Transformations of 2-(phenylethynyl)isocamphanol under acid catalysis

Abstract

2-exo-(Phenylethynyl)isocamphanol prepared from lithium phenylacetylide and isocamphanone suffered under conditions of Ritter reaction a conversion predominantly into a mixture of 2-(benzoylmethylene)isocamphane and 2-(benzoylmethylene)bornane that formed as a result of rearrangements of the initial acetylene alcohol by Meyer-Schuster and partially by Wagner-Meerwein. The enones ratio depends on the reaction conditions and varies from 5:4 to 1:3. The product of nucleophilic substitution, N-(4-benzoylmethyl-2-isobornyl)acetamide, formed in a yield no higher than 10%. Analogous rearrangements occurred at treating 2-phenylethynylisocamphanol with formic acid; here the mixture of the above enones formed in a ratio 1:2. The initial acetylene alcohol treated with Beckmann mixture gave rise to the same enones in a ratio 1:1, and the target 2-endo-(phenylethynyl)isocamphanol acetate formed as minor product (∼15%). The individual α,β-unsaturated ketones under the Ritter reaction conditions were selectively converted into N-(4-benzoylmethyl-2-isobornyl)acetamide.