Structure and spectral properties of two novel isomeric 2,4-dimethyl- 2-methoxy-3,8-dioxabicyclo [3.2.1] octanes

The preparation and structure of the novel bicyclic ketals 5 and 6 is reported. A single crystal X-ray structure of compound 5 establishes the structures of 5 and 6. ¹H and ¹³C NMR spectra are interpreted in terms of chair conformations for both 5 and 6, even though an unfavorable syn-diaxial interaction is present in 6. In the ¹H spectra, the axial C-4 proton of compound 5 absorbs downfield of its equatorial counterpart in 6. This is apparently due to a deshielding effect of the syn-diaxial C-2 methoxy group in compound 5.