7-(2-methyl-1H-benzimidazol-6-yl)-2,3,4,5-tetrahydro-1,4-benzoxazepine dihydrochloride (6.95 g, 19.73 mmol) was suspended in dichloromethane (100 mL) and cooled to 0° C. To the resulting mixture was added DIPEA (19 mL, 109 mmol) followed by allyl chloroformate (4.6 mL, 43.4 mmol) and stirring was continued at 0° C. for 30 minutes then warmed to room temperature. The reaction mixture was then charged with additional DIPEA (3.4 mL) and allyl chloroformate (1 mL) then stirred an additional 30 minutes at room temperature. The resulting solution was then concentrated and the residue azeotroped once from methanol (100 mL). The residue was then taken back into methanol (100 mL) followed by portionwise addition of 2 M aqueous sodium hydroxide (20 mL) and the mixture was allowed to stir for 1 h at room temperature. The solution was then concentrated and the residue partitioned with chloroform and dilute brine. The organic phase was then dried over anhydrous sodium sulfate, filtered and concentrated to give prop-2-en-1-yl 7-(2-methyl-1H-benzimidazol-6-yl)-2,3-dihydro-1,4-benzoxazepine-4(5H)-carboxylate as an amorphous residue which was carried forward directly into step 6.
