Solvent shifts induced by benzene in triterpenes as an aid to structure elucidation

Abstract

Solvent shifts for protons in several derivatives of the triterpenes oleanene and lupane are reported. It is found that in general only those Me groups which are close to a polar group exhibit appreciable solvent shifts. In the compounds examined, an axial proton on the same C atom as an equatorial acetate function exhibits a characteristic downfield shift in benzene solution. In contrast, equatorial protons attached to the same C atom as the oxygen of a γ-lactone bridge exhibit an upfield shift in benzene solution. As a general rule, protons which lie in regions of high electron density tend to be deshielded in benzene solution.