Oxidative Degradation of Arylfuro-1,2-Oxazoles to Arylnitriles by Potassium Permanganate

Abstract

Arylfuroisoxazolines are oxidatively degraded to arylnitriles by treatment with a mixture of potassium permanganate and sodium acetate in dry dioxane.The ease of isoxazoline preparation through 1,3-dipolar cycloaddition reactions and the lability of the N-0 bond have made this heterocyclic system a versatile intermediate in organic synthesis. 1 The isoxazolines are reductively cleaved to ß-hydroxy ketones 2 or to aminoalcohols. 2,3The latter methodology has been successfully applied to the synthesis of natural products. 3,4 ß-Hydroxy ketones have also been prepared by peracid oxidation of 2-isoxazolines, 5 whereas oxidation of 4-isoxazolines leads to α,β-unsaturated'carbonyl compounds. 6 Isoxazoles may be prepared from 2-isoxazolines under oxidative conditions. 7 " 9 However, few examples of dehydrogenation by KMn0 4 have been reported. 9Imidazolines can be dehydrogenated to imidazoles by treatment with KMn0 4 and NaOAc in dry dioxane. 10 By analogy, it was thought that isoxazoles could be obtained from isoxazolines.Accordingly, 5-acetylisoxazolines la-d were dissolved in dry dioxane and treated with KMn0 4 (6 molar equivalents) and NaOAc (3 molar equivalents). The mixtures were stirred at 90 °C for 24 hours to give isoxazoles 2a-d albeit in low yields." 209 Brought to you by | Purdue University Libraries

Some nucleophilic substitutions in 2‐cyano‐3‐nitroimidazo[1,2‐a]pyridine

“…The latter mode, the nucleophilic adition, is shown in the condensation of 2amino-5-nitrobenzonitrile with 4-nitrobenzonitrile giving 2-(4-nitrophenyl)-4-amino-6-nitroquinazoline [11]. The cine-Scheme I As shown in Scheme 1, 3-nitroimidazo [1,2-a]pyridine-2carbonitrile (3) was prepared from ethyl 3-nitroimidazo[1,2-a]pyridine-2-carboxylate (1) [13] by ammonolysis with aqueous ammonia to give carboxamide 2 [14], followed by dehydration of the latter with phosphoryl oxychloride. The 3-nitro-2-carbonitrile 3 was then subjected to nucleophilic substitution reactions with guanidine in n-butanol.…”