TABLE 1.
Bromination of p-tolylethyne with hypervalent iodine reagent.
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|---|---|---|---|---|---|---|---|
| Entry | (O) (equiv) | Bromine source (equiv) | Solvent | Temp. (°C) | t (h) | Major product | % Yield (2a:3a:4a:5a:6a) a |
| 1 | PIDA (1.0) | TBAB (1.2) | CH3CN | r.t | 24 | 2a | 76 b (97:1.5:1.5:0:0) |
| 2 | PIDA (2.0) | TBAB (1.2) | CH3CN | r.t | 3 | 2a | 89 c (94:0:0:6:0) |
| 3 | PIDA (1.0) | KBr (2.5) | CH3CN | r.t | 24 | 2a | 44 (87.2:12.8:0:0:0) |
| 4 | PIDA (1.0) | NaBr (2.5) | CH3CN | r.t | 24 | 3a/4a | 66/6 (5.1:84.6:10.3:0:0) |
| 5 | PIDA (2.0) | NaBr (2.5) | CH3CN | r.t | 3 | 3a/4a | 62/28 (0:62:28:10:0) |
| 6 | PIDA (1.0) | NaBr (4.0) | CH3CN | r.t | 5 | 3a/4a | 77 d /8 (0:79.4:8.2:7.2:5.2) |
| 7 | PIDA (1.0) | KBr (2.5) | CH3CN/H2O (1/3) | r.t | 24 | 5a | 48 (1.6:18:3.3:77.1:0) |
| 8 | PIDA (1.0) | NaBr (2.5) | CH3CN/H2O (1/3) | r.t | 24 | 5a | 42 (0:13.7:3.9:82.3:0) |
| 9 | PIDA (2.0) | NaBr (2.5) | CH3CN/H2O (1/3) | r.t | 10 | 5a | 82 (0:2.9:13.5:83.6:0) |
| 10 | PIDA (3.0) | NaBr (3.0) | CH3CN/H2O (1/3) | r.t | 10 | 5a | 97 (0:0:0:97:3) |
a
The yield and the molar ratio of 2a to 3a to 4a to 5a to 6a were determined via 1H NMR, spectroscopy using acetophenone as the internal standard.
b
The isolated yield of 2a in entry 1 was 74%.
c
The isolated yield of 2a in entry 2 was 84%.
d
The isolated yield of 3a in entry 6 was 74%.