Enantiospecific sp(2)–sp(3) Coupling of ortho‐ and para‐Phenols with Secondary and Tertiary Boronic Esters

The coupling of ortho‐ and para‐phenols with secondary and tertiary boronic esters has been explored. In the case of para‐substituted phenols, after reaction of a dilithio phenolate species with a boronic ester, treatment with Ph(3)BiF(2) or Martin's sulfurane gave the coupled product with complete enantiospecificity. The methodology was applied to the synthesis of the broad spectrum antibacterial natural product (−)‐4‐(1,5‐dimethylhex‐4‐enyl)‐2‐methyl phenol. For ortho‐substituted phenols, initial incorporation of a benzotriazole on the phenol oxygen atom was required. Subsequent ortho‐lithiation and borylation gave the coupled product, again with complete stereospecificity.