Bromoform → 7-Bromobicyclo[4.2.0]octa-1,3,5-triene

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In a 250 mL round bottomed flask equipped with a drying tube and a condenser, a solution of cycloheptatriene (30.7 g, 300 mmol), bromoform (25.3 g, 100 mmol), anhydrous K2CO3 (15.0 g, 109 mmol), and 18-crown-6 (0.75 g) was heated with stirring at 145° C. for 9-10 h. The solution was allowed to cool and diluted with an equal volume of acetone. Silica gel (15.0 g) was added to reaction mixture and the insoluble solid residue was separated via vacuum filtration and the filter cake washed with acetone until the washings were colorless. The filtrate was concentrated and distilled to remove residual cycloheptatriene. The viscous, brown residue was precipitated into hot petroleum ether. After filtration to remove the precipitate, the filtrate was concentrated and distilled in vacuo through a Vigreaux column to give slightly impure product. Pure 1-bromobenzocyclobutene was obtained as a light yellow liquid by redistillation yield (2.95 g, 5.94%). 1H NMR (300 MHz, CDCl3) δ 7.28 (m, 1H, ArH), 7.16 (d, 1H, J=7.0 Hz, ArH), 7.07 (d, 1H, J=6.4 Hz, ArH), 5.39 (m, 1H, CH), 3.85 (dd, 1H, J=4.4 Hz, J=14.7 Hz, CH2), 3.45 (d, 1H, J=14.7 Hz, CH2).

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