Studies on the Terpenoids and Related Alicyclic Compounds. XXXIII. Acid-Catalyzed Allylic Rearrangement of 1-Hydroxy-2-en-and 3-Hydroxy-1-en-5α-cholestanes

抄録

The reaction mechanism and the stereochemistry of an acid-catalyzed allylic rearrangement of four allylic alcohols of 5α-cholestane, the 3-hydroxy-1-enes (5 and 6) and the 1-hydroxy-2-enes (7 and 8), were investigated. The allylic alcohols were heated in dioxane containing a small amount of 1N H₂SO₄. After the equilibration of the reaction, the products ratio of the four allylic alcohols, 5 : 6 : 7 : 8, was found to be 25 : 20 : 52 : 3, regardless of the stereochemistry of the starting materials. The mechanism of the allylic rearrangement is of S_N1 type. The products ratio could be explained in terms of the relative stabilities of the C-1 and C-3 carbocations in the intermediates and the thermodynamic stability of each allylic alcohol.