Table 1. Optimization of the Reaction Conditionsa.
| entry | Lewis acid | drd | yield (%) |
|---|---|---|---|
| 1b | – | – | – |
| 2c | Sc(OTf)3 | 92:8:0:0 | 63 |
| 3 | Sc(OTf)3 | 92:8:0:0 | 95 |
| 4 | Er(OTf)3 | 89:11:0:0 | 88 |
| 5 | Yb(OTf)3 | 90:10:0:0 | 90 |
| 6 | Ho(OTf)3 | 88:12:0:0 | 81 |
| 7 | Ce(OTf)3 | 90:10:0:0 | 79 |
| 8 | La(OTf)3 | 91:9:0:0 | 75 |
| 9e | Sc(OTf)3 | 91:9:0:0 | 90 |
| 10f | ScBr3 | 89:11:0:0 | 93 |
a
Reaction conditions: 1a (0.1 mmol), 2 (0.1 mmol), 3 (0.25 mmol), 4 (0.35 mmol), Lewis acid (LA, 20 mol %), dry Py as the solvent (2 mL), 70 °C, N2 atmosphere.
b
Reaction performed in the absence of a Lewis acid and under prolonged heating.
c
With 10 mol % Lewis acid.
d
dr calculated by GC/MS.
e
Gram-scale reaction (see the Supporting Information for details).
f
Reaction using ScBr3 (20 mol %) as a catalyst.