Synthesis and NMR studies of substituted spiro[5,5]undecanones and derived bicyclic compounds

Abstract

A detailed study has been made into the preparation, structure, and characterization of a series of arylspiro[5,5]undecanones and derived compounds. This family of spiroundecanones is exemplified by the parent structure, A, which was modified to give the polycyclic compounds B. Several ring-cleaved derivatives of type C were also prepared. The general structural features of these systems make them very useful for proton NMR investigations of "perpendicular" or "out-of-plane" diamagnetic ring-current shifts. The axial methylene or R' group at C-5 is in the region of this diamagnetic shielding, and its chemical shift is observed upfield relative to a normal methylene (or vinyl) group. The total magnitude of this upfield shift has been shown to be larger than that of the methyl group shift observed in similar compounds. The primary factor causing differences in these methylene (or vinyl) group shifts has been shown to be the conformational mobility of the group observed, angle factors being of lesser importance, and these results are discussed. In molecules of type B where some functionality is present at the 9 position, the observed shift of the axial C-5 methylene group was not found to be the result of simple addition of aromatic ring current and β-substituent effects. The carbon-13 NMR spectra of all compounds have been measured, and the carbon chemical shift assignments have been tabulated. Aromatic ring-current effects have been shown to be very small, or non-existent, except in the case of edge effects where significant shifting is observed.