A stereodynamic investigation of antivitamins K in the dicoumarol series. II. Differentiation between the two hydroxyl groups by the nuclear Overhauser effect

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Abstract
Dicoumarol derivatives, substituted at the bridgehead, show a double restricted rotation. This hindered rotation is manifest through the appearance of two signals, the hydroxyl protons being diastereotopic at low temperatures.In this work we assign the two respective signals by the nuclear Overhauser effect. The high-field signal corresponds to a hydroxyl site close to the bridgehead tertiary proton, while the other corresponds to a site in proximity to the substituent R. The case of structurally analogous dimethones has been investigated by the same technique with identical conclusions. This disproves the interpretation made previously on the basis of steric and anisotropic effects.The interatomic distances concerned have been calculated, and these have yielded an estimate of deformations induced by the bridgehead substituents.Evidence is supplied for the different behavior of the two sites and this study gives evidence for a very facile intermolecular chemical exchange of the hydroxyl site close to the tertiary bridgehead proton in the presence of traces of protonated compounds.The overall behavior is the result of the asymmetry of the molecules of this series in their chelated form.

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