Rearrangements of pinane derivatives. Part III. Solvolysis of the 2-pinanyl p-nitrobenzoates

Methanolysis of the 2-pinanyl p-nitrobenzoates in the presence of base gives a mixture of products including both cis- and trans-methyl 2-pinanyl ethers from both esters. In contrast, other substitution products show a rigid retention of stereochemistry. It is suggested that each ester forms a delocalised ion, and that these ions can subsequently be interconverted. The results contrast with data reported from the study of the nopinol system, but both sets of results have been shown to be consistent with a mechanism of interconversion of ions in which two possible reaction paths exist, the direction of reaction being controlled by the substituent on C-2. Elimination products fit this general pattern except for a very high yield of α-pinene from the cis-ester, which may arise from elimination within an intimate ion pair, rather than from the ‘free’ ion. The trans-ester, in contrast, gives an intimate ion pair which undergoes collapse rather than elimination.