Reaction of cyclic ketenethioacetal, 3-(methylthio) thiapyrano [3, 4-b] indol-1-one (Ia, b) and active methylenes was carried out and the corresponding products (IIIa-e) with the methylthio group substituted were obtained. Reaction of 4-(methylthio)-pyrano [3, 4-b] indol-2-one with active methylenes also afforded the corresponding substituted products (IVa-c).
