Publisher Summary Carbonium ions can undergo a variety of photoreactions, affording products, which often vary considerably from those obtained in the photolysis of the corresponding uncharged compounds. The predominant mode of reaction encountered is the isomerization to one or more valence bond isomers, which occurs via a symmetry-allowed disrotatory electrocyclic closure, rather than a [σ2 a +π2 a ] cyoloaddition in the case of alkylbenzenium ions and protonated cyclohexadienones. Where valence isomerization is precluded, electrocyclic ring opening reactions, or electron transfer and subsequent coupling are observed. In the case of the trityl cation, many pathways may become operative, depending primarily on the acidity of the medium in which the reaction is carried out. While only the most elementary mechanistic studies have been undertaken, their results indicate that it is the excited singlet which is the reactive species in some instances, while the triplet undergoes reaction in others.

The Photochemistry of Carbonium Ions

The photochemistry of protonated unsaturated carbonyl compounds

This review, which covers the literature up to 1992, gives information on the occurrence in nature, the practical use, the synthesis, and the chemical transformations of oxygen-containing terpenoids of the 1,1,4-trimethylcycloheptane series.

Oxygen-containing terpenoids of the 1,1,4-trinethylcycloheptane series

Zwei neue verbindungen durch photoisomerisierung von eucarvon

Irradiation of eucarvone (I) adsorbed on silica gel or in trifluoroethanol gives, in addition to the two expected products (IIa and IIb), the bicyclo[4,1,0]enone (V), which subsequently undergoes[1,3]sigmatropic photorearrangement to dehydrocamphor (IV) and a cyclobutanone (VI).

Harold Hart

Papers

Two new products from the photoisomerization of eucarvone