The effect of the relative location of the double bond and the alkoxy group on the mass-spectrometric behavior of alkoxydihydropyranes

The mass spectra ofthree 6-alkoxy-Δ3-dihydropyranes and of three 6-alkoxy-Δ2-dihydropyranes have been studied. As distinct from the previously studied 2-alkoxy-Δ3-dihydropyranes, the dominant fragmentation pattern for the compounds under investigation is by retrodiene degradation. Furthermore, in the case of the Δ2-isomers the charge is preferentially localized on the olefin fragment while for the Δ3-isomers, it is located on the diene fragment.