o-Quinone Methide Intermediates and Their Role in Coordinated Reactions of Magnesium Phenoxides with α-Branched Aliphatic Aldehydes

Article abstract of DOI:10.1021/jo00169a036

The reactions of (aryloxy)magnesium bromides with α-branched aliphatic aldehydes in apolar solvents have been investigated in order to obtain information on the role of o-quinone methide intermediates 8 or 9 in controlling the selectivity of the reactions of phenolic substrates and carbonyl compounds, which usually give a complex mixture of products.These reactions are characterized by high ortho regioselectivity, giving 2,2'-alkylidenebis(phenols) (3), 2-alkenylphenols (4), and 2,2-dialkyldihydrobenzofurans (5), according to the nature of the substituents on the aldehyde and the phenolic substrates. o-Quinone methides have been proved to be intermediates in these coordinated reactions by trapping experiments.The observed reaction pathways have been explained with the assumption that the steric bulkinesss of the substituents leads the o-quinone methides to assume a geometry (8 or 9) that determines the subsequent reaction course.