Hydride Reductions and 1,2-Additions of Nucleophiles to Carbonyl Compounds Using Carbohydrate-Based Reagents and Additives - Carbohydrates: Tools for Stereoselective Synthesis - page 128

Table 6.2 Summary of the best results obtained in the asymmetric reduction of carbonyl
compounds with sodium borohydride and monosaccharide ligand 9a.

O

OOH

O

O O 9a

O OH

NaBH 4

R 1 R 2 R 1 R 2

Entry R 1 R 2 NaBH 4 (equiv.) 9a (equiv.) Additive (equiv.) Yield (%) ee (%)

1 Et Ph 1 2 — 78 39 (R)

2 Et Ph 1 2 (Me) 2 CHCO 2 H (1.2) 55 83 (R)

3 Et Ph 1 2 ZnCl 2 (0.5) 66 88 (S)

4 Et Ph 1 2 AlCl 3 (0.3) 55 54 (R)

Table 6.3 Selected examples of the asymmetric borohydride reduction of ketones catalyzed by
amphiphilic dendrimers.

OH

O

N

OH

HO
HO

H G3

HO

O

15

32

O OH

15 (3 mol%)
NaBH 4 (10 mol%)

R 1 R 2 R 1 R 2

Entry R 1 R 2 a) T (°C) Solvent Yield (%) ee (%)

1 Cy Ph 25 THF 97 97 (S)

2 Cy Ph 25 H 2 O 95 50 (S)

3 Bu Ph 25 THF 96 100 (S)

4 Me Ph 0 THF 94 99 (S)

5 Me Ph 25 H 2 O 95 50 (S)

6 b)

Me Ph 25 H 2 O 92 98 (S)

7 Me p -Br-Ph 25 THF 94 78 (S)

8 Me C 5 H 11 -20 THF 94 28 (S)

9 Me C 5 H 11 -80 THF 96 96 (S)

10 Me o -Py 0 THF 90 90 (S)

a) Py = pyridine.

b) Using fourth-generation dendrimer (G4).