Evaluation of conditions for the Co-catalyzed hydroboration of allene 1a with HBpina.
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|---|---|---|---|---|---|
| Entry | Ligand | Bite angleb | Conversionc (%) | Ratioc (2a/3a) | Yield (%) |
| 1 | PMe3d | — | >99 | 71 : 29 | — |
| 2 | PPh3d | — | >99 | 83 : 17 | — |
| 3 | Dppm | 72 | >99 | 65 : 35 | — |
| 4 | Dppe | 85 | 18 | 76 : 24 | — |
| 5 | Dppp | 91 | 15 | 86 : 14 | — |
| 6 | Dppb | 98 | >99 | 94 : 6 | 78 (2a) |
| 7 | Dpppe | — | >99 | 83 : 17 | — |
| 8 | Dppbz | 83 | >99 | 74 : 26 | — |
| 9 | rac-binap | 92 | 91 | 84 : 16 | — |
| 10 | Dppf | 96 | >99 | 96 : 4 | 81 (2a) |
| 11 | dpephos | 102 | >99 | 61 : 39 | — |
| 12 | Xantphos | 111 | >99 | 6 : 94 | 80 (3a) |
| 13 | Nixantphos | 114 | >99 | 8 : 92 | 76 (3a) |
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a
Conditions: buta-1,2-dien-1-ylbenzene (0.400 mmol), HBpin (0.440 mmol), Co(acac)2 (12 μmol), ligand (12 μmol), toluene (1 mL), room temperature, and 12 h.
b
These values are taken from ref. 11, and the bite angle of dpppe has not been reported.
c
Determined by GC analysis with dodecane as the internal standard.
d
6 mol% of ligand was used.