A novel reaction of 2-(arylamino)-1-(methylthio)-1-tosylethenes with hydrogen iodide leading to quinoline derivatives

The reaction of 2-(arylamino)-1-(methylthio)-1-tosylethenes (4) with hydrogen iodide in refluxing toluene gave 3-tosyl-2-(tosylmethyl)quinoline derivatives (6) in good yields. In this reaction, hydrogen iodide dose not only reductively removes the methylthio group of 4 to form an intermediary 1-(arylamino)-2-tosylethene (5), but also serves as a protic catalyst for the subsequent dimeric cyclization of 5 to lead to the quinoline derivatives (6).