TABLE 3.
Selective bromination of terminal alkynes with hypervalent iodine reagents.
| ||||
|---|---|---|---|---|
| Entry | Alkyne | Method a | Major product | % Yield (2a:3a:4a:5a:6a) b |
| 1 | R = p-to1yl | A | 2a | 89 (94:0:0:6:0) |
| 2 | B | 3a/4a | 77/8 (0:83.7:8.7:7.6:0) | |
| 3 | C | 5a | 97 (0:0:0:96.6:3.4) | |
| 4 | D | 6a | 93 (0:0:0:6.4:93.6) | |
| 5 | R = m-to1yl | A | 2b | 95 (100:0:0:0:0) |
| 6 | B | 3b/4b | 58/3 (0:87.9:4.5:7.6:0) | |
| 7 | C | 5b | 73 (0:0:0:81.1:18.9) | |
| 8 | D | 6b | 64 (0:0:0:0:100) | |
| 9 | R = Ph | A | 2c | 84 (100:0:0:0:0) |
| 10 | B | 3c/4c | 45/3 (17.4:52.4:3.5:17.4:9.3) | |
| 11 | C | 5c | 72 (0:0:0:92.3:7.7) | |
| 12 | D | 6c | 64 (0:0:0:0:100) | |
| 13 | R = p-MeO-C6H4 | A | 2d | 69 (75.8:24.2:0:0:0) c |
| 14 | B | 3d/4d | 82/3 (10.5:86.3:3.2:0:0) d | |
| 15 | C | 5d | 87 (0:0:0:100:0) | |
| 16 | D | 6d | trace | |
| 17 | R = p-MeOCO-C6H4 | A | 2e | 88 (100:0:0:0:0) |
| 18 | B | 3e/4e | 56/8 (20:70:10:0:0) | |
| 19 | C | 5e | 9 (0:8.3:53.6:10.7:27.4) | |
| 20 | D | 6e | 15 (0:64.9:14.9:0:20.2) | |
| 21 | R = p-F-C6H4 | A | 2f | 98 (100:0:0:0:0) |
| 22 | B | 3f/4f | 55/6 (0:79.7:8.7:0:11.6) | |
| 23 | C | 5f | 78 (0:3.1:0:80.4:16.5) | |
| 24 | D | 6f | 53 (0:0:0:8.6:91.4) | |
| 25 | R = p-Cl-C6H4 | A | 2g | 99 (100:0:0:0:0) |
| 26 | B | 3g/4g | 40/4 (49.4:46:4.6:0:0) | |
| 27 | C | 5g | 69 (0:0:0:82.1:17.9) | |
| 28 | D | 6g | 31 (0:12.1:34.5:0:53.4) | |
| 29 | R = p-Br-C6H4 | A | 2h | 78 (100:0:0:0:0) |
| 30 | B | 3h/4h | 42/4 (14.8:77.8:7.4:0:0) | |
| 31 | C | 5h | 54 (21.3:4.3:0:57.4:17) | |
| 32 | D | 6h | 22 (32.2:6.2:20.8:0:33.8) | |
| 33 | R = p-CF3-C6H4 | A | 2i | 99 (100:0:0:0:0) |
| 34 | B | 3i/4i | 54/11 (16.7:69.2:14.1:0:0) | |
| 35 | C | 5i | 9 (0:11.1:65.4:11.1:12.4) | |
| 36 | D | 6i | 14 (0:12.2:71.5:2:14.3) | |
| 37 | R = p-N O 2-C6H4 | A | 2j | 85 (97.7:2.3:0:0:0) |
| 38 | B | 3j/4j | 39/10 (7.5:73.6:18.9:0:0) | |
| 39 | C | 5j | 2 (0:7.5:62.7:3:26.8) | |
| 40 | D | 6j | 18 (53.8:12.5:15.4:0:18.3) | |
| 41 | R = CH2CH2OH | A | 2k | 56 (100:0:0:0:0) |
| 42 | B | 3k/4k | trace | |
| 43 | C | 5k | trace | |
| 44 | D | 6k | 61 (0:10.4:2.6:7.8:79.2) | |
Method A: Alkyne (1.0 equiv), TBAB (1.2 equiv), and PIDA (2.0 equiv) in CH3CN, r. t, 1–3 h. Method B: Alkyne (1.0 equiv), NaBr (4.0 equiv), and PIDA (1.0 equiv) in CH3CN, r. t, 1–5 h. Method C: Alkyne (1.0 equiv), NaBr (3.0 equiv), and PIDA (3.0 equiv) in CH3CN/H2O (1/3), r. t, 10 h. Method D: (i) Alkyne (1.0 equiv), NaBr (6.0 equiv), and PIDA (4.0 equiv) in CH3CN, r. t, 3 h; (ii) NaBr (3.0 equiv), and PIDA (1.0 equiv), r. t, 3 h.
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.
The isolated yield of 2days in entry 13 was 73%.
The isolated yield of 3days in entry 14 was 86%.