Reagents and conditions:
(a)
1.1 mol equiv PhNCO, methylene chloride, 4 h, rt, 93%. (b) 4 N HCl
in 1,4-dioxane, methylene chloride, 40 h, rt, 96%. (c) 1.5 mol equiv
aldehyde (R defined in Table 1), 9 mol equiv
diisopropylethylamine, 2.5 mol equiv MP-BH(OAc)3, THF,
rt, 24 h, 17–66%.