Sulfur compounds four-membered rings

Formation of anionic rr-adducts from heteroaromatic compounds, 34, 305 Four-membered rings containing one sulfur atom, 35, 199... 

We can learn from this compound that sulfur has much less objection to four-membered rings than do oxygen or carbon. We have seen from the structure of sulfur itself (Sg) that it likes eight-membered rings too. Rings of almost any size are acceptable to sulfur as bond angles matter less to second-row elements that are not generally... 

The intramolecular participation of the sulfur in reactions of 26 involves the formation of a three-membered ring in the intermediate. A study of the analogous reaction of nitrogen compounds to form cyclic amines (equation 8.26) led to the conclusion that Ihree-membered ring formation occurs with a greater rate constant than does formation of a four-membered ring (Table 8.6). The rate constant for formation of five-membered rings is fastest of all of the compoimds studied, however. ... 

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