Zinc Chloride Mediated Synthesis of 3H‐Oxazol‐2‐one and Pyrrolo‐oxazin‐1‐one from Ynamide

Abstract

A simple zinc chloride mediated cyclization of ynamidyl N‐carbamates or 2‐ynamidyl‐(hetero)arylcarboxylates is achieved under mild reaction conditions, leading to the synthesis of useful heterocyclic scaffolds, 3H‐oxazol‐2‐ones and pyrrolo‐oxazin‐1‐ones, with good yields.

Diorganyl Diselenides and Iron(III) Chloride Drive the Regio- and Stereoselectivity in the Selenation of Ynamides

“…At this point in our studies, even knowing that alkynyl carbamates were cyclized to oxazolones using transition-metal catalysts, we are pleased with the result obtained in Scheme , eq 2, because the synthesis of oxazolones with concomitant functionalization of the 4-position is rare . Oxazolones are structural subunits found in several numbers of synthetic structures with various biological activities .…”

A Ag2CO3/TFA-catalyzed intramolecular annulation approach to imidazo[1,2-c][1,3]oxazin-5-one derivatives

“…In order to prepare a library of new imidazo[1,2- c ][1,3]oxazin-5-one heterocycles, N -Boc-4-bromo-5-methyl-2-phenylethynylimidazole 1a was studied as a model substrate and subjected to some annulation process conditions which have been already described in the literature. 25,37,46,49,50,57–64 Compound 1a , which is a suitable substrate for undergoing intramolecular annulation, was prepared following our recent procedure involving the regioselective Sonogashira cross coupling reaction of N -Boc-2,5-dibromo-4-methylimidazole. 48 Initially, the zinc catalyst (ZnCl 2 ) was used in dichloromethane at 40 °C but it was found to be totally inert since the starting material was completely recovered after 48 h (Table 1, entry 1).…”

Palladium-Catalyzed Cascade 5-endo-dig Cyclization of Ynamides to Form 4-Alkynyloxazolones

“…Nitrogen- and oxygen-containing heterocycles are undoubtedly among the most studied classes of compounds and, consequently, the most cited in the literature. , The high citation of nitrogen- and oxygen-containing heterocycles in the scientific literature is explained by their wide application in medicine, pharmacology, materials science, natural products, and as substrates for new transformations. , Therefore, several methodologies for synthesizing N -( O )-heterocycles have been developed. − Among them, metal-catalyzed intramolecular and intermolecular cyclization reactions are frequently used because of their efficiency, high selectivity, and tolerance to a wide range of functional groups. − In these reactions, alkenes or alkynes have been used as substrates, in which the transition metal activates the carbon–carbon multiple bonds, and a nitrogen or oxygen nucleophile, located in a suitable position, promotes the nucleophilic attack to carbon–carbon, leading to the cyclization process. , Lately, the environmental issues and costs, both from the academic and industrial areas, have required new advances and challenges for transition-metal-catalyzed and metal-free cyclization reactions. − Thus, the transition metal-catalyzed cascade reactions are a rapidly growing research area of cyclization reactions because of the atom efficiency, saving time, energy, and money, meeting requirements of the modern and environmentally benign and sustainable chemical processes. − This paper deals with our investigation concerning the selective synthesis of 4-alkynyloxazolones 2 from ynamides 1 , − readily available starting materials, through the formation of carbon–oxygen and carbon–carbon bonds in a cascade transformation (Scheme , eq b). The oxazolone is a central core present in many compounds, having valuable properties for biological activity and intermediate for the synthesis of more complex structures. − However, despite the great importance of substituted oxazolones, very few straightforward syntheses of 4-alkynyloxazolones have been studied. − Zhu and co-workers described the synthesis of 4-alkynyloxazolone using the iodocyclization of ynamide combined with the Sonogash...…”