The Diels-Alder cycloadditions of the acyclic and cyclic vinylketene dithloacetals 4 prepared from the corresponding oxoketene dithioacetals 2 either by 1, 2-addition of methylmagnesium iodide and subsequent dehydration or by Wlttig reaction, were studied. Thus 4a-e and 4h-i underwent facile [4+ 2] cycloaddition with maleic anhydride followed by elimination of methylmercaptan and subsequent aromatization through dehydrogenation ...
