Studies on Conformation and Reactivity. VI. The Reduction Reaction of Cholesta-3,5-dieno [3,4-b] oxathiane with Lithium in Liquid Ammonia. The Characterization of Unique Ultraviolet Absorption of the 3,5-Dieno [3,4-b] oxathiano System

In connection with characterization of unique ultraviolet absorptions at around 223 and 270 mμ of the 3, 5-dieno [3, 4-b] oxathiano system in the steroid nucleus, cholesta-3, 5-dieno [3, 4-b] oxathiane was reduced with lithium in liquid ammonia to give cholest-3-eno [3, 4-b] oxathiane accompanied by 4α-(β-hydroxyethylthio)-cholest-5-ene, bis (cholest-4-en-4-yl) disulfide, and a mixture of cholest-4-ene and -5-ene. The 3-eno [3, 4-b] oxathiano system thus obtained gave in its ultraviolet spectrum an absorption at 227 mμ. It led to a conclusion that the local conjugation of non-bonding p-electrons of oxygen and sulfur atoms and π electrons of 3-C and 4-C atoms in the conformationally rather fixed 3-eno [3, 4-b] oxathiano system affords a unique ultraviolet absorption in a shorter wave length region than 230 mμ. Origin of characteristic ultraviolet absorptions of the 3, 5-dieno [3, 4-b] dithiano system was analogously deduced.