CLAISEN REARRANGEMENTS AND CYCLIZATIONS IN PHENYL PROPARGYL ETHERS UNDER ELECTRON-IMPACT CONDITIONS

An interesting Claisen rearrangement has been observed in phenyl propa rgyl ether, yielding significant amounts of the [M - CO] ion under ele ctron impact conditions. The other competing pathway is the loss of a hydrogen radical from M.+ furnishing the most abundant ion in its mass spectrum. Expulsion of a hydrogen radical from the propargylic carbon leads to the propargylic cation species, while ejection of the ortho hydrogen gives rise to a benzopyrylium cation structure. Substituents on the phenyl ring do not favour the Claisen rearrangement, whereas ej ection of the substituents producing benzopyrylium cations gains impor tance. The mechanisms and ion structures proposed are supported by hig h-resolution data, B/E and B2/E linked-scan spectra, Collision Activat ed Decomposition (CAD)-B/E linked-scan spectra and deuterium isotope l abelling.