A Simple Synthesis of 2‐{(Arylmethylidene)hydrazinylidene]‐3‐hydroxy‐4H‐furo[3,2‐c]pyran‐4(3H)‐ones

A simple synthesis of 2‐hydrazinylidene‐3‐hydroxy‐4H‐furo[3,2‐c]pyran‐4‐ones is described. A mixture of (isocyanoimino)(triphenyl)phosphorane, an aromatic aldehyde, and dehydroacetic acid (=3‐acetyl‐2‐hydroxy‐6‐methyl‐4H‐pyran‐4‐one) undergo a 1 : 1 : 1 addition reaction under mild conditions to afford the title compounds in excellent yields.     

Fast Efficient and General PASE Approach to Medicinally Relevant 4H,5H‐Pyrano‐[4,3‐b]pyran‐5‐one and 4,6‐Dihydro‐5H‐pyrano‐[3,2‐c]pyridine‐5‐one Scaffolds

The general ‘on‐solvent’ PASE approach was found to be medicinally relevant for 4H,5H‐pyrano[4,3‐b]pyran‐5‐one and 4,6‐dihydro‐5H‐pyrano[3,2‐c]pyridine‐5‐one scaffolds. Ammonium acetate‐catalyzed multicomponent reaction of aldehydes and two different C–H acids in the presence of small amounts of EtOH results in fast (3 – 15 min) and efficient formation of scaffolds, promising for many diverse oriented medical applications.     

Reactions of Imidoyl Isoselenocyanates with Aromatic 2‐Amino N‐Heterocycles and 1‐Methyl‐1H‐imidazole

The reaction of N‐phenylimidoyl isoselenocyanates 1 with 2‐amino‐1,3‐thiazoles 10 in acetone proceeded smoothly at room temperature to give 4H‐1,3‐thiazolo[3,2‐a] [1,3,5]triazine‐4‐selones 13 in fair yields (Scheme 2). Under the same conditions, 1 and 2‐amino‐3‐methylpyridine ( 11 ) underwent an addition reaction, followed by a spontaneous oxidation, to yield the 3H‐4λ⁴‐[1,2,4]selenadiazolo[1′,5′:1,5] [1,2,4]selenadiazolo[2,3‐a]pyridine 14 (Scheme 3). The structure of 14 was established by X‐ray crystallography (Fig. 1). Finally, the reaction of 1‐methyl‐1H‐imidazole ( 12 ) and 1 led to 3‐methyl‐1‐(N‐phenylbenzimidoyl)‐1H‐imidazolium selenocyanates 15 (Scheme 4). In all three cases, an initially formed selenourea derivative is proposed as an intermediate.     

Synthesis and Reactions of 2‐[1‐Methyl‐1‐(pyrrolidin‐2‐yl)ethyl]‐1H‐pyrrole and Some Derivatives with Aldehydes: Chiral Structures Combining a Secondary‐Amine Group with an 1H‐Pyrrole Moiety as Excellent H‐Bond Donor

The synthesis of compound 2 and its derivatives 6 and 8 combining a pyrrolidine ring with an 1H‐pyrrole unit is described (Scheme 2). Their attempted usability as organocatalysts was not successful. Reacting these simple pyrrolidine derivatives with cinnamaldehyde led to the tricyclic products 3b, 9b , and 10b first (Scheme 1, Fig. 2). The final, major products were the pyrrolo‐indolizidine tricycles 3a, 9a , and 10a obtained via the iminium ion reacting intramolecularly with the nucleophilic β‐position of the 1H‐pyrrole moiety (cf. Scheme 1).     

The Stereoselective Total Synthesis of (6S)‐5,6‐Dihydro‐6‐[(2R)‐2‐hydroxy‐6‐phenylhexyl]‐2H‐pyran‐2‐one via Prins Cyclization

The stereoselective total synthesis of an antiproliferative and antifungal α‐pyrone natural product (6S)‐5,6‐dihydro‐6‐[(2R)‐2‐hydroxy‐6‐phenylhexyl]‐2H‐pyran‐2‐one is described. The key steps involved are the Prins cyclization, Mitsunobu reaction, and ring‐closing metathesis reaction.     

