Development of Environmentally Benign Methods Towards the Synthesis of anti-2,3-dihydro-1,2,3-trisubstituted-1H-naphth[1,2-e][1,3]oxazines Using Brønsted Acidic Catalysts

Abstract

This report has described three environmentally acceptable Bronsted acidic catalytic systems (p-toluene sulfonic acid, sulfamic acid and 1,3-disulfoimidazolium trifluoroacetate [DSIM][CF3COO] ionic liquid) for the preparation of complex library of anti-diastereomer of 2,3-dihydro-1,2,3-trisubstituted-1H-naphth [1,2-e][1,3]oxazines 4 from the three components reaction of 2-naphthol, p-substituted aromatic aldehydes and primary amines in 25 % aqueous ethanol at room temperature or in neat conditions at 80 °C. The reactions utilized 15 mol% of the two conventional acids to produce 82–97 % of naphthoxazines during 10–30 min. The same reactions could also be performed satisfactorily within 8–20 min employing 10 mol% of task specific acidic 1,3-disulfoimidazolium trifluoroacetate [DSIM][CF3COO] as catalyst. The three catalysts were recycled for four runs in aqueous ethanol with excellent catalytic activity.