[NH2:1][C:2]1[CH:3]=[C:4]([C:12]([O:14][CH3:15])=[O:13])[C:5]2[O:10][CH2:9][CH2:8][O:7][C:6]=2[CH:11]=1.[B:16](F)([F:18])[F:17].CCOCC.[N:25](OC(C)(C)C)=O>COCCOC>[CH3:15][O:14][C:12]([C:4]1[C:5]2[O:10][CH2:9][CH2:8][O:7][C:6]=2[CH:11]=[C:2]([N:1]=[N-:25])[CH:3]=1)=[O:13].[F:17][B+:16][F:18]A solution of methyl 7-amino-2,3-dihydro-1,4-benzodioxine-5-carboxylate (4.89 g, 23.3 mmol) in ethylene glycol dimethyl ether (15 mL) was cooled to −5° C. and then slowly added boron trifluoride diethyl etherate (3.85 mL, 30.3 mmol) followed by tert-butyl nitrite (3.05 mL, 25.6 mmol). The resulting gray suspension was allowed to warm to 0° C. and stirred for 1 h, at which time it was filtered and rinsed with ethyl acetate to give 6.24 g (93%) of difluoroboranylium {8-[(methyloxy)carbonyl]-2,3-dihydro-1,4-benzodioxin-6-yl}diazenide as a gray powder: 1H NMR (400 MHz, d6-DMSO): 8.73 (br s, 1H), 8.32 (br s, 1H), 4.64 (br m, 2H), 4.47 (br m, 2H), 3.88 (s, 3H).
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