Reactions of 2‐Unsubstituted 1H‐Imidazole 3‐Oxides with 2,2‐Bis(trifluoromethyl)ethene‐1,1‐dicarbonitrile: A Stepwise 1,3‐Dipolar Cycloaddition

The reaction of 1,4,5‐trisubstituted 1H‐imidazole‐3‐oxides 1 with 2,2‐bis(trifluoromethyl)ethene‐1,1‐dicarbonitrile ( 7 , BTF) yielded the corresponding 1,3‐dihydro‐2H‐imidazol‐2‐ones 10 and 2‐(1,3‐dihydro‐2H‐imidazol‐2‐ylidene)malononitriles 11 , respectively, depending on the solvent used. In one example, a 1 : 1 complex, 12 , of the 1H‐imidazole 3‐oxide and hexafluoroacetone hydrate was isolated as a second product. The formation of the products is explained by a stepwise 1,3‐dipolar cycloaddition and subsequent fragmentation. The structures of 11d and 12 were established by X‐ray crystallography.     

The Structures of Indazolin‐3‐one (=1,2‐Dihydro‐3H‐indazol‐3‐one) and 7‐Nitroindazolin‐3‐one

The existence of polymorphism in parent indazolin‐3‐one (=1,2‐dihydro‐3H‐indazol‐3‐one; 1 ) is reported as well as an X‐ray and NMR CPMAS study establishing that its 7‐nitro derivative 2 exists as the 3‐hydroxy tautomer. Absolute shieldings calculated at the GIAO/B3LYP/6‐311++G(d,p) level were used to determine the tautomeric oxo/hydroxy equilibrium in solution, i.e., always the 1H‐indazol‐3‐ol tautomer predominates.     

Synthesis and Asymmetric Oxidation of (Caranylsulfanyl)‐1H‐imidazoles

For the first time 2‐(cis‐caran‐4‐ylsulfanyl)‐1H‐imidazole, 1‐methyl‐2‐(cis‐caran‐4‐ylsulfanyl)‐1H‐imidazole, and 2‐(cis‐caran‐4‐ylsulfanyl)‐1H‐benzimidazole (carane=3,7,7‐trimethylbicyclo[4.1.0]heptane) were synthesized, and the asymmetric oxidation of these compounds was also carried out. It was shown that oxidation by the Bolm system and the modified system of Sharpless lead to corresponding sulfoxides with de values of 91–100%.     

Synthesis of 1,3‐Selenazol‐2(3H)‐imines

The reaction of N,N′‐diarylselenoureas 16 with phenacyl bromide in EtOH under reflux, followed by treatment with NH₃, gave N,3‐diaryl‐4‐phenyl‐1,3‐selenazol‐2(3H)‐imines 13 in high yields (Scheme 2). A reaction mechanism via formation of the corresponding Se‐(benzoylmethyl)isoselenoureas 18 and subsequent cyclocondensation is proposed (Scheme 3). The N,N′‐diarylselenoureas 16 were conveniently prepared by the reaction of aryl isoselenocyanates 15 with 4‐substituted anilines. The structures of 13a and 13c were established by X‐ray crystallography.     

Synthesis of Furo[2,3‐d]pyridazin‐4(5H)‐one and Its N(5)‐Substituted Derivatives

We report the efficient preparation of furo[2,3‐d]pyridazin‐4(5H)‐one and its N‐substituted derivatives starting from methyl 2‐methylfuran‐3‐carboxylate. The Me group was converted to the aldehyde group, which was then condensed with hydrazine derivatives. Then, the ester functionalities were hydrolyzed to the corresponding acids, followed by treatment with SOCl₂ to give N‐substituted furopyridazinone derivatives.     

A Convenient Method for the Preparation of 1,5‐Diaryl‐3‐(arylamino)‐1H‐pyrrol‐2(5H)‐ones

A simple and eco‐friendly method for the preparation of 1,5‐diaryl‐3‐(arylamino)‐1H‐pyrrol‐2(5H)‐ones via the cyclo‐condensation reaction of aldehydes, amines and ethyl pyruvate in the presence of silica supported ferric chloride (SiO₂‐FeCl₃) as reusable heterogeneous catalyst is described. The present methodology offers several advantages such as excellent yields, simple procedure and short reaction times.     

