Table 1. Optimization of the Reaction Conditions for Stereoselective Cu Activation of β,β-Diborylacrylate 1a toward Nucleophilic Allylic Coupling.
| entrya | Cu(I)/ligand | base | T (°C) | NMR yieldb (%) | 2a:3a | 2a (Z:E) |
|---|---|---|---|---|---|---|
| 1 | CuCl/PPh3 | LiOtBu | 60 | >90 | 1:99 | – |
| 2 | iPrCuCl | LiOtBu | 60 | >90 | 1:99 | – |
| 3 | CuCl/PPh3 | Cs2CO3 | 60 | 52 | 89:11 | 99:1 |
| 4 | CuCl/PPh3 | K2CO3 | 60 | 68 | 99:1 | 99:1 |
| 5 | CuCl/PPh3 | K3PO4 | 60 | 93 | 99:1 | 99:1 |
| 6 | CuCl/PPh3 | K3PO4 | 30 | 79 | 99:1 | 99:1 |
a
General conditions: 1,1-diborylalkene (0.2 mmol), 3-bromoprop-1-ene (1.5 equiv), Cu salt (10 mol %), PPh3 (10 mol %), base (2 equiv), THF (4 mL), T, 16 h.
b
Yields determined by NMR with naphthalene as the internal standard.