4,5位置換イソオキサゾール類の合成および開裂反応に関する研究 (第5報)

フラン核を有するイソオキサゾール体とα-シアノケトン体の反応について

抄録

Syntheses and cleavage reaction were attempted with 4, 5-disubstituted isoxazoles with a furan ring. In order to obtain the starting α-formyl ketone compound, usual formylation with ethyl formate was carried out on deoxyfuroin (I), acetyl-furan (II), furfuryl benzyl ketone (III), and furyl benzyl ketone (IV). (I) failed to undergo this reaction, the formyl compounds of (II) and (III) were so labile that they easily underwent resinification, and only the α-formylbenzyl furyl ketone (IV′), m.p. 100-101°, was sufficiently stable. (IV′) colored reddish violet with Fe³⁺ in 2γ/0.05cc. concentration and this color is an iron complex salt (V) of m.p. 179-180°, with a molar ratio of (IV′) to iron of 3:1.
Reaction of (IV′) with equivalent of hydroxylamine hydrochloride in ethanol afforded 4-phenyl-5-furylisoxazole (VI), b. p₃ 145-146°, and its reaction with sodium ethoxide in ethanol solution resulted in cleavage to furoyl-phenylacetonitrile (VII), m.p. 89-89.5°. On heating with 25% sodium hydroxide at 100° for 30 minutes, (VII) was decomposed into 2-furoic acid and benzyl cyanide. Oxidative decomposition of (VII) in dilute sodium hydroxide with hydrogen peroxide resulted in preferential cleavage of the furan ring and benzoic acid was obtained as one of the acid components but not 2-furoic acid. Amidation of (VII) with 95% sulfuric acid gave 2-furoyl-2-phenylacetamide (VIII), m.p. 184-185°, whose hydrolysis with dilute sulfuric acid gave the starting compound (IV).
It was revealed from these experimental results that the series of reactions used for syntheses and cleavage for 4, 5-substituted isoxazoles with aromatic ring carried out in the past is also applicable for the present comparatively stable starting compound, the α-formyl ketone compound with a furan ring.