To a solution of 1.000 g of compound (14) as obtained from example 8 (3.595 mmol) in 40 mL ethanol were added at room temperature 2.215 g cerium (III) chloride (grinded, 8.99 mmol, 2.5 eq). The suspension was placed in an ultrasonic bath for 10 min and was then cooled to 15° C. by a water bath. 2.40 g sodium borohydride (61.1 mmol, 17 eq) were added in 6 portions over 3 h. After additional 2 h at room temperature, the suspension was poured onto 800 mL saturated aqueous sodium hydrogencarbonate/brine (1:1) and the mixture was vigorously stirred for 13 h prior to extraction with five times 400 mL, dichloromethane/ethanol (4:1). The combined organic extracts were evaporated in a rotary evaporator (50° C., 5 mbar). The crude product was obtained as a purple-red solid (879.6 mg, 87% by weight), which was purified by trituration with 5.25 mL dichloromethane/methyl tert-butyl ether (2:1) yielding the title compound (623.2 mg, 2.21 mmol, 61% by weight) as a white solid.
