75849-32-0Relevant articles and documents
Intramolecular Alkylation of Phenols. Part 5. A Regiospecific Anionic Ring Closure of Phenols via Quinone Methides
Murphy, William S.,Wattanasin, Sompong
, p. 1567 - 1577 (2007/10/02)
The bis-magnesium salts of the triols (6a) and (6h) cyclise when heated in benzene with high ortho-regiospecificity to the corresponding bis-phenols (7) and (8).The triols (6k) and (6o) under the same conditions cyclise with high para-regiospecificity to the corresponding bis-phenols (7) and (8).Both (6a) and (6h) cyclise via o-quinone methides, and (6k) and (6o) via p-quinone methides.Results from the use of, inter alia, 18-crown-6, indicate that the high ortho-regiospecificity of the cyclisation of (6a) and (6h) is due to intramolecular Mg(II) bridging of the intermediate o-quinone methides.The high para-regiospecificity of cyclisation of (6k) and (6o) is due to steric hindrance towards o-cyclisation of the intermediate p-quinone methides presented by the Mg(II) cation.The unexpected facility with which (6a) and (6k) undergo ring closure is discussed.