Rings containing Nitrogen and Oxygen

Nitrogen- and Oxygen-containing Rings - a-Hydroxy-hydroxamic acids react with carbonyl di-imidazole to give, after carbon dioxide extrusion either spontaneously or on heating, the substituted oxazetidin-3-ones (69), and 1,3-di-imines react with hydroxylamine in pyridine at room temperature to give the dihydroisoxazoles (70). 56 

Cycloaddition reactions as an approach to nitrogen- and oxygen-containing heterocycles have dominated the literature this year and are the topic of the remainder of this section. The intramolecular cycloaddition of aryl oxaziridines to give fused isoxazolidines (71) proceeds in good yield, presumably via a nitrone intermediate. On the other hand the oxime (72) undergoes an intramolecular cycloaddition to give the isoxazolidine (73) and can either be 

Michael type reaction. Chlorosulphonyl isocyanate adds to epoxides to generate the carbon dioxide inserted oxazolidines (74) or dioxalones (75) depending on the substitution pattern of the epoxide. 

Weinreb et al. have systematically explored the intramolecular Diels-Alder reaction of N-acyl-imines generated from the bisamides (79) to extend the usefulness of this little studied reaction. 

boron trifluoride catalysed intramolecular cycloaddition of (79) gives stereospecifically the dihydroxazines (80) in good yield (58-89%), 62 

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Nitrogen- and Oxygen-containing Rings.- Five-membered Rings. 

Five-membered Nitrogen- and Oxygen-containing Rings. Huisgen et al. have generated benzonitrile-4-nitroben lide (102) in small equilibrium concentrations. This is the first representative of a class of nitrile ylides and... 

Six-membered Nitrogen- and Oxygen-containing Rings. The cycloaddition between aroyl isothiocyanates and NN-disubstituted hydrazones, especially of cyclanones, gives unstable derivatives of 1,3,5-oxadiazine (147). ... 

Electrophilic cyclizations are useful for closure of a variety of oxygen-, nitrogen-, and sulfur-containing rings. The product structure depends on the ring size and the exo-endo selectivity. The most common cases are formation of five- and six-membered... 

A variety of pathways give rise to the nitrogen-and oxygen-containing heterocyclic rings of nature. 

A particularly useful general method for the synthesis of saturated nitrogen- and oxygen-containing partially unsaturated heterocycles, from 5-membered to medium ring-sized, is the Grubbs olefin metathesis applied, for example, to acyclic diaUcenyl-amines, as illustrated by syntheses of a dihydropyrrole and a tetrahydropyridine. ... 

Chiral 10 to 12-membered nitrogen and oxygen heterocycles, fused to isoxazo-line rings have been prepared with high regio- and stereoselectivity by INOCs of tethered N- and O-allyl carbohydrate derivatives. The use of a -Y-Ar-CH2 tether, containing a 1,2-disubstituted aromatic ring between the heteroatom attached to... 

Abstract Heterocyclic compounds containing atoms of the elements snch as nitrogen, snUhr and oxygen as ring members are commonly nsed in varions fields of indnstiy as analytical reagents, ligands, dyestuffs, pharmaceutical substances and bioindicators. 

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