Transformation of 5‐Hydroxy‐ to (5‐Chloropentanoyl)amino Derivatives under ‘Direct Amide Cyclization’ Conditions

The application of the ‘direct amide cyclization’ conditions to the linear δ‐hydroxy diamide 11 is described (Scheme 3). Instead of the cyclization to the expected nine‐membered cyclodepsipeptide, only the chloro acid 12 was obtained. Its formation could be explained by consecutive formation of the 1,3‐oxazol‐5(4H)‐one 16 and the six‐membered imino lactone 17 as intermediates (Scheme 4). The spontaneous isomerization of the latter gave 12 in a good yield.     

Nitration Products of 5‐Amino‐1H‐tetrazole and Methyl‐5‐amino‐1H‐tetrazoles – Structures and Properties of Promising Energetic Materials

The nitration of 5‐amino‐1H‐tetrazole ( 1 ), 5‐amino‐1‐methyl‐1H‐tetrazole ( 3 ), and 5‐amino‐2‐methyl‐2H‐tetrazole ( 4 ) with HNO₃ (100%) was undertaken, and the corresponding products 5‐(nitrimino)‐1H‐tetrazole ( 2 ), 1‐methyl‐5‐(nitrimino)‐1H‐tetrazole ( 5 ), and 2‐methyl‐5‐(nitramino)‐2H‐tetrazole ( 6 ) were characterized comprehensively using vibrational (IR and Raman) spectroscopy, multinuclear (¹H, ¹³C, ¹⁴N, and ¹⁵N) NMR spectroscopy, mass spectrometry, and elemental analysis. The molecular structures in the crystalline state were determined by single‐crystal X‐ray diffraction. The thermodynamic properties and thermal behavior were investigated by using differential scanning calorimetry (DSC), and the heats of formation were determined by bomb calorimetric measurements. Compounds 2, 5 , and 6 were all found to be endothermic compounds. The thermal decompositions were investigated by gas‐phase IR spectroscopy as well as DSC experiments. The heats of explosion, the detonation pressures, and velocities were calculated with the software EXPLO5, whereby the calculated values are similar to those of common explosives such as TNT and RDX. In addition, the sensitivities were tested by BAM methods (drophammer and friction) and correlated to the calculated electrostatic potentials. The explosion performance of 5 was investigated by Koenen steel sleeve test, whereby a higher explosion power compared to RDX was reached. Finally, the long‐term stabilities at higher temperatures were tested by thermal safety calorimetry (FlexyTSC). X‐Ray crystallography of monoclinic 2 and 6 , and orthorhombic 5 was performed.     

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.     

A One‐Pot Biginelli Synthesis of 6‐Unsubstituted 5‐Aroylpyrimidin‐2(1H)‐ones and 6‐Acetyl‐1,2,4‐triazin‐3(2H)‐ones

The three‐component Biginelli‐like cyclocondensation reaction of enamines 1 , urea, and aldehydes in dioxane/acetic acid efficiently afforded the corresponding 6‐unsubstituted 3,4‐dihydropyrimidin‐2(1H)‐ones 2 in good yields (Scheme 1, Table). The corresponding reaction of azaenamine (=hydrazone) 7 with benzaldehyde and urea afforded 6‐acetyl‐1,2,4‐triazin‐3(2H)‐ones in good yields (Scheme 3).     

Efficient One‐Pot Synthesis of Alkyl 2‐(Dialkylamino)‐4‐phenylthiazole‐5‐carboxylates and Single‐Crystal X‐Ray Structure of Methyl 2‐(Diisopropylamino)‐4‐phenylthiazole‐5‐carboxylate

The reaction between secondary amines, benzoyl isothiocyanate, and dialkyl acetylenedicarboxylates (=dialkyl but‐2‐ynedioates) in the presence of silica gel (SiO₂) led to alkyl 2‐(dialkylamino)‐4‐phenylthiazole‐5‐carboxylates in fairly high yields. The structures of the products were confirmed by their IR, ¹H‐ and ¹³C‐NMR, and mass spectra, and by a single‐crystal X‐ray structure determination.     

