifluoroacetyl‐L‐histidine‐methyl ester by suitable alkyl iodide in the presence of NaH in DMF at ?15 °C followed by homolytic free radical C‐2 alkylation via a silver catalyzed oxidative decarboxylation of alkylcarboxylic acid in the presence of ammonium persulfate under acidic conditions. The application of newly synthesized bioimidazoles was illustrated by their incorporation into thyrotropin‐releasing hormone (TRH). The synthesized TRH analogs were evaluated in vivo for analeptic activity. We report discovery of a TRH analog, which was found to potentiate the pentobarbital‐induced sleep in vivo.     

A simple synthesis of 5‐ethoxycarbonyl‐6‐phenyl‐1,3‐dioxin‐4‐ones and ethyl 3‐benzoyl‐4‐oxo‐2,6‐diphenylpyran‐5‐carboxylate

4‐Ethoxycarbonyl‐5‐phenyl‐2,3‐dihydrofuran‐2,3‐dione 1 reacts with aldehydes via the acylketene intermediate 2 giving the 1,3‐dioxin‐4‐ones 3a‐e and the 1,4‐bis(5‐ethoxycarbonyl‐4‐oxo‐6‐phenyl‐4H‐1,3‐dioxin‐2‐yl)benzene 4 , and a one step reaction between dibenzoylmethane and oxalylchloride gave 3,5‐dibenzoyl‐2,6‐diphenyl‐4‐pyrone 7 . The reaction of 1 with dibenzoylmethane, a dicarbonyl compound, provided ethyl 3‐benzoyl‐4‐oxo‐2,6‐diphenylpyran‐5‐carboxylate derivative 9 . Compound 9 was converted into the corresponding ethyl 3‐benzoyl‐4‐hydroxy‐2,6‐diphenylpyridine‐5‐carboxylate derivative 10 via its reaction with ammonium hydroxyde solution in 1 ‐butanol.     

One‐Pot Four‐Component Synthesis of N2‐Alkyl‐N3‐[2‐(1,3,4‐oxadiazol‐2‐yl)aryl]benzofuran‐2,3‐diamines

A simple synthesis of N²‐alkyl‐N³‐[2‐(1,3,4‐oxadiazol‐2‐yl)aryl]benzofuran‐2,3‐diamines 5 via a one‐pot four‐component reaction is described (Scheme 1). A mixture of N‐(isocyanoimino)triphenylphosphorane ( 1 ), a 2‐aminobenzoic acid 2 , a 2‐hydroxybenzaldehyde 3 , and an isocyanide 4 in absolute EtOH at room temperature undergoes a smooth reaction to afford 5 in excellent yields (Table).     

New domino‐reaction for the synthesis of N4‐(5‐aryl‐1,3‐oxathiol‐2‐yliden)‐2‐phenylquinazolin‐4‐amines and 4‐[4‐aryl‐5‐(2‐phenylquinazolin‐4‐yl)‐1,3‐thiazol‐2‐yl]morpholine

The model morpholine‐1‐carbothioic acid (2‐phenyl‐3H‐quinazolin‐4‐ylidene) amide (1) reacts with phenacyl bromides to afford N⁴‐(5‐aryl‐1,3‐oxathiol‐2‐yliden)‐2‐phenylquinazolin‐4‐amines (4) or N⁴‐(4,5‐diphenyl‐1,3‐oxathiol‐2‐yliden)‐2‐phenyl‐4‐aminoquinazoline ( 5 ) by a thermodynamically controlled reversible reaction favoring the enolate intermediate, while the 4‐[4‐aryl‐5‐(2‐phenylquinazolin‐4‐yl)‐1,3‐thiazol‐2‐yl]morpholine ( 8 ) was produced by a kinetically controlled reaction favoring the C‐anion intermediate. ¹H nmr, ¹³C nmr, ir, mass spectroscopy and x‐ray identified compounds ( 4 ), ( 5 ) and ( 8 ).     

