Table 1.
| |||||
---|---|---|---|---|---|
Entry | X+ Sourcea | Solvent | Additive | °C | % eeb |
1 | NBS | CH2Cl2 | - | RT | 22 |
2 | NBS | CH2Cl2 | - | −20 | 14 |
3 | NBS | CHCl3 | - | RT | 35 |
4 | NCS | CH2Cl2 | - | RT | 39 |
5 | NCS | CHCl3 | - | RT | 65 |
6 | NCS | CHCl3 | - | −40 | NRc |
7 | DCDMH | CHCl3 | - | RT | 71 |
8 | DCDMH | CHCl3 | - | −40 | 83 |
9 | DCDMH | CHCl3 | PhCO2H | −40 | 86 |
10 | DCDMH | CHCl3/Hex (1:1) | - | −40 | 86 |
11 | DCDMH | CHCl3/Hex (1:1) | PhCO2H | −40 | 89 |
12 | DCDPH | CHCl3/Hex (1:1) | PhCO2H | −40 | 89 |
X = Br for entries 1-3, and Cl for entries 4-12.
as judged by chiral HPLC or GC analysis.
NR = no reaction after 3 hours.