Synthesis, Property, and Reactivity of Novel π-Electron System Linked with Hetero Atoms

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3,4-Bis(methoxycarbonyl)-1, 2-dithiete (1), 3,4,7,8-tetra(methoxycarbonyl)-1,2,5,6-tetrathiocin (2), and (Z,Z,Z,Z)-3,4,7,8,11,12,15,16-octa(methoxycarbonyl)-1,2,5,6,9.10,13,14-octathiacyclohexadeca-3,7,11,15-tetrraene (3) were synthesized by oxidation of corresponding titanocene dithiolene complex with sulfuryl chloride, and the crystal structures of 1 and 2 were characterized by X-ray crystallographic analysis which revealed planar and twist geometries, respectively. Hydrogen-substituted tetrathiocim 4 and sixteen-membered cyclic compound 5 were also obtained by oxidation of the corresponding dithiolate or dithiolene complex. 1,2-Dithiete 1 underwent tetramerization selectively to give sixteen-membered cyclic compound 3 even at room temperature. Ring conversion reactions also proceeded among the four-, eight-, and sixteen-membered unsaturated cyclic compounds possessing disulfide linkage under various conditions, such as in polar solvent or in the presence of silica-gel. The ring-size … More selectivity of these ring conversion reactions was studied using ab initio molecular orbital calculations. Reactions of 1,2-dithiete 1 with various alkenes or alkynes formed 2,3-dihydro-1,4-dithiins of thiophenes, respectively. The reactions with alkenes were stereospecific, which indicates the concerted reaction between 1,2-dithione 6, valence isomer of the 1,2-dithiete, and the dienophiles. Theoretical study confirmed the reactions of & with alkenes and alkynes are reverse electron demand hetero Diels-Alder reaction. The MO calculations showed the 1,2-dithiete 1 was 5.8 kcal molィイD1-1ィエD1 more stable than the corresponding ehane-1, 2-dithione 6, and the tautomerizaion energy between the 1,2-dithiete and the ethane-1, 2-dithione was also calculated to be 28.5 kcal molィイD1-1ィエD1 from the 1,2-dithiete, which suggests the tautomerization from 1,2-dithiete 1 to ethane-1, 2-dithioe 6 is possible at least at high temperature. Reaction of 1,2,5,6-tetrathiocim 2 or sixteen-membered cyclic compound 3 with ethyl vinyl ether also formed the 2,3-dihydro-1,4-dithiin derivative, which is the same compound obtained by the reaction of 1,2-dithiete 1 with the ether. Tetrathiocin 2 and sixteen-membered cyclic compound 3 also reacted with diphenylacetylene to give the thiophene derivative. Less