Synthesis and Coupling reaction of 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene

4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene is a white to off‑white solid powder under ambient temperature and pressure, exhibiting excellent chemical stability and notable fluorescent properties. It is insoluble in water but soluble in alcoholic organic solvents and chloroform. In the pharmaceutical industry, 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene is primarily used as a synthetic intermediate for the drug molecule dapagliflozin, serving as a key building block in its industrial synthesis. Dapagliflozin, a sodium‑glucose cotransporter‑2 (SGLT‑2) inhibitor class of oral hypoglycemic agents, was the first globally approved SGLT‑2 inhibitor and became the first SGLT2 inhibitor launched in China in 2017. The drug lowers blood glucose by inhibiting renal tubular reabsorption of glucose and promoting urinary glucose excretion, featuring non‑insulin‑dependent mechanisms while also providing antihypertensive and renal‑protective effects.

Synthesis

Method 1

A patent has reported a synthetic method for preparing 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene. The process involves first chlorinating o‑chlorobenzoic acid to obtain o‑chlorobenzoyl chloride, followed by Friedel‑Crafts acylation to yield 2‑chloro‑4'‑iodobenzophenone. This intermediate is then brominated to give 5‑bromo‑2‑chloro‑4'‑iodobenzophenone, which is subsequently reduced to 5‑bromo‑2‑chloro‑4'‑iodobenzylbenzene. Finally, a substitution reaction affords the target compound, 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene. The described route is concise, yields high‑purity product, employs readily available raw and auxiliary materials, uses low‑toxicity solvents that can be recycled, generates no phosphorus‑containing wastewater, and is safe, environmentally friendly, cost‑effective, and suitable for industrial production due to its modest equipment requirements. [1]

Method 2

A patent has disclosed a one‑pot synthesis method for 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene. The process consists of the following sequential steps: starting from 2‑chloro‑5‑bromobenzoic acid, reaction with thionyl chloride yields 2‑chloro‑5‑bromobenzoyl chloride. This intermediate is then treated with an organic solvent, a Lewis acid, phenetole, and a borohydride reagent to carry out Friedel‑Crafts acylation followed by borohydride reduction, affording 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene. The advantages of the process include the use of the same Lewis acid as the catalyst for both the Friedel‑Crafts acylation and the borohydride reduction, which significantly reduces catalyst consumption. The operation is simple, requires no isolation or purification of intermediates, and enables the synthesis of 5‑bromo‑2‑chloro‑4'‑ethoxybenzylbenzene in one step through precise control of reaction conditions, addition sequence, and reagent ratios. Moreover, the process generates minimal waste, offers efficient solvent recovery, and features low production costs. [2]

Synthesis of β-Glucopyranose

Researchers designed and synthesized 1-[3-(3‑benzyl‑4‑ethoxybenzyl)‑4‑chlorophenyl]‑1,6‑dideoxy‑β‑D‑glucopyranose. Starting from 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene as the raw material, the target compound was obtained through a sequence of Friedel‑Crafts acylation, reduction, nucleophilic addition, reductive acetylation, and deacetylation reactions. The structure of the target compound was confirmed based on its physicochemical properties and spectroscopic data, achieving an overall yield of 32% and a mass fraction of 98.48%. The synthesis of 1-[3-(3‑benzyl‑4‑ethoxybenzyl)‑4‑chlorophenyl]‑1,6‑dideoxy‑β‑D‑glucopyranose provides a convenient route for studying impurities in tianagliflozin.

Coupling reaction

Figure1: Coupling reaction of 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene

In a 100 mL three‑necked flask equipped with a stir bar under an argon atmosphere, 2 mmol of 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene, 0.06 mmol of Pd(PPh₃)₂Cl₂ (42 mg, 0.03 equiv.), 0.12 mmol of CuI (23 mg, 0.06 equiv.), 2.4 mmol of trimethylsilylacetylene (236 mg, 1.2 equiv.), and 10 mL of diisopropylamine as solvent were charged. The reaction mixture was then placed in a pre‑heated oil bath at 50°C for 12 hours, with the progress monitored by thin‑layer chromatography (TLC). After completion, the solvent was evaporated under reduced pressure, and the residue was diluted with 30 mL of ethyl acetate. The mixture was filtered through a thin pad of Celite, and the filtrate was washed with water (3 × 5 mL) before being concentrated. [3]

Pharmaceutical Applications

5‑Bromo‑2‑chlorobenzoic acid is first converted to its acyl chloride, followed by a Friedel‑Crafts reaction with phenetole to give the corresponding ketone. The carbonyl group is then reduced to yield 4-Bromo-1-chloro-2-(4-ethoxybenzyl)benzene. This intermediate is subsequently condensed with 2,3,4,6‑tetra‑O‑trimethylsilyl‑D‑glucopyranos‑1,5‑lactone (3), and the anomeric hydroxyl group is etherified. After deprotection, 2‑chloro‑5‑(1‑methoxy‑D‑glucopyranos‑1‑yl)‑4'‑ethoxybenzylbenzene (7) is obtained. The methoxy group is then reductively removed using Et₃SiH/BF₃·OEt₂, followed by acetylation and hydrolysis to afford the hypoglycemic drug dapagliflozin, with an overall yield of approximately 40%. [4]

Reference

[1] Gao, P.; Shen, B. L.; Wei, W.; et al. A method for synthesizing 5-bromo-2-chloro-4'-ethoxybenzylbenzene: CN202210030161.X[P].

[2] Yu, Y. K.; Ji, Y. F. Synthesis of Dapagliflozin [J]. Chinese Journal of Pharmaceuticals, 2011, 42(002): 84-87.

[3] Liu, Tao; et al, Synthesis of P-stereogenic cyclic phosphinic amides via electrochemically enabled cobalt-catalyzed enantioselective C-H annulation, Green Chemistry (2023), 25(9), 3606-3614

[4] Sun, G. F.; Chen, C. H.; Huang, J. W.; et al. One-pot synthesis method of 5-bromo-2-chloro-4'-ethoxybenzylbenzene: CN201210249929.9[P].

You may like