Preparation of Regioselectively Protected Hydroquinones by Phosphorylation of p-Benzoquinones with Trialkyl Phosphites

Article abstract of DOI:10.1002/hlca.19840670529

The title reaction has been applied to 10 monosubstituted p-benzoquinones (Scheme 2, Table).The regioselectivity of the O-phosphorylation is influenced by bulky substituents (t-butyl and trimethylsilyl) and, electronically, by the methoxy group.The regioselectivity, which is high in nonpolar media (benzene), is lower in polar solvents (CH2Cl2 and CH3CN).The synthetic potential of this transformation, exemplified by the preparation of compounds 29 (Scheme 3) and 32 (Scheme 4), is considerably extended by applying milder methods for the phosphate hydrolysis and by using the reagent couple P(OCH3)3/trimethylsilyl chloride, which gives clean access to p-hydroxyphenyl phosphates. p-Benzoquinones 4h and 4i with strong ?-acceptor substituents react in a different way, giving phosphonates.The electronically induced regioselectivity of the O- and C-phosphorylation is in accordance with the preferences expected for the attack by a nucleophilic phosphorylation agent.