Novel one pot synthesis of polysubstituted pyrazolo[1,5-a]- and imidazo[1,2-a]pyrimidines

Formation and Uses of Imidazo[1,2-a]pyrimidines and Related Compounds: A Review Comprising Years 2000-2021

This work covers the selected synthetic papers of imidazo[1,2-a]pyrimidine and its derivatives between the years 2000 and 2021. Synthesis of the heterocyclic moiety, application of this scaffold to biological activities, and secondary applications like corrosion inhibition are provided. The authors hope that readers will find the treatise useful.

Bicyclic 5-6 Systems: Comprehensive Synthetic Strategies for the Annulations of Pyrazolo[ 1,5-a]pyrimidines

Pyrazolopyrimidines are a privileged class of 5-6 bicyclic systems with three or four nitrogen atoms, including four possible isomeric structures. The significance of this class of compounds is that they can be applied in medical and pharmaceutical fields due to their unlimited biological aptitude, hence it is the basic skeleton of several synthetic drugs. The current review aimed to highlight all the synthetic routes that have been applied to construct the pyrazolo[1,5-a]pyrimidine ring systems up to date. The sections in this study included the synthesis of pyrazolo[1,5- a]pyrimidines by condensation reactions of 5-aminopyrazoles with each of β-diketones, 1,5-diketones, β- ketoaldehydes, α-cyanoaldehydes, β-enaminones, enamines, enaminonitriles, ethers, with unsaturated ketones, unsaturated thiones, unsaturated esters, unsaturated dienones "1,2-allenic", unsaturated aldehydes, unsaturated imines, and unsaturated nitriles. The routes adopted to synthesize this class of heterocyclic compounds were extended for ring construction from acyclic reagents and multicomponent reactions under catalytic or catalyst-free conditions.

Selective Metalation and Functionalization of Fluorinated Nitriles Using 2,2,6,6-Tetramethylpiperidyl Bases

We have accomplished regioselective deprotometalation of aromatic and heteroaromatic nitriles via (TMP)₂Zn·2MgCl₂·2LiCl and TMPMgCl·LiCl (TMP = 2,2,6,6-tetramethylpiperidyl) with the exploration of new and scarcely investigated metalation positions. Regioselectivity was rationalized by DFT calculations. The quenching of the generated organozinc and organomagnesium intermediates with various electrophiles gave access to 47 highly functionalized nitriles with yields up to 95%. Additionally, we report a difunctionalization strategy and the use of functionalized nitriles as building blocks to construct relevant heterocycles.

5-Amino-pyrazoles: potent reagents in organic and medicinal synthesis

5-Amino-pyrazoles have proven to be a class of fascinating and privileged organic tools for the construction of diverse heterocyclic or fused heterocyclic scaffolds. This review presents comprehensively the applications of 5-amino-pyrazoles as versatile synthetic building blocks in the synthesis of remarkable organic molecules with an emphasis on versatile functionalities. Following a brief introduction of synthesis methods, planning strategies to construct organic compounds, particularly diverse heterocyclic scaffolds, such as poly-substituted heterocyclic compounds and fused heterocyclic compounds via 5-amino-pyrazoles, have been summarized. Fused heterocycles are classified as bicyclic, tricyclic, tetracyclic, and spiro-fused pyrazole derivatives. These outstanding compounds synthesized via wide variety of approaches include conventional reactions, one-pot multi-component reactions, cyclocondensation, cascade/tandem protocols, and coupling reactions. 5-Amino-pyrazoles represent a class of promising functional reagents, similar to the biologically active compounds, highlighted with diverse applications especially in the field of pharmaceutics and medicinal chemistry. Notably, this critical review covers the articles published from 1981 to 2018.

Synthesis of 1H-azadienes and application to one-pot organic transformations

1H-Azadienes were synthesized from allyl azides by ruthenium catalysis under mild and neutral conditions. Applications of the 1H-azadienes were demonstrated for the one-pot synthesis of nitrogen containing organic compounds.

Synthetic approaches and functionalizations of imidazo[1,2-a]pyrimidines: an overview of the decade

This review gives an overview to the synthesis of the imidazo[1,2-a]pyrimidines on the basis of multicomponent reactions, condensation reactions, intramolecular cyclizations etc. along with its reactivity at 3-position.

Microwave-assisted palladium mediated efficient synthesis of pyrazolo[3,4-b]pyridines, pyrazolo[3,4-b]quinolines, pyrazolo[1,5-a]pyrimidines and pyrazolo[1,5-a]quinazolines

An efficient method was developed for the synthesis of pyrazole fused heterocycles via the palladium-catalyzed solvent free reaction of β-halovinyl/aryl aldehydes and 3-aminopyrazoles/5-aminopyrazoles under microwave irradiation in good yields.

Synthesis of Thieno[2,3-b]thiophene Containing Bis-Heterocycles-Novel Pharmacophores

Thioenethiophene derivatives represent an important class of compounds with diverse biological activities. We describe here the synthesis of a new series of thieno[2,3-b]thiophene containing bis-heterocyclic compounds 3–7. All the compounds were evaluated for their in vitro antioxidant potential, α-glucosidase and β-glucuronidase inhibiton and anticancer activity against PC-3 cell lines. Compounds 2b (IC₅₀ = 1.3 ± 0.2 μM), 5a (IC₅₀ = 2.3 ± 0.4 μM) and 5b (IC₅₀ = 8.7 ± 0.1 μM) showed a potent inhibition of β-glucuronidase enzyme, more active than the standard d-saccharic acid 1,4-lactone (IC₅₀ = 45.8 ± 2.5 μM). Compounds 5a (IC₅₀ = 22.0 ± 0.3 μM) and 5b (IC₅₀ = 58.4 ± 1.2 μM) were also found to be potent α-glucosidase inhibitors as compared to standard drug (acarbose, IC₅₀ = 841 ± 1.7 μM).

Synthesis of some new imidazo[3″,4″:1′,2′] pyrimido[4′,5′:4,5]thieno[2,3-c] pyridazines and other fused thieno[2,3-c]pyridazines

5-Amino-3,4-diphenylthieno[2,3-c]pyridazine-6-carboxamide was prepared and used as starting material to form the novel 6-chloromethyl-3,4-diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazin-8(7H)-one (3), the 6-(arylaminomethyl) compounds (4a–c), 7-aryl-7,8-dihydro-3,4-diphenylimidazo[3″,4″:1′,2′]pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazin-10(6H)-ones (5a–c), ethyl 7,8-dihydro-8-oxopyrimido[4′,5′:4,5]thieno[2,3-c]pyridazine-6-acetate (6) and its carbohydrazide (7). The pyridazinothienopyrimidotriazepinedione 8, pyridothienopyridazine 12 and pyridazinothienooxazepine 13 were also prepared.

1-Azadienes in cycloaddition and multicomponent reactions towards N-heterocycles

1-Azadienes are versatile building blocks for the efficient construction of various N-heterocycles. Depending on the substitution pattern and reaction partner, they may participate in a range of different reactions. An overview of recent methods for the generation of 1-azadienes is presented, as well as their application in cycloaddition, electrocyclization, and multicomponent reactions. Considering the broad range of reactivities and resulting heterocyclic scaffold structures, 1-azadienes are very useful reactive intermediates for the development of modular reaction sequences in diversity-oriented synthesis.