Heterocyclic Synthesis

The reaction of N-phenylbenzamidine with O-acetylbenzeneoximoyl chloride in methanol solution gave
unexpectedly 5-methoxy-3,4,5-triphenyl-4,5-dihydro-1,2,4-oxadiazole, which structure was confirmed by
X-ray analysis. The last step of this reaction was simulated by the PM3 semiempirical method.

Ytterbium(III) triflate is an efficient and water-tolerant Lewis acid that has been used as a catalyst for a wide range of organic transformations. Various three-, four-, five-, and six-membered, as well as fused, heterocycles have been synthesized using ytterbium triflate as catalyst in both organic and aqueous solvents. The reaction conditions are relatively mild and the catalyst can be readily recovered from the reaction mixtures to be reused.

A green approach for the synthesis of polyfunctionalized pyrrolo[2,3-d]pyrimidine derivatives was successfully achieved by a one-pot three-component reaction of arylglyoxals, 6-amino-1,3-dimethyluracil and barbituric acid derivatives in the presence of tetra-n-butylammonium bromide (TBAB) (5 mol%) as the catalyst in ethanol at 50 °C. This protocol has many advantages such as high yields (73-95%), green and simple procedure, short reaction times, easy work-up, mild reaction conditions and general applicability.

One of the topical research areas dealing with Pd-catalyzed cross-coupling reactions is the development of regenerable catalytic systems through immobilization of highly active palladium complexes, clusters or nanoparticles onto an inert support. In the context of increased environmental requirements, highly active and multiply reusable heterogeneous catalytic systems have a number of practical advantages over homogeneous analogues. In this review, various approaches to immobilization on a polystyrene support of N-heterocyclic carbene and acyclic diaminocarbene palladium complexes have been considered for the first time; these complexes are a promising alternative to the widely used phosphine complexes. Special attention focuses on modern physicochemical methods used for investigation of corresponding heterogeneous systems. In addition, examples are given of using reusable heterogeneous catalysts for Sonogashira–Hagihara and Suzuki–Miyaura reactions, with emphasis on the true nature of the palladium catalytic species.
The bibliography includes 83 references.

Various diazotized aryl amines were coupled with N-(4-nitrophenyl)-2-[(4-phenyl-1,3-thiazol-2-yl)amino]acetamide to give the
corresponding various azo disperse dyes (D1-D13). ese dyes were applied to polyester 􀄕ber by HTHP method and their fastness
properties were evaluated. Dyes were characterized by IR, elemental analysis, and NMR spectral studies. ese dyes showed very
good antibacterial and antifungal activities.

A series of heterocyclic compounds incorporating pyridazine moiety were for diverse biological activities. Pyridazines and pyridazinones derivatives showed wide spectrum of biological activities such as vasodialator, cardiotonic, anticonvulsant, antihypertensive, antimicrobial, anti-inflammatory, analgesic, anti-feedant, herbicidal, and various other biological, agrochemical and industrial chemical activities. The results illustrated that the synthesized pyridazine/pyridazine compounds have diverse and significant biological activities. Mechanistic insights into the biological properties of pyridazinone derivatives and various synthetic techniques used for their synthesis are also described.

The morpholine (1,4-oxazinane) motif attracted significant attention due to its widespread availability in natural products and biologically relevant compounds. This review describes recent advances in the synthesis of morpholines and their carbonyl-containing analogs from 1,2-amino alcohols, aziridines, epoxides, and related compounds. Special attention is paid to the syntheses performed in a stereoselective manner and using transition metal catalysis. Selected works published since 2013 are covered.

Research in the field of aerobic oxidation has recently gained much attention from both academia and industry. The main reason for this has to be found in the inherent greenness of such methods. Although much investigation has been undertaken to develop new methods and reactions and to elucidate the mechanistic aspects of this chemistry, its applications in the synthesis of heterocycles have been relatively limited. In this review, the recent developments in this field are summarized.

