Table 1. Optimization of 6-Endo Cyclization of 1a.
| entry | [Pd] | [O] | L | t (h) | 2a (%) |
|---|---|---|---|---|---|
| 1 | Pd(OAc)2a | Cu(OAc)2b | - | 30 | -c |
| 2 | Pd(OAc)2a | p-BQb | - | 30 | -c |
| 3 | Pd(OAc)2a | PhCO3tBud | - | 24 | 9 |
| 4 | Pd(dba)2a | PhCO3tBud | - | 24 | 5 |
| 5 | PdCl2(CH3CN)2a | PhCO3tBud | - | 8 | 10e |
| 6 | PdCl2(CH3CN)2a | PhCO3tBud | - | 24 | -f |
| 7 | PdCl2(CH3CN)2a | PhCO3tBud | - | 4g | -f |
| 8 | PdCl2(CH3CN)2a | PhCO3tBud | L1a | 24 | 23 |
| 9 | PdCl2(CH3CN)2h | PhCO3tBud | - | 24 | 25 |
| 10 | PdCl2(CH3CN)2a | PhCO3tBud | - | 24i | 25 |
| 11 | PdCl2(CH3CN)2a | F+d,j | - | 24 | 74 |
a
5 mol %.
b
1 equiv.
c
Starting material was recovered.
d
Cu(OAc)2 (5 mol %) was used as a co-oxidant.
e
Conversion: 31%.
f
Decomposition.
g
The reaction was carried out under reflux.
h
10 mol %.
i
2% wt. PT aqueous solution was used as solvent instead of HOAc.
j
N-Fluoro-2,4,6-trimethylpyridinium triflate (1.2 equiv) was used as the oxidant