1,2-Addition of Nucleophiles to Carbonyl Compounds - Carbohydrates: Tools for Stereoselective Synthesis - page 298

Table 13.3

Addition of AlR 3 to aldehydes catalyzed by [Ni(acac) 2 ]/ 41-45. a)

Entry Substrate (R) AlR 3 Ligand L*/Ni Yield (%) ee (%)

1 H AlMe 3 41a 2 15 27 (R)

2 H AlMe 3 41b 2 80 82 (S)

3 H AlMe 3 41c 2 85 89 (S)

4 H AlMe 3 41d 2 87 52 (S)

5 H AlMe 3 41e 2 11 41 (R)

6 H AlMe 3 41f 2 12 10 (R)

7 H AlMe 3 42c 2 100 44 (R)

8 H AlMe 3 43c 2 60 70 (R)

44c 2 64 52 (S)

9 H AlMe 3

10 H AlMe 3 45c 2 52 36 (S)

11 H AlMe 3 41c 1 100 90 (S)

12 H AlEt 3 41c 1 100 88 (S)

13 4-OMe AlMe 3 41c 1 53 94 (S)

14 4-CF 3 AlMe 3 41c 1 95 93 (S)

15 4-CF 3 AlEt 3 41c 1 96 94 (S)

16 2-Cl AlMe 3 41c 1 85 41 (S)

17 3-Cl AlMe 3 41c 1 73 74 (R)

18 4-Cl AlMe 3 41c 1 82 91 (S)

19 4-Cl AlEt 3 41c 1 83 90 (S)

20 4-Cl DABAL-Me 3 41c 1 64 91 (S)

a) Conditions: substrate (0.25 mmol), AlR 3 (0.50 mmol), [Ni(acac) 2 ] (1 mol.%), THF (2 ml), T = − 20 °C.

13.2.3
Zinc-Triflate-Catalyzed Addition of Alkynes to Aldehydes and Imines. N,O Ligands

The addition of acetylene to carbonyl compounds to provide propargyl alcohols
has been rarely studied and there are few methods that give high yields and enan-
tioselectivities. Among the more relevant catalytic systems are chiral oxazaboroli-
dines [21] and the catalytic systems Zn(OTf) 2 /46 [22] or 47 (Figure 13.3) [23].

Ph Me o NO 2 C 6 H 4 CH 2 OTBDMS

HO NMe 2 HO NMe 2

47

46

Figure 13.3 Aminoalcohols 46 and 47.