Benzoyl Peroxide → 4-(4-Trifluoromethylbenzoyl)-3-chloro-5-methylbenzyl azide

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A stirred mixture of 1-(4-trifluoromethylbenzoyl)-2-chloro-4,6-dimethylbenzene (6.90 g, 22.1 mmol), N-bromosuccinimide (3.94 g, 22.1 mmol), and dibenzoyl peroxide (224 mg, 0.925 mmol) in dry carbon tetrachloride (180 ml) was refluxed 44 hours. Additional N-bromosuccinimide (1.97 g, 11.1 mmol) was added and the mixture was refluxed 24 hours. The mixture was cooled to 0° C., filtered, and washed with carbon tetrachloride. The combined filtrate and washes were evaporated to dryness under vacuum, and the residue was dissolved in dichloromethane (135 ml), treated with tetramethylguanidinium azide (7.25 g, 45.8 mmol), and stirred 40 minutes at ambient temperature. Solvent was removed under vacuum and the residue was stirred with diethyl ether (180 ml). The mixture was filtered and the precipitate was washed with diethyl ether. The combined filtrate and washes were washed twice with water and once with brine, dried over anhydrous magnesium sulfate, and evaporated to dryness under vacuum. The residue was dissolved in hexane (300 ml) and decanted, and the residual gum was washed with hexane. The combined hexane layers were evaporated to dryness under vacuum. The residue was chromatographed on silica gel (500 g) eluted with 93:7 (v/v) hexane-ethyl acetate using a preparative high-performance liquid chromatograph to provide 1.71 g (22%) oily 4-(4-trifluoromethylbenzoyl)-3-chloro-5-methylbenzyl azide (A), 1.30 g (17%) 2-(4-trifluoromethylbenzoyl)-3-chloro-5-methylbenzyl azide (B), and 0.48 g of a mixture of A and B.

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