INTRAMOLECULAR CATALYSIS IN ACETYLATION OF METHYL CHOLATE

The hydroxyl groups of methyl cholate decrease in reactivity toward acetic anhydride in the order 3 > 12 > 7 when they are present in compounds free of intramolecular influences. In methyl cholate, however, the 7-hydroxyl is acetylated in preference to the 12-hydroxyl as a result of three interactions: (1) deactivation of the 12-hydroxyl by the side chain, (2) enhancement of 7-hydroxyl reactivity by a 3-acetoxy group, and (3) enhancement of 7-hydroxyl reactivity by the 12-hydroxyl. Preferential acetylation at the 7-hydroxyl occurs also in the absence of a 3-acetoxy group, as in methyl 3α,7α-dihydroxycholanate. © 1969, American Chemical Society. All rights reserved.