Reactions of 3-(polyfluoroacyl)chromones with hydroxylamine. The first synthesis of 3-cyano-2-(polyfluoroalkyl)chromones

摘要

Reaction of 3-(polyfluoroacyl)chromones with hydroxylamine proceeds via nucleophilic 1,4-addition followed by opening of the pyrone ring and subsequent cyclization to 4-(polyfluoroalkyl)-4H-chromeno[3,4-d]isoxazol-4-ols in good yields. On treatment with trifluoroacetic acid, the isoxazole ring of this annulated heterocyclic system opens to give 3-eyano-2-(polyfluoroalkyl)chromones. Reaction F of 3-(polyfluoi-oacyl)chromones with hydroxylamine hydrochloride occurs only at the carbonyl carbon atom connected to the R group to give the corresponding oximes in low yields. (c) 2006 Elsevier Ltd. All rights reserved.