of which contain 4n cyclic T electrons. The isothiazole 2 was obtained from 1 by a sulfur insertion-rearrangement reaction as shown in Scheme I. The ring opening to give the trans- dicyanoethylene intermediate 3l is assisted by resonance stabilization of the sulfide anion portion of the intermediate. This unusual reaction has now been extended to the synthesis of dicyano-1, 4-dithiino [2, 3-c; 6, 5-c'] diisothiazole 43 and 5-cyanoisothiazole dithiolate 7.* 3 ...