Study On The Synthesis Of Oxazoles By β - Hydroxyl Esters By Trifluoromethanesulfonic Acid

Isoxazole and oxazole motifs make up the core structures of a wide range of natural products and synthetic molecules with important bioactivities. In particular,some pharmaceutical drugs are based on isoxazole and oxazoles units. Additionally,functionalized isoxazoles and oxazoles are widely used as key building blocks in the preparation of natural products and related structures. Their diverse biological activities and synthetic utilities have stimulated substantial interest in constructing the skeletons of such heterocycles. In this paper,we studied the synthesis of isoxazole and oxazole from β-oximyl amide accelerated by triflic anhydride（Tf₂O）.1. A facile and efficient synthesis of fully substituted 5-aminoisoxazoles was developed from α-ethylidene β-oximyl amides in the presence of Tf₂O in N,N-dimethylformamide（DMF） under very mild conditions, which involves sequential ring-opening and intramolecular cyclization reactions.2. One-pot synthesis of 5-iminooxazolines from β-oximyl amides mediated by Tf₂O in dichloromethane at room temperature is developed, and a mechanism involving tandem Beckmann rearrangement and intramolecular cyclization reactions is proposed.