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Diastereoselective Synthesis of 4‐Hydroperoxy‐3,5‐cyclohexadienones in the Photooxygenation of Hydroxyethyl‐Substituted Phenols
Author(s) -
Prein Michael,
Maurer Michael,
Peters Eva Maria,
Peters Karl,
von Schnering Hans Georg,
Adam Waldemar
Publication year - 1995
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19950010113
Subject(s) - photooxygenation , chemistry , singlet oxygen , diastereomer , derivative (finance) , solvent , ether , methanol , alcohol , phenols , singlet state , selectivity , medicinal chemistry , stereochemistry , oxygen , organic chemistry , photochemistry , catalysis , excited state , physics , nuclear physics , financial economics , economics
Three of the four possible isomeric para ‐substituted hydroxyethyl‐methylphenols were prepared from readily available starting materials and submitted to photooxygenation. In the case of 3‐hydroxy‐α,6‐dimethylbenzenemethanol ( 1 a ) and 2‐hydroxy‐α,5‐dimethylbenzene‐methanol ( 1 b ) the corresponding 4‐hydroperoxy‐3,5‐cyclohexadienones were obtained as oxy‐functionalized products (⩾90%, 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 π‐facial selectivity of the singlet oxygen attack for the derivative 4‐hydroxy‐α,2‐dimethylbenzenemethanol ( 1 c ). 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 1 a ‐ c . However, in the case of the derivative 1 b , 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 1 d of alcohol 1 c displays a significant lower diastereoselectivity.