Abstract
The preparation of 5-bromo-2-naphthol (4) in three steps from 5-amino-2-naphthol (1) is described. A sulfonic acid group is introduced at the 1-position as an activating and protecting group for the Sandmeyer reaction. The sulfonate group allows for the use of only water and sulfuric acid as solvents. The sulfonic acid is introduced with three equivalents of sulfuric acid, and it is removed in 20% aq. sulfuric acid.
Highlights
Regioselective synthesis of disubstituted naphthalenes can be challenging especially when the substituents are on different rings
Even when the hydroxyl group is protected as a methyl ether, the normal solution-phase Sandmeyer reaction employing cuprous salts is still problematic
In this paper we describe the use of sulfonation as a way to both activate the Sandmeyer reaction while protecting the naphthalene nucleus from further substitution
Summary
Regioselective synthesis of disubstituted naphthalenes can be challenging especially when the substituents are on different rings. A sulfonic acid group is introduced at the 1-position as an activating and protecting group for the Sandmeyer reaction. The sulfonate group allows for the use of only water and sulfuric acid as solvents. The sulfonic acid is introduced with three equivalents of sulfuric acid, and it is removed in 20% aq. The most direct route to 4 is from 5-amino-2-naphthol (1) using the Sandmeyer reaction.
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