H ünig's base and S 2 Cl 2 give the fused 1,4-thiazines 1 and (in the presence of formic acid) 2 and 3, each of which readily extrudes sulfur, selectively and quantitatively, to give the fused pyrroles 4, 5 and 6 respectively; at higher temperatures H ünig's base and S 2 Cl 2 can be converted into the pyrroles in one pot, and the cycloadducts 8 and 10 are thus readily available in two steps.

The reaction of N,N-diisopropylethylamine (Hünig's base) and disulfur dichloride in 1,2-dichloroethane, in the presence of DABCO, gives 4-ethylbis[1,2]dithiolo[5,4-b][4‘,5‘-e][1,4]thiazine-3,5-dithione (1), or, by addition of oxygen donors, the 3-oxo-5-thione 2 or 3,5-dione 3 derivatives are selectively obtained. When the first reaction is performed in boiling chlorobenzene, 4-ethylbis[1,2]dithiolo[4,5-b][5‘,4‘-d]pyrrole-3,5-dithione (4) is obtained by sulfur extrusion from 1, and in the presence of oxygen donors, the 3-oxo-5-thione 5 or 3,5-dione 6 derivatives are selectively obtained. Some interconversions of compounds 1−6 are described, and a coherent set of reaction pathways for the formation of all six products is proposed. X-ray diffraction shows that the new bis-dithiolothiazine ring system of 1−3 is folded out of planarity about the thiazine N−S vector, with the N-ethyl group folded back over the thiazine ring in a scorpion-like conformation. The new bis-dithiolopyrrole ring system of 4−6 is planar and extensively delocalized.

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The Ugi four-component condensation between cycloalkanones, isocyanides, and ammonium formate affords N-substituted 1-formylamino-1-cycloalkanecarboxamides 1 which are dehydrated to give the corresponding isocyanides 2. Compounds 2 are cyclized with arylsulfenyl thiocyanates to 1,3-diazaspiro-2-thiones 4 and 5. A series of 1,3-diazaspiro [4,5]dec-1-en-4-ones 7 is prepared by cyclizing 2c -1 with butyllithium.

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A convenient synthesis of the title compounds by means of the Ugi four-component condensation (Ugi 4-CC) is reported. The reaction between acetaldehyde azine (3a), 2-benzoylbenzoic acid (4), and cyclohexyl isocyanide (5) spontaneously afforded N-cyclohexyl 2-(1,2-dihydro-1-oxo-4-phenylphthalazin-2-yl)propionamide (1a) upon loss of acetaldehyde from the intermediate Ugi 4-CC adduct 6a. Starting from the less reactive azines 3c-f arising from ketones, the Ugi 4-CC adducts 6c-f did not spontaneously cyclize, whereas phenylacetaldehyde azine (3b) afforded a mixture of the Ugi 4-CC adduct 6b and cyclized product 1b. In all of the cases, the adducts 6b-f were easily cyclized to 1b-f in acidic medium.