Byproducts in the cyclization of ψ‐ionone to β‐ionone; structural determination of two new ionone isomers

Abstract It is shown that the well known acid‐catalysed cyclization of ψ‐ionone leads to the formation of small amounts of the spiro‐dihydrofuran XV, the cyclohexadienylic ketone XVI, and the unsaturated ketones XVIIa and b. These are all isomers of ionone; the first two have hitherto not been described in the literature, whereas XVII has been obtained by a different route as a mixture of cis‐trans isomers. The structural proof of these products is based mainly on spectroscopic data.