HALOACETYLATED ENOL ETHERS .5. HETEROCYCLIC RING-CLOSURE REACTIONS OF BETA-ALKOXYVINYL DICHLOROMETHYL KETONES WITH HYDROXYLAMINE

The beta-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-dichloromethyltetrahy 5c. The dehydratation of compounds 2a,b, derived from acyclic enol ethers, with concentrated sulfuric acid at 30 degrees, led the corresponding 5-dichloromethylisoxazoles 3a,b. The dehydratation of compounds 2c,d, derived from cyclic enol ethers, with concentrated sulfuric acid at 300, led the bicyclic 4,5-dihydroisoxazoles 4c,d, and at 55 degrees, a competitive rearrangement reaction gives the 3-cyano-2-hydroxy-2-dichloromethyl-2H-pyran 5d.