Table 1. Condition Optimizationa.
entry | H2O (equiv) | acid (equiv) | solvent | 2a (%) |
---|---|---|---|---|
1 | 20 | CF3COOH | MeCN | 26 |
2 | 20 | CH3COOH | MeCN | 33 |
3 | 20 | CCl3COOH | MeCN | 55 |
4 | 20 | CCl3COOH | DCM | NR |
5 | 20 | CCl3COOH | THF | NR |
6 | 20 | CCl3COOH | acetone | 79 |
7 | 40 | CCl3COOH | acetone | 68 |
8 | 10 | CCl3COOH | acetone | 84 |
9 | CCl3COOH | acetone | 96(80)b | |
10c | CCl3COOH | acetone | 83 | |
11d | CCl3COOH | acetone | 76 | |
12 | acetone | 48 | ||
13e | CCl3COOH | acetone | NR | |
14f | CCl3COOH | acetone | NR | |
15g | CCl3COOH | acetone | NR |
General conditions: DPE (0.4 mmol), UO2(NO3)2·6H2O (4 mol %), acid (2 equiv), solvent (2 mL), N2, RT, 48 h, blue light (460 nm), 1H NMR yields with CH2Br2 as the internal standard.
Isolated yields.
Acid (1 equiv).
Acid (4 equiv).
Without light.
Without UO2(NO3)2·6H2O.
Ru(bpy)3Cl2·6H2O, Eosin Y, or Ir(ppy)2(dtbbpy)·BF4 take place of UO2(NO3)2·6H2O. NR = No reaction.