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The reaction of the organozinc reagent prepared from methylene iodide and zinc‐copper couple with substituted unsaturated compounds has proved to be a versatile and convenient method for the synthesis of cyclopropanes. The synthesis is stereospecific with regard to the stereochemistry of the unsaturated compound and is usually free from serious side reactions; it can be carried out under mild conditions in diethyl and affords cyclopropanes often in good yields. This method can be easily adapted to large‐scale preparations. Two useful variations of the cyclopropanation reaction have appeared which involve the same or a similar organozinc intermediate: (1) diazomethane reacts with iodide in ether to form a reagent which converts unsaturated compounds to cyclopropanes; (2) methlyene iodide and diethyl zinc react in ether in the presence of unsaturated compounds to cyclopropanes. Processes are known in which a divalent carbon fragment adds to carbon‐carbon double bonds either as a free carbene or as an organometallic complex.

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The synthesis of l,4-dithiino [2,3-c;6,5-c1diisothiazole-3,7-dicarbonitrile and isothiazole[3,4-/][l,2,3,4,5]pentathiepine-8-carbonitrile by a sulfur insertion-rearrangement reaction of l,4-dithiin-2,3,5,6-tetracarbonitrile is described. The sulfur insertion-rearrangement of disodium dimercaptomaleonitrile gives 5-cyanoisothiazoledithiolate. The physical and chemical properties of these heterocyclic systems are reported together with a qualitative molecular orbital treatment which provides the key to understanding their properties.Thiacyanocarbons1 are an interesting class of compounds in that they can be prepared entirely from inorganic sources, namely, sodium cyanide, carbon disulfide, and sulfur. Their versatility as intermediates for the synthesis of novel heterocycles has been demonstrated.1,2 Heterocycles reported previously1 include stable tetracyano-1,4dithiin (1) and tricyano-1,4-dithiino[c]isothiazole (2), both of which contain 4n cyclic 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 frans-dicyanoethylene intermediate 31 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-l,4-dithiino[2,3-c;6,5c'Jdiisothiazole 43 and 5-cyanoisothiazole dithiolate 7.4,5 We report here the synthesis and properties of these molecules together with a qualitative molecular orbital (MO) treatment which provides the key to understanding their properties. SynthesisThe reaction of 1 with sulfur in the presence of a basic catalyst, such as sodium iodide or tertiary amines, affords 4 as a pale yellow crystalline solid, mp 286-289 °C. The isothiazole 2 is most probably an intermediate to 4 (Scheme II). Application of the sulfur insertion-rearrangement mechanism discussed above predicts that the negatively charged sulfur nucleophile adds to 2 followed by ring opening to give preferentially 5a which is better stabilized than the alternative intermediate 5b. The former can cyclize to give 4. The trans geometry of 4 has been unambiguously established by three-dimensional, singlecrystal, X-ray analyses.6 We find no evidence for the presence of the cis isomer which would have been derived from 5b. Compound 4 is prepared more conveniently in the laboratory from disodium dimercaptomaleonitrile (6, Bahr's salt7) via 4,5-clicyano-l,3-dithia-2-oxocyclopentene.8Polysulfide, generated from sulfur and a base, is again a useful catalyst for conversion to 4. $ Bahr's salt, 6,7 itself undergoes a formal sulfur insertion-rearrangement reaction to give the isothiazole 7 (Scheme III).9 The reaction proceeds slowly in ethanol f Contribution No. 2652.

Aus dem Tetracyan‐dithiin (I) entstehen mit Sulfiden in Gegenwart von NaI die kondensierten Cyan‐isothiazole (II) und (III).