The mechanism of formation of 8,8-dimethyl[4.2.1.0(3,7)]nonan-6-yl acetate(fortesyl acetate) during acetolysis of nopyl toluene-p-sulfonate

Attempts to prepare 2-(2-hydroxyethyl)-6,6-dimethylbicyclo[3.1.1]hept-2-ene (nopol; 1) labelled with deuterium at C-10 by a process of oxidation of th e primary alcohol group of nopol to the aldehyde, followed by HID exchange and reduction back to alcohol, were unsuccessful because various oxidation procedures, including reaction with N-chlorosuccinimide at -78 degrees C, g ave instead a carboxylic acid having an oxygen at C-3. Nopol, labelled at C -ll with deuterium, was obtained through a Prins reaction of P-pinene with deuteriated paraformaldehyde. This labelled nopol was converted into its to luene-p-sulfonate ester, and was solvolysed in acetic acid containing aceta te ion to give 8,8-dimethyltricyclo[4.2.1.0(3,7)]nonan-6-yl acetate, which: is an earlier reported novel fused ring system (fortesyl acetate;2 acetate) . The position of the label in the product showed that the mechanism of thi s deep-seated carbon skeletal rearrangement proceeds through the Intermedia te formation of a cyclobutane ring, followed by shift of a methylene bridge to expand the original cyclobutane ring and then subsequent expansion of t he new cyclobutane ring. Calculations of heats of formation of possible ion s involved in these shifts confirm the proposed mechanism as the most likel y pathway.