Haloacetylated enol ethers. 5 [5]. Heterocyclic ring closure reactions of β‐alkoxyvinyl dichloromethyl ketones with hydroxylamine

Abstract

AbstractThe β‐alkoxyvinyl dichloromethyl ketones 1a‐d are cyclocondensed with hydroxylamine hydrochloride in pyridine to afford the 5‐hydroxy‐5‐dichloromethyl‐4,5‐dihydroisoxazoles 2a‐d in good yield. The cyclo‐condensation of compound 1c gave, together with 2c, 3‐cyano‐2‐hydroxy‐2‐dichloromethyltetrahydrofuran 5c. The dehydratation of compounds 2a,b, derived from acyclic enol ethers, with concentrated sulfuric acid at 30°, led the corresponding 5‐dichloromethylisoxazoles 3a,b. The dehydratation of compounds 2c,d, derived from cyclic enol ethers, with concentrated sulfuric acid at 30°, led the bicyclic 4,5‐dihydroisoxazoles 4c,d, and at 55°, a competitive rearrangement reaction gives the 3‐cyano‐2‐hydroxy‐2‐dichloromethyl‐2H‐pyran 5d.