Role of Microwaves in the Synthesis of Fused Five-Membered Heterocycles with Three N-Heteroatoms

Abstract

The development of new strategies for the synthesis of small-sized heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in three nitrogen atoms containing fused five membered heterocyclic compounds synthesis is presented, focusing on the developments in the last 5-10 years. This contribution covers the literature concerning the total synthesis of N,N,N-heterocycles. The literature data are summarized based on the type of cycles.

Recent Advances in the Synthesis of 5‐MemberedN‐Heterocycles via Rhodium Catalysed Cascade Reactions

“…[108] β-N-Glycosyl indoles are typically found in natural products exhibiting remarkable biological activities. [109a] Earlier reports display synthesis of 2,3-substituted β-N-glycosyl indoles via (i) multistep reaction between indoline derivatives with sugar lactols, [109b,c] (ii) β-glycosylation of indoles through a SN 2 Mitsunobu reaction, [109d-f] and (iii) danishefsky epoxide-opening of α-1,2-anhydro sugars. [ 109g] Zhao and co-workers, in 2020 disclosed an efficient and selective CÀ H activation method of readily available β-N-aryl glycosides 180 with various alkynes 181, synthesizing a variety of 2,3-substituted N-glycosylindoles 182 in good yields using [Cp*RhCl 2 ] 2 as catalyst.…”

“…[33h-n] Cycloaddition/cyclization of highly reactive carbonyl yildes provided oxacycles or epoxides. [33h-j,o] Allyl-substituted oxonium ylides on [2,3]-sigmatropic rearrangements forms homoallyl ethers. [33k,l] The ylides of aldehydes and ketones are well explored on intermolecular reaction with carbenes.…”

“…The basis of many drugs like Captopril (Hypertension), Morphine (Analgesic), and Vincristine (Cancer Chemotherapy) are nitrogen containing heterocycles [1] . Aromatic five‐membered N ‐heterocycles containing one to four nitrogen atoms include pyrroles, pyrazoles, imidazoles, triazoles, tetrazoles, oxazoles, isoxazoles, and oxadiazoles [2] . Pyrrole containing pharmaceutical compounds acts as fungicides, antibiotics, anti‐inflammatory drugs, [3] cholesterol reducing drugs, anti‐tumor agents, [4] anti‐microbial and many more [5a] .…”

“…[1] Aromatic five-membered N-heterocycles containing one to four nitrogen atoms include pyrroles, pyrazoles, imidazoles, triazoles, tetrazoles, oxazoles, isoxazoles, and oxadiazoles. [2] Pyrrole containing pharmaceutical compounds acts as fungicides, antibiotics, anti-inflammatory drugs, [3] cholesterol reducing drugs, anti-tumor agents, [4] anti-microbial and many more. [5a] N-heterocycles are currently a hot topic in modern drug discovery and designing programs due to their biological importance and the advancement in the synthetic methodologies.…”

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“…Therefore, it is appealing to develop the corresponding strategy for the green synthesis of the 4-Aryl-2-hydra-zinothiazole nucleus of the proposed research [12][13][14][15] . Many attempts were carried out to prepare 1-(4-mtolylthiazol-2-yl)hydrazine (B) where R = CH 3 for derivatives prepared, the first attempt was carried out by the conventional method under reflux for 2hrs., by refluxing thiocarbohydrazide with, 2bromo-1-p-tolylethanone in glacial acetic acid 16,17,18,19 . Where the second method was carried out using microwave free reaction for 1.5-2 min, using the two above compounds without any solvents or liquid media 20 .…”