The Use of Supported Zinc Bromide for the Fast and Selective Bromination of Aromatic Substrates

Abstract

Zinc bromide supported on acid activated montmorillonite (K-10) or mesoporous silica (100 Å) is a fast, selective catalyst for the para-bromination of activated and mildly deactivated aromatic substrates. The optimum loading of zinc bromide on K-10 is 1.25 mmol/g and 1.75 mmol/g on the higher surface area silica (100 Å). Thermal activation of these catalysts at 200 °C results in optimum activity and selectivity. Also, system optimisation has allowed harmful chlorinated solvents to be replaced by less damaging hydrocarbon solvents.

Scalable Synthesis of a Prostaglandin EP4 Receptor Antagonist

“…Ketone 12 was unreactive toward direct bromination by NBS or elemental bromine. However, in the presence of as little as 1 mol % ZnCl 2 , clean conversion to 13 occurred upon treatment with bromine within 30 min at 0 °C . Importantly, bromination of the benzylic positions was not observed, even in the presence of excess bromine.…”