Heterosulfur atoms

The naming and numbering of each parent system follow current practice by Chemical Abstracts. To assist the reader, the number 1 position in the structural formula and the number position of each heterosulfur atom are shown. However, the molecular structure is oriented so as to emphasize the relationship to the structure of its benzolog rather than to conform with the rules of Chemical Abstracts. Each system wherein the parent compound has been synthesized and described is designated by an asterisk. Selected data on this parent are presented in Table III. Some key references to the thiophene system are listed in each case. 

The direct insertion of a sulfur atom into the skeleton of a precursor molecule to form a heterocyclic ring is known as sulfur bridging. The heterosulfur atom regularly arises from elemental sulfur or an inorganic sulfur compound such as H2S, Na2S, S02, or SOCl2. Sulfur bridging may involve simple addition, addition-elimination, or replacement of an atom, ion, or molecule. 

In the case of 3-(2 -thienylidene) camphor 243 chlorosulfonation, under similar conditions, gave the 5 -sulfonyl chloride (sulfonation adjacent to the electron-donating heterosulfur atom). 4-Benzylidenepinocamphorone 244 reacted with excess chlorosulfonic acid (six equivalents) at room temperature (1 week), followed by treatment with thionyl chloride-DMF catalyst, to give the /7-sulfonyl chloride, characterized by formation of sulfonamide deiivatives. 2-Thienylideneacetone 245, together with the benzylidene derivatives of ethyl methyl ketone 246 and diethyl ketone 247, by treatment with excess chlorosul-... 

Thiannulation is used here to designate the formation of a heterosulfur ring from an organosulfur precursor. It may result from the intermolecular condensation of two or more precursors, one bearing the requisite sulfur atom in an acyclic structure. Alternatively, it may involve an intramolecular cyclization. By contrast, sulfur bridging involves inorganic sulfur as the source of the heteroatom. 

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