Organosulfur Chemistry. II. Use of Dimethyl Sulfoxide ; a Facile Synthesis of Cyclic Sulfides

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A versatile and short-reaction-time synthesis of twelve four-, five- and six-membered thiacy-cloalkanes (II_a-l) from the appropriate α, ω-dibromoalkanes (I_a-l) has been developed. Technical-grade dimethyl sulfoxide was proved to be by far the best for this cyclization. The pronounced effect for ring formation was recognized to be in order of five-membered ring (thiolanes) > six-membered ring (thianes) > four-membered ring (thietanes). Startling were 2-methylthiolane (II_f) and 2, 5-dimethylthiolane (II_g ; cis, trans mixture), both obtained in high yields although α-methyl-and α, α'-dimethyl substitution in general showing a remarkable retardation for cyclization. On the other hand, in both 3, 3-dimethylthietane (II_d) and 4, 4-dimethylthiane (II_l) cyclization was much more efficient than other counterparts in each series, which is referred to as the gem-dimethyl effect.