Table 2.
Borylations of 3-substituted thiophenes.a
| Entry | Substrate | Conditions | 5-Borylated Product | 3-Borylated Product | a:b b | Yield %c |
|---|---|---|---|---|---|---|
| 1 |
|
0.5 equiv HBPin, 1 h |
|
|
1:1.13 | 54d |
| 2 |
|
0.5 equiv HBPin, 1 h |
|
|
3.5:1 | 66d |
| 3 |
|
0.5 equiv HBPin, 1 h |
|
|
8.9:1 | 72d |
| 4 |
|
0.5 equiv HBPin, 1 h |
|
|
8.9:1 | 67d |
| 5 |
|
1.2 equiv HBPin, 15 min |
|
-- | >99:1 | 82 |
| 6 |
|
1.2 equiv HBPin, 1 h |
|
-- | >99:1 | 95 |
| 7 |
|
1.2 equiv HBPin, 30 min |
|
-- | >99:1 | 79 |
| 8 |  |
0.9 equiv HBPin, 1 h |
|
|
>32:1 | 74d |
a
Reactions were carried out with 3 mol% or pregenerated Ir catalyst in n-hexane at room temperature with 1.5–2.0 equiv HBPin. For details see the Experimental Section.
b
Isomer ratios were determined by GC analysis of the crude reaction mixture.
c
Yields are reported for isolated products and are based on starting thiophene unless otherwise noted. Isomers were not separated.
d
Yield based on HBPin.