Photorearrangements of Carbomethoxy-Substituted Cyclohexadienones in Neutral Media

Article abstract of DOI:10.1021/jo00238a018

The photochemistry of several 2-carbomethoxy-3-keto-Δ^1,4-hexahydronaphthalenes has been investigated.Unlike analogous bicyclic cyclohexadienones lacking a 2-carbomethoxy substituent, these systems do not undergo normal type-A photorearrangements upon irradiation in nonprotonating solvents.Instead, they afford exocyclic hydroazulenone olefins resulting from proton loss from their angular substituents as well as hydroxy ketones and decarbomethoxylated ethers which have been shown to arise from their derived Zimmerman-Schuster zwitterions by way of intramolecular processes involving attack of the carbomethoxy group upon the electrophilic C-9 center.The behavior of these systems is contrasted with that of a 4-carbomethoxy-substituted dienone and a monocyclic, 2-carbomethoxy-substituted dienone, both of which were found to undergo the expected type-A photorearrangements under neutral conditions.