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. Author manuscript; available in PMC: 2013 Jul 18.
Published in final edited form as: J Am Chem Soc. 2012 Jul 10;134(28):11400–11403. doi: 10.1021/ja305076b

Table 1.

Effect of Amine Protecting Group and Catalyst Structure

graphic file with name nihms392768u1.jpg
entry PG equiv. ald. cat. (R) % yielda drb %eec
1 Cbz 3.0 1 (Me) 66 1.2:1 82
2 Boc 3.0 1 (Me) 62 1.4:1 86
3 Ts 3.0 1 (Me) 86 4:1 90
4 Ns 3.0 1 (Me) 79 6:1 90
5 Ns 1.5 1 (Me) 75 6:1 90
6 Ns 1.5 2 (Bn) 77 9:1 92
a

Isolated yield.

b

Determined by 1H NMR analysis of crude reaction or isolated mixture.

c

Determined by chiral HPLC analysis of corresponding alcohol; absolute stereochemistry assigned by X-ray crystal structure or by analogy.

Boc = t-butoxycarbonyl, Cbz = carboxybenzyl, Ts = 4- toluenesulfonyl, Ns = 4-nitrophenylsulfonyl.