Synthetic study demonstrates efficient polybromination of naphthalene over KSF clay and selective debromination, highlighting a practical route to 2,6-dibromonaphthalene.
Reaction of naphthalene and bromine (three mole equivalents) at room temperature gave 1,4,6tribromonaphthalene (66%) along with 1,4-dibromonaphthalene (8%) and 1,5-dibromonaphthalene (10%). Crystallization of the crude product gave pure 1,4,6-tribromonaphthalene in 50% yield. Bromination of naphthalene using four mole equivalents of bromine over KSF clay gave 1,2,4,6-tetrabromonaphthalene (92%) along with 1,3,5,7-tetrabromonaphthalene (5%). Crystallization of the crude products gave 1,2,4,6tetrabromonaphthalene, a previously unreported compound, and 1,3,5,7-tetrabromonaphthalene in 70% and 4% isolated yields, respectively. Proto-debromination of the crude tetrabromination product, using two mole equivalents of n-butyllithium at a low temperature for a short reaction time, gave 2,6-dibromonaphthalene regioselectively in 82% yield after crystallization.
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Smith et al. (2022) studied this question.
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