The conformational analysis of saturated heterocycles. Part X. Steric requirements of the nitrogen lone pair from aza-cis-decalin equilibria

Abstract

The methoxide-catalysed equilibration of cis- and trans-1-methoxycarbonyl-cis-decalin has been studied over the range 25–106° in methanol and in glyme by gas chromatography. The equilibration of cis- and trans-4-methoxycarbonyl-1-methyl-1-aza-cis-decalin in methanol, n-propanol, glyme, and diglyme was studied at 25–85° by conductimetric analysis, and involved isolation of the cis-cis-derivative* by preferential reaction of its isomer with methyl iodide. The results were combined to show that in non-hydrogen-bonding solvents the conformer with the lone pair “inside” is considerably more stable than the other, whereas in hydrogen-bonding solvents there is little preference. The results are discussed in terms of the steric requirements of free and solvated lone pairs.