Three-component reaction of 3-amino-1H-1,2,4-triazole or 5-amino-2H-1,2,3-triazole derivatives, acetaldehyde, and 1,3-dicarbonyl compounds (acetylacetone or β-keto esters) in water under microwave irradiation leads to regioselective formation of 4,7-dihydro[1,2,4]- triazolo- and 4,7-dihydro[1,2,3]triazolo[1,5-a]pyrimidines. Using ethyl 4,4,4-trifluoro-3-oxobutanoate as 1,3-dicarbonyl compound under the same conditions allows to obtain the corresponding 5-hydroxy-4,5,6,7-tetrahydro derivatives, which fail to dehydrate in the reaction medium.

Three-component heterocyclizations of pyruvic acids and their esters with 5-aminopyrazoles and aromatic aldehydes, in addition to the sequential versions of these reactions, under different activating conditions were studied. Under conventional heating, pyrazolopyrimidine derivatives containing a hy-droxyl group in the 6-position were formed in both two-and three-component treatments. Whereas the application of an inert atmosphere did not influence the outcome of these reactions, the use of ultrasonic irradiation led to the formation of 7-hydroxy-tetrahydropyrazolopyrimidines in multi-component reactions and 6-hydroxy-dihydropyrazolopyrimidines in the case of a step-by-step approach. The products of the latter treatment were further transformed into heteroaromatized 6-hydroxy-pyrazolopyrimidines by conventional heating.

In this work, new Schiff bases, their acetyl oxadiazole, and azetidinone derivatives derived from
pyromelliticdiimide were synthesized via multistep synthesis. In the first step, pyromelliticdiimide
[1] was prepared via reaction of pyromelliticdianhydride with urea either under conventional
heating or microwave irradiation.
In the second step, compound [1] was converted into its potassium salt [2] by treatment with
alcoholic KOH solution.Inthe third step compound [2] was introduced in reaction with ethyl
chloroacetate producing compound [3] ethyl -2- (N-pyromelliticdiimidyl) acetate. Compound [3] was
introduced in reaction with hydrazine hydrate as a fourth step affording compound [4] 2- (N-
(pyromelliticdiimidyl)) acetohydrazide.
Acid – catalyzed condensation reaction of compound [4] with aromatic aldehydes afforded new three
Schiff bases [5-7]. The newly synthesized Schiff bases [5] and [6] were introduced in reaction with
chloroacetyl chloride producing new two azetidinones derivatives [8] and [9]. Introducing of the
newly prepared Schiff base [6] in reaction with acetic anhydride afforded new acetyl oxadiazole
derivatives [10]. Antimicrobial activity of some prepared compounds against different types of
bacteria and fungi were evaluated and showed promising results.

This microreview summarizes data published over the past 10 years devoted to the synthesis of substituted 2,1-benzisoxazoles. The major synthetic approaches aim at increasing either the electrophilicity or nucleophilicity of ortho substituents or other substrates. Ortho-substituted aryl azides, anilines, nitroso- and nitrobenzenes were used as starting compounds.

Novel 1,4-benzoxazine derivatives were synthesized by an efficient and simple method in high yields. Readily available starting materials, operational simplicity, mild reaction conditions and novelty are the key advantages of this method. The synthetically attractive feature of the procedure is reflected by its applicability to a wide range of isatin and aniline derivatives. Besides their novel structures, these compounds may have important biological activities and industrial applications. Furthermore, we demonstrated that in BaeyereVilliger oxidation reaction, the phenyl group migrate better than amidine groups but not as good as amide group. The migratory ability for these groups in BaeyereVilliger oxidation reaction is ranked amide > phenyl > amidine.

The chloride ion catalysed addition of SCl2 to TCNE gives the dicyanomethylene-1,2,6-thiadiazine 3 as major product together with two unexpected minor products, pyrimidine 4 and pyrroloimidazothiadiazine 5, whose X-ray crystal structures are described; the products are derived from interaction of SCl2 with one cyano group with neighbouring group participation by two others.

Four-component reactions of 3-amino-1,2,4-triazole or 5-amino-1H-pyrazole-4-carbonitrile with aromatic aldehydes and pyruvic acid or its esters under ultrasonication were studied. Unusual for such a reaction type, a cascade of elementary stages led to the formation of 7-azolylaminotetrahydroazolo[1,5-a]pyrimidines.