2001 Volume 59 Issue 7 Pages 689-696
Photochemical cyclization of substituted o-alkylphenyl ketones and the thermal and acid-catalyzed reactions of the resulting benzocyclobutenols are described. The selective thermal ring opening of the benzocyclobutenol to the E-dienol was elucidated using the deuterated benzocyclobutenol and by thermal interconversion between two diastereomeric benzocyclobutenols. The 2, 2-dimethylbenzocyclobutenols having a hydroxy group on the β-carbon of the quaternary C1-alkyl group underwent stereospecific thermal isomerization by a 1, 5-sigmatropic hydrogen shift to give the 2-isopropenylphenyl alcohol through a twisted E-dienol. The benzocyclobutenols having a keto group on the β-carbon of the quaternary C1-alkyl group underwent thermal retro-aldol cleavage to give benzocyclobutenones. Acid-catalyzed reaction of benzocyclobutenols having α, α-dimethyl and β-hydroxy or β-acetoxy groups in their C1-alkyl chain gave isopropylidenebenzocyclobutene.
