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

Abstract

The 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.

Reaction of β‐dimethylaminovinyl ketones with hydroxylamine: A simple and useful method for synthesis of 3‐ and 5‐substituted isoxazoles

“…Considering that the reaction of 1,1,1-trihalo-4-alkoxy-3-alken-2-ones with hydroxylamine hydrochloride is usually carried out in the presence of pyridine [18,19], we used pyridine in ethanol under reflux for 16 hours in the preliminary investigation. The result obtained for precursors with R = Ph, Cl-4-C 6 H 4 , thien-2-yl was a mixture of the 3-substituted-4,5-dihydroisoxazoles 5 and 5-substituted-isoxazoles 4.…”

Polyphosphate im marinen Phosphorkreislauf

“…The starting material, 1,1‐dichloro‐4‐methoxy‐3‐penten‐2‐one 1 , was synthesized from the reaction of 2‐methoxypropene with dichloroacetyl chloride, by methodologies developed in our laboratories [6, 20, 21]. The synthetic method used to obtain β‐enamino dichloromethyl ketones presented in this article was based on the solvent‐free reaction of 1,1‐dihalo‐4‐methoxy‐3‐penten‐2‐one with amines.…”

5-Halomethyl-5-Hydroxy-4,5-Dihydroisoxazoles: Synthesis and 13C, 17O,15N, 19F NMR Spectroscopy

“…Considering that the rate determination step of the reaction is the Michael type conjugated addition, the nucleophilic nitrogen atom of hydroxylamine attacks exclusively the -carbon atom of enone, while the oxygen atom attacks carbonyl carbon leading to 5-halomethyl-5-hydroxy-4,5-dihydroisoxazoles 9 regiospecifically [18][19][20]40,[43][44][45][46][47][48] (Scheme 10). The presence of a halomethyl group in the precursor is a determining factor in the regiochemistry of the reaction.…”

“…-Alkoxyvinyl halomethyl ketones derived from dihydrofuran and dihydropyran 33 reacted with hydroxylamine and provided a mixture of 5-halomethyl-5-hydroxy-4,5-dihydroisoxazoles 34 and 3-cyano-2-halomethyl-2-hydroxy-tetrahydrofuran or -tetrahydropyran 32 [20,45] (Scheme 12). The product ratio was mainly governed by the reaction temperature.…”

“…i: NH 2 OH HCl, Et 3 N, PrOH, BF 3 OEt 2 , reflux, 16 h Scheme 7. group of the hydroxyalkyl side chain, resulting in the closure of the ring, where the oxime group is easily dehydrated forming the cyano group [45].…”