166327-63-5Relevant articles and documents
Diastereoselective Synthesis of 4-Hydroperoxy-3,5-cyclohexadienones in the Photooxygenation of Hydroxyethyl-Substituted Phenols
Prein, Michael,Maurer, Michael,Peters, Eva Maria,Peters, Karl,Schnering, Hans Georg von,Adam, Waldemar
, p. 89 - 94 (2007/10/02)
Three of the four possible isomeric para-substituted hydroxyethylmethylphenols were prepared from readily available starting materials and submitted to photooxygenation.In the case of 3-hydroxy-α,6-dimethylbenzenemethanol (1a) and 2-hydroxy-α,5-dimethylbenzenemethanol (1b) the corresponding 4-hydroperoxy-3,5-cyclohexadienones were obtained as oxy-functionalized products (>/= 90percent, d.r. 85:15 and 75:15).The stereochemistry of the products was assigned after reduction to the corresponding p-quinols.The ready cleavage of the initial oxygenated product, which can be observed at low temperature as a single diastereomer, prevented rigorous assignment of the ?-facial selectivity of the singlet oxygen attack for the derivative 4-hydroxy-α,2-dimethylbenzenemethanol (1c).The present stereochemical results indicate that the hydroxyl group directing effect, that is, coordination of the incoming singlet oxygen dienophile with the hydroxyl group, is also operating in the photooxygenation of the chiral phenols 1a-c.However, in the case of the derivative 1b, hydrogen bonding in the starting material leads to an opposite stereochemical outcome.This conclusion is further substantiated by solvent effects and the fact that the methyl ether 1d of alcohol 1c displays a significant lower diastereoselectivity. - Keywords: chiral phenols * facial selectivity * photooxidations * quinols * singlet oxygen
