Reaction of 1-adamantyl cation with carbon monoxide in the presence of adamantane and trifluoromethanesulfonic acid: a convenient route to 3,4-homoadamantanediol

Abstract

The carbonylation of the l-adamantyl cation with carbon monoxide in carbon tetrachloride at atmospheric pressure in the presence of trifluo-romethanesulfonic acid (triflic acid) and adamantane affords 3-hydroxy-4-homoadamantyl l-adamantanecarboxylate ( 2) in 70% yield under appropriate conditions. Among various l-adamantyl cation precursors tested, l-adamantyl trifluoromethanesulfonate (triflate) and methanesulfonate (mesylate) have given the best, comparable results. As to the acid catalyst, fluorosulfonic acid is less effective than triflic acid, and 100% sulfuric acid and methanesulfonic acid are completely ineffective to produce 2. It is recommended to use five mol each of triflic acid and adamantane per mol of l-adamantyl mesylate or triflate. This reaction proceeds via the addition of the l-adamantanecarbonyl cation to l-adamantanecarbaldehyde, a transient intermediate, followed by the Wagner-Meerwein rearrangement. The hydroxy ester 2 is easily converted into 3,4-homoadamantanediol which is a promising starting material for 3,4-bifunctional homoadamantane derivatives.