Synthesis of 4‐((2‐hydroxynaphthalen‐1‐yl)(aryl)methyl)‐5‐methyl‐2‐phenyl‐1H‐pyrazol‐3(2H)‐ones using nano‐Zn‐[2‐boromophenyl‐salicylaldimine‐methylpyranopyrazole]Cl2 nanoparticles

Nano‐Zn‐[2‐boromophenyl‐salicylaldimine‐methylpyranopyrazole]Cl₂ (nano‐[Zn‐2BSMP]Cl₂) as a nanoparticle Schiff base complex and a catalyst was introduced for the solvent‐free synthesis of 4‐((2‐hydroxynaphthalen‐1‐yl)(aryl)methyl)‐5‐methyl‐2‐phenyl‐1H‐pyrazol‐3(2H)‐ones by the multicomponent condensation reaction of various aromatic aldehydes, β‐naphthol, ethyl acetoacetate, and phenyl hydrazine at room temperature.     

Synthesis of Macrocyclic Lactones via Ring Transformation of 4‐(ω‐Hydroxyalkyl)‐1,3‐oxazol‐5(4H)‐ones

The synthesis of α‐benzamido‐α‐benzyl lactones 23 of various ring size was achieved either via ‘direct amide cyclization’ by treatment of 2‐benzamido‐2‐benzyl‐ω‐hydroxy‐N,N‐dimethylalkanamides 21 in toluene at 90 – 110° with HCl gas or by ‘ring transformation’ of 4‐benzyl‐4‐(ω‐hydroxyalkyl)‐2‐phenyl‐1,3‐oxazol‐5(4H)‐ones under the same conditions. The precursors were obtained by C‐alkylations of 4‐benzyl‐2‐phenyl‐1,3‐oxazol‐5(4H)‐one ( 15 ) with THP‐ or TBDMS‐protected ω‐hydroxyalkyl iodides. Ring opening of the THP‐protected oxazolones by treatment with Me₂NH followed by deprotection of the OH group gave the diamides 21 , whereas deprotection of the TBDMS series of oxazolones 25 with TBAF followed by treatment with HCl gas led to the corresponding lactones 23 in a one‐pot reaction.     

Photocycloaddition Reactions of 2‐(Alk‐3‐en‐1‐ynyl)cyclohex‐2‐enones

The newly synthesized 2‐(alk‐3‐en‐1‐ynyl)cyclohex‐2‐enones 4 undergo photodimerization (chemo‐ and regio‐)selectively at the exocyclic C?C bond to give diastereoisomeric mixtures of 1,2‐dialkynyl‐1,2‐dimethylcyclobutanes. On irradiation of 4 in the presence of 2‐chloroacrylonitrile, cyclobutane formation occurs again (chemo‐ and regio‐)selectively at the exocyclic C?C bond to afford diastereoisomeric mixtures of 2‐alkynyl‐1‐chloro‐2‐methylcyclobutanecarbonitriles. Similarly, compounds 4 undergo photoaddition to 2,3‐dimethylbuta‐1,3‐diene exclusively at the exocyclic C?C bond to afford mixtures of [2+2] and [4+2] cycloadducts.     

Tautomeric behaviour and isotopic multiplets in the 13C NMR spectra of partially deuterated 5‐arylazo‐pyrimidine (1H,3H,5H)‐2,4,6‐triones and 5‐arylazo‐2‐thioxo‐pyrimidine (1H,3H,5H)‐4,6‐diones—evidence for elucidation of tautomeric forms

NMR spectra of the synthesized azo dyes, 5‐arylazo‐pyrimidine (1H,3H,5H)‐2,4,6‐triones (5a–g), 1,3‐dimethyl‐5‐arylazo‐pyrimidine (1H,3H,5H)‐2,4,6‐triones (6a–g), and 5‐arylazo‐2‐thioxo‐pyrimidine (1H,3H,5H)‐4,6‐diones (7a–g) were studied in (CD₃)₂SO (three drops of CD₃OD were added into solutions of the dyes in two different concentrations). All dyes showed intramolecular hydrogen bonding. Dyes 5a–7a showed bifurcated intramolecular hydrogen bonds. Tautomeric behaviours of some of N‐methylated azo dyes (6a‐g) were studied in two different concentrations. The solvent–substrate proton exchange of dyes 5a–d, 6a and 7a–e was examined in presence of three drops of CD₃OD. The dyes which were soluble in (CD₃)₂SO containing CD₃OD showed isotopic splitting (β‐isotope effect) in the ¹³C NMR spectra. Copyright © 2009 John Wiley & Sons, Ltd.