Table 1.
Reaction optimization – asymmetric allylation of benzaldehyde/acetophenone (6 a–b).
|
| |||||
|---|---|---|---|---|---|
|
Entry |
R1 |
R2 |
t [h] |
Conv. [%][a] |
Ee [%][b] |
|
1 |
H (6 a) |
H (7 a) |
2 |
>99 (8 a) |
<1[c] |
|
2 |
H (6 a) |
CO2Et (7 b) |
8 |
>99 (10 a) |
50[c] |
|
3 |
Me (6 b) |
CO2Et (7 b) |
16 |
>99 (10 b) |
70[c] |
|
4 |
Me (6 b) |
CO2Et (7 b) |
16 |
>99 (10 b) |
75[c,d] |
|
5 |
Me (6 b) |
CO2Bn (7 c) |
16 |
>99 (8 d) |
77 |
|
6 |
Me (6 b) |
CO2(CHPh2) (7 d) |
16 |
>99 (89[e], 8 e) |
89 |
|
7 |
Me (6 b) |
CO(NBn2) (7 f) |
16 |
33 (30[e], 8 r) |
11 |
Reaction conditions: aldehyde or ketone (0.1 mmol), zinc (5 eq.), NH4Cl (8 eq.), (S)‐TRIP [(S)‐9, 10 mol‐%], 7 a–d (1.5 eq.) in toluene (1 mL) and cyclohexane (1 mL);
[a] Conversions were determined via HPLC‐UV (215 nm); the product is given in brackets.
[b] The enantiomeric excess was determined on a chiral stationary phase via normal phase HPLC‐UV.
[c] Spontaneous lactonization was observed leading to product 10 a–b.
[d] The reaction was performed at −20 °C.
[e] Isolated yield.