Thiine-2-thione

In the thermal reaction of fluorinated fullerene (C60F18) with tetrathiafulvalene (180, TTF), a thiin-2-thione adduct 181 was isolated as a minor product. This is believed to form by a cycloaddition of thiin-2-thione 182 (formed by elimination of CS2 from TTF) with the initial adduct (C60F16-TTF) of C60F18 with TTF (Scheme 38) [113]. A convenient (although low-yield) method for the preparation of 6-arylthiin-2-thione 183 has been reported (Eq. 36) [114]. 

The reaction of disulfide 184 with electron-deficient acetylenes 185 yields 2,3-disubstitued-4-(diethylamino)thiin-2-thiones 186 in moderate yields (Scheme 39) [115]. Syntheses of fused thiin-2-thione derivatives, 187 [91], 188 [116], 189 [117], and 190 [118] have been reported. 

As may be seen, the dominant feature of much of the chemistry of thiins is the tendency to form maximally conjugated ring systems such as pyrones or thiones, and alkylidene or... 

Pyran 200 (R1 = R2 = H) exists only as its acyclic valence tautomer but 5-acetyl-2,2,6-trimethylpyran 200 (R Me, R2 = Ac) is in equilibrium with only -35% of the valence tautomer 201 (R =Me, R2 = Ac) at 30 °C. The equilibrium of the bicyclic derivatives 202 with the ketone isomers 203 is influenced by solvent and temperature. In tetrachloroethene only 9% of the open-chain form is present at 30 °C but this rises to 40% at 113 °C <1981T1571>. Valence tautomerism of 2/7-pyran derivatives is the basis of some commercial photochromic materials. Similar properties are shown by 2/7-thiin derivatives such as the photochromic compound 204, which forms the thione 205 upon irradiation. 

The condensation of aldehydes with thiocyanoacetic esters, catalysed by potassium fluoride or potassium carbonate, gave as minor products yV-carbamoyl-2-imino-5-alkyl(or aryl)-l, 3-oxathiolan-4-carboxylic esters, in which the 4,5-c/j-isomers predominated according to n.m.r. spectroscopy. l,3-Oxathiolan-2-thione was converted into dimethyl 1,3-dithiol-2-one-4,5-dicarboxylate and ethylene on treatment with dimethyl acetylene-dicarboxylate, and the transformation of methyl 2-methoxycarbonyl-methyl-1,3-oxathiolan-2-carboxylate into dimethyl-5,6-dihydro-l, 4-oxa-thiin-2,3-dicarboxylate by chlorination at low temperatures found analogy in the reactions of 2,2-dialkyl-l,3-oxathiolans. Thiomethoxymethyl hexachloroantimonate reacted with potassium t-butoxide to give mainly 3,5,5-trimethyl-l,3-oxathiolanium hexachloroantimonate the mechanism of this remarkable reaction was not settled. ... 

---