Heterocyclic compounds form a major class of compounds in chemistry. There has been considerable interest in the development of novel heterocyclic compounds with varied biological activities. Azoles are famous and widespread scaffold in the pharmaceutical industry due to their range of activities. Diazocarbonyl compounds have found numerous applications in many areas of chemistry. Among the most developed fields of diazo compounds. This approach represents a useful alternative to more conventional methods of the synthesis of azoles. The present review discussed the different characteristics of the azoles of interest, to recognize the differences in pharmacolog, safety, toxicity and potential drug interactions of these antifungal agents.
Introduction
I. INTRADUCTION
Azoles are the famous and widespread scaffold in the pharmaceutical industry due to their wide range of activities, high efficiency, good tolerability, and oral availability .Furthermore, azole derivatives have attracted attention as potent antimicrobial agents. The purpose of this review is to provide an overview of pharmacological aspects of the main scaffolds of azoles, including imidazole, triazol, and tetrazole, which possess antimicrobial activity. Diazo compounds are incredibly useful reagents in synthetic organic chemistry due to their extremely versatile and unique reactivity.
Recently, a range of new methods have been developed for the synthesis of various heterocycles from diazo compounds, some of which are described in review. Versatility and efficiency of diazo compounds are most clearly manifested in the synthesis of azoles—five-membered heterocycles containing a nitrogen atom and at least one other non-carbon atom of either nitrogen , oxygen, or sulfur. Diazo reagents allow synthesis of azoles of many types with two, three, and four heteroatoms. These heterocycles have found broad application in many fields such as organic electronics, functional materials, explosives, dyes, fluorophores, and especially medicine. This review aims to summarize all recent developments in this area covering all types of azoles available from diazocarbonyl and related compounds (oxazoles, thiazoles, imidazoles, pyrazoles, triazoles, tetrazoles, with the exception of 1,2,3-thiadiazoles), as well as to consider earlier useful methodologies not mentioned in other reviews.
Diazo azoles, namely diazo pyrazoles 1 and diazo imidazoles 4 , were employed for the synthesis of N-azolyl-1,2,4-triazoles 3 and 5 in a study reported by Sadchikova and co-workers [1]. Interestingly, when a primary or secondary amide moiety was present in the diazo heterocyclic substrate, the reaction gave azolotriazinones instead of triazoles.
Imidazole derivatives are widely used in medicinal chemistry. Agents based on imidazole moiety possess anticancer, antifungal, antibacterial, antiviral, anti-inflammatory, and other biological activities [8]. Another area of application of imidazoles is in organic light-emitting diodes (OLEDs) and semiconductors [9]. To date, many methods have been developed for the synthesis of imidazoles, including the classical Debus-Radziszewski imidazole synthesis and reaction of a-halo carbonyl compounds with amidines [10,11]. However, syntheses based on diazocarbonyl compounds have not yet become widespread. There are two main approaches to the preparation of imidazoles using diazocarbonyl compounds: Metal catalyzed insertion into the NH bond of ureas followed by cyclization with formation of 2-imidazolones (which can be easily converted to substituted imidazoles), and NH-insertion into amides followed by cyclization in the presence of amine or an ammonia source. In addition, there are also some more exotic syntheses making use of isocyanides, imines, and nitriles
Another example of gold-catalyzed reaction of vinyl diazo compounds for the synthesis of pyrazole derivatives was described in 2019 by Raj and Liu [12]. The procedure involving [5+4]-annulation between 2-alkynyl-1-carbonylbenzenes 22 and vinyl diazo ketones 23 afforded 4,5-dihydro-benzo[g]indazoles 24 in generally good yields and with high diastereoselectivity. These initial products can be further converted to aromatic pyrazoles . The possible reaction mechanism likely involves the goldcatalyzed formation of benzopyrilium cation followed by its [5+4]-cycloaddition with vinyldiazo ketone 23 to yield intermediate. The latter can be hydrolyzed to give intermediatewhich then undergoes a disrotatory 6_-electrocyclization with subsequent diastereoselective protonation leading to the observed pyrazoline 24(Scheme 7).
Conclusion
Most recently, great progress has been achieved in the synthesis of tetrazoles from various diazo compounds. However, it is obvious that the synthetic potential of diazo compounds in this area is far from its full disclosure. In addition, despite the extensive research, some mechanistic details are still not clear and need further investigation. Given the easy availability of diazo substrates, the described methodologies represent a valuable alternative to more conventional methods. As we have demonstrated in this review, diazocarbonyl and related compounds provide rapid and efficient access to a wide range of various azoles.
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