Trimethyl orthoformate → 3-(2-Propenyl)-2-tetralone Ethylene Ketal

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A mixture of 3-(2-propenyl)-2-tetralone (25.9 g, 139 mmol), trimethyl orthoformate (61.3 ml, 554 mmol), ethanediol (57.5 ml, 1.03 mol), p-toluenesulfonic acid monohydrate (0.27 mg, 1.4 mmol) in dichloromethane (650 ml) was stirred at room temperature, under argon for 2 h. Resulting mixture was partitioned between saturated aqueous sodium bicarbonate (1000 ml) and dichloromethane (3×500 ml). The combined organic extracts were washed with brine (500 ml), dried (Na2SO4) and evaporated in vacuo to give a brown oil (34.9 g). Chromatography on silica using 0-10% ether-hexane gradient elution gave the title compound as a yellow oil (20.1 g, 63%).

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