Adducts of Anthrahydroquinone and Anthranol with Lignin Model Quinone Methides. 2. Dehydration Derivatives. Proof of Threo Configuration

Article abstract of DOI:10.1021/jo00151a018

NMR studies of novel dehydration derivatives of anthrahydroquinone (AHQ)-lignin and anthranol-lignin model quinone methide adducts have confirmed the sole diastereomeric form of the adducts as "threo".Upon dehydration of the AHQ adduct 1-(3,4-dimethoxyphenyl)-1-(10-hydroxy-9-oxoanthracen-10-yl)-2-(2-methoxyphenoxy)propane with polyphosphoric acid, the spiro compound 3'-(3,4-dimethoxyphenyl)-2',3'-dihydro-8'-methoxy-2'-methylspirobenzopyran>-10-one (3b) was obtained.Reduction of the anthranol adduct 1-(3-methoxy-4-hydroxyphenyl)-1-(9-oxoanthracen-10-yl)-2-(2-methoxyphenoxy)pro pane with LiAlH4, followed by dehydration with BF3*Et2O gave the bicyclic compound 10,11-dihydro-2,3-dimethoxy-11-<1-(2-methoxyphenoxy)ethyl>-5,10-o-benzeno-5H-dibenzocycloheptene (7d).Coupling constants of the aliphatic protons in 3b and 7d are consistent only with the threo form.Therefore, by analogy, all other reported AHQ and anthranol adducts with asymmetry of Cα and Cβ are assigned the threo configuration.