To a stirred solution of the product of Example 41F (13.80 g, 31.41 mmol) in dimethylacetamide (500 mL) was added a solution of 37% aqueous formaldehyde (7.2 mL, 94.23 mmol, 3.0 equivalents) followed by sodium triacetoxyborohydride (20.0 g, 94.23 mmol, 3.0 equivalents). The mixture was stirred at 25+/−5° C. for 30 minutes during which the starting material was consumed, giving a clear solution. The mixture was diluted with 1N HCl (94 mL, 94 mmol, 3 equivalents) and stirred for one hour. The mixture was adjusted to pH 9.0+/−0.5 with 1N NaOH (335 mL). The mixture was stirred for 1 hour then filtered. The wet cake was washed with water and dried in a vacuum oven at about 50° C. to provide the title compound (10.40 g, 88.9%).
