US2008261972Al, page 24
Sodium triacetoxyborohydride (14.5 g, 68.7 mmol)
was added to a solution of2,3-diaminopyridine (5.00 g, 45.8
mmol) and N-(tert-butoxycarbonyl)-4-piperidone (9.58 g,
48.1 mmol) in dichloroethane (75 mL) at room temperature.
After 5 h, additional sodium triacetoxyborohydride was
added (1.8 g) and again after another 2.5 h. The reaction was
stirred overnight, and quenched with 5% aqueous sodium
hydroxide. This was extracted with methylene chloride, and
washed with 5% aqueous sodium hydroxide, water and saturated
sodium chloride solution. After drying over sodium
sulfate, the solution was filtered and evaporated to give the
crude product. This was purified by chromatography (silica
gel, 3 to 5% methanol in methylene chloride gradient elution),
which gave the title compound (4.44 g). MS 293 (M+ I)
IHNMR(500MHz, CD30D) 67.32 (dd, J=5, I Hz, lH), 6.85
(dd, J=8, I Hz, lH), 6.59 (dd, 5 Hz, lH), 4.04 (d, J=13
Hz, 2H), 3.46 (m, lH), 2.98 (br s, 2H), 2.01 (dd, J=12, 2 Hz,
2H), 1.46 (s. 9H), 1.37 (qd. J=12. 4 Hz, 2H).
Step B. 2-0xo-l-(l-tert-butoxycarbonylpiperidin-4-
