6‐Polyfluoroacyl‐ and 6‐Trichloroacetylnorkhellins: Synthesis and Reaction with Aromatic Amines.

Abstract

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Synthesis and Transformation of Halochromones

“…Although in some cases this transformation results in low yields, the availability of the starting materials and the easy reaction and purification procedures are the great advantages of this approach. This general method was also extended to furanochromone derivatives [112].…”

“…Reaction of 3-R F CO-chromones 197 with amines [110,112,202,203] (aliphatic and aromatic amines, the latter bearing electron-donating or electron-withdrawing groups) generally proceed via a nucleophilic 1,4-addition mechanism with concomitant opening of the pyrone ring and subsequent intramolecular cyclization of the intermediate at the COR F group leading to aminomethylene-2-hydroxy-2-R F -chromanones 198 (Scheme 62). The hydrogen bond between the pyranone carbonyl oxygen and the hydrogen of the NH group of chromanones 198 is an effective driving force to explain their formation, but the presence of the R F group which also stabilizes the cyclic hemiketal form and makes the dehydration step difficult must also be considered.…”