(4S)-7-(3,5-Dimethylisoxazol-4-yl)-4-pyridin-2-yl-4,5-dihydroimidazo[1,5,4-de][1,4]benzoxazine-2-carbaldehyde (15 mg, 0.042 mmol) and dimethylamine hydrochloride (0.0041 g, 0.050 mmol) [Aldrich, cat. #126365] were dissolved in acetonitrile (1.5 mL) at room temperature. To the resulting mixture, copper(II) sulfate pentahydrate (0.0005 g, 0.002 mmol) [Aldrich, cat. #209198], calcium carbonate (0.0046 g, 0.046 mmol) [Aldrich, cat. #C6763] and 6.0 M tert-butyl hydroperoxide in decane (0.0076 mL, 0.046 mmol) [Aldrich, cat. #416665] were added. The reaction vessel was capped, degassed, and allowed to stir at 40° C. for 10 hours. After filtration through Celite, the solution was concentrated and the resulting residue was purified by preparative LCMS (XBridge C18 column, eluting with a gradient of acetonitrile/water containing 0.1% ammonium hydroxide, at flow rate of 60 mL/min) afforded the following three compounds:
