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 the primary alcohol group of nopol to the aldehyde, followed by H/D exchange
and reduction back to alcohol, were unsuccessful because various oxidation procedures, including reaction with
N-chlorosuccinimide at 278 8C, gave instead a carboxylic acid having an oxygen at C-3. Nopol, labelled at C-11
with deuterium, was obtained through a Prins reaction of b-pinene with deuteriated paraformaldehyde. This
labelled nopol was converted into its toluene-p-sulfonate ester, and was solvolysed in acetic acid containing acetate
ion to give 8,8-dimethyltricyclo[4.2.1.03,7]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 this deep-seated
carbon skeletal rearrangement proceeds through the intermediate formation of a cyclobutane ring, followed by
shift of a methylene bridge to expand the original cyclobutane ring and then subsequent expansion of the new
cyclobutane ring. Calculations of heats of formation of possible ions involved in these shifts confirm the proposed
mechanism as the most likely pathway.Junta Nacional de Investigação Científica e Tecnológica.
Kuwait.
Eschenmoser Trust UK