Microwave‐induced Stereoselectivity in Synthesis of trans‐4‐Aryl‐3‐methyl‐6‐oxo‐4,5,6,7‐tetrahydro‐2H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitriles

A facile synthesis of trans isomers of 4‐aryl‐3‐methyl‐6‐oxo‐4,5,6,7‐tetrahydro ‐ 2H ‐ pyrazolo[3,4‐b]pyridine‐5‐carbonitriles via three‐component condensation reaction of an aldehyde, 3‐amino‐5‐methylpyrazole and ethyl cyanoacetate in acetonitrile has been developed under microwave irradiation. This one‐pot reaction proceeds without any catalyst in short times and gives the product in high selectivities and high yields.     

The Synthesis of New Heterocycles Using 2‐(4‐Chloro‐1,3‐dihydro‐3,3,7‐trimethyl‐2H‐indol‐2‐ylidene) Propanedial

4‐Chloro‐2,3,3,7‐tetramethyl‐3H‐indole (an indolenine) was produced by the reaction of 5‐chloro‐2‐methylphenylhydrazine hydrochloride with 3‐methylbutan‐2‐one via Fischer reaction. Exposure of the indolenine to the Vilsmeier reagent at 50°C produced a β‐diformyl compound, 2‐(4‐chloro‐1,3‐dihydro‐3,3,7‐trimethyl‐2H‐indol‐2‐ylidene)propanedial. This dialdehyde was reacted with arylhydrazines, acetamidinium chloride, urea, thiourea, guanidinium chloride, and cyanoacetamide to give various 5‐membered and 6‐membered heterocyclic products, each carrying a 4‐chloro‐3,3,7‐trimethyl‐3H‐indol‐2‐yl unit as a substituent, in excellent yields.     

One‐Pot Synthesis of 4‐(Alkylamino)‐1‐(arylsulfonyl)‐3‐benzoyl‐1,5‐ dihydro‐5‐hydroxy‐5‐phenyl‐2H‐pyrrol‐2‐ones via a Multicomponent Reaction

An effective route to novel 4‐(alkylamino)‐1‐(arylsulfonyl)‐3‐benzoyl‐1,5‐dihydro‐5‐hydroxy‐5‐phenyl‐2H‐pyrrol‐2‐ones 10 is described (Scheme 2). This involves the reaction of an enamine, derived from the addition of a primary amine 5 to 1,4‐diphenylbut‐2‐yne‐1,4‐dione, with an arenesulfonyl isocyanate 7 . Some of these pyrrolones 10 exhibit a dynamic NMR behavior in solution because of restricted rotation around the C? N bond resulting from conjugation of the side‐chain N‐atom with the adjacent α,β‐unsaturated ketone group, and two rotamers are in equilibrium with each other in solution ( 10 ? 11 ; Scheme 3). The structures of the highly functionalized compounds 10 were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS), by elemental analyses, and, in the case of 10a , by X‐ray crystallography. A plausible mechanism for the reaction is proposed (Scheme 4).     

Electro‐Oxidation of 3,4‐Dihydroxybenzoic Acid in the Presence of 6‐Methyl‐1,2,4‐Triazine‐3‐Thione‐5‐One: Unique Synthesis of 7H‐Thiazolo[3,2‐b]‐1,2,4‐Triazin‐7‐One Derivative in Aqueous Media

The electrochemical oxidation of 3,4‐dihydroxy benzoic acid ( 1 ) has been studied in the presence of 6‐methyl‐1,2,4‐triazine‐3‐thione‐5‐one ( 2 ) in aqueous solution. The oxidation mechanism of 1 and its reaction in the presence of 2 was offered. It was confirmed that 1 is converted to 7H‐thiazolo[3,2‐b]‐1,2,4‐triazin‐7‐one derivative 5 through Michael addition reaction of 2 to anodically generated o‐benzoquinone. The results of the research were used for electrochemical synthesis of 5 in an undivided cell in good yield and purity.