Table 1.
Conditions optimization for the direct asymmetric visible-light-excited [2 + 3] photocycloadditiona
| |||||
|---|---|---|---|---|---|
| Entry | Catalystb | 1 | Solvent | Yield (%)c | ee (%)d |
| 1 | Λ–RhS (8.0) | 1a (R1 = R2 = Me) | acetone (0.2 M) | 54 (3a) | 86 |
| 2 | Λ–RhS (8.0) | 1b (R1 = R2 = H) | acetone (0.2 M) | 75 (3b) | 72 |
| 3 | Λ–RhS (8.0) | 1c (R1 = C6H5; R2 = H) | acetone (0.2 M) | 83 (3c) | 87 |
| 4 | Λ–RhS (8.0) | 1c | CH2Cl2 (0.2 M) | 55 (3c) | 84 |
| 5 | Λ–RhS (8.0) | 1c | CDCl3 (0.2 M) | 93 (3c) | 92 |
| 6 | Λ–RhS (8.0) | 1c | CDCl3 (0.1 M) | 98 (3c) | 95 |
| 7 | Λ–RhS (4.0) | 1c | CDCl3 (0.1 M) | 80 (3c) | 92 |
| 8 | Λ–RhS (4.0) | 1d (R1 = Me; R2 = H) | CDCl3 (0.1 M) | 82 (3d) | 92 |
| 9 | Λ–RhS (4.0) | 1e (R1 = 4-FC6H4; R2 = H) | CDCl3 (0.1 M) | 80 (3e) | 92 |
| 10 | Λ–RhS (4.0) | 1f (R1 = PMP; R2 = H) | CDCl3 (0.1 M) | 92 (90)e (3f) | 94 |
| 11 | Λ–RhS (4.0) | 1f | CHCl3 (0.1 M) | 90 (3f) | 94 |
| 12f | Λ–RhS (4.0) | 1f | CDCl3 (0.1 M) | 90 (3f) | 94 |
| 13f | Λ–IrS (4.0) | 1f | CDCl3 (0.1 M) | 50 (3f) | 0 |
| 14f | None | 1f | CDCl3 (0.1 M) | 7 (3f) | n.a. |
| 15f,g | Λ–RhS (4.0) | 1f | CDCl3 (0.1 M) | 0 (3f) | n.a. |
PMP 4-methoxyphenyl. n.a. not applicable
aReaction conditions: N-Acylpyrazole 1 (0.10 mmol), vinyl azide 2a (0.125 mmol) and the shown amount of catalyst in solvent were stirred at room temperature under an atmosphere of nitrogen with irradiation of blue LEDs (24 W)
bCatalyst loadings in mol% provided in brackets
cNMR yields
dOnly one diastereoisomer observed judged by NMR and enantiomeric excess determined by HPLC analysis on chiral stationary phase
eIsolated yield provided in parenthesis
fAssembled in air, then sealed the tube
gUnder dark