Table 1.
Synthesis of the γ-Silylenolether 10
| ||||||||
|---|---|---|---|---|---|---|---|---|
| Entry | Base (equiv.) | R3SiX (equiv.) | Additive (equiv.) | Time (h) | Temp. (°C) | SM:Pa | (γ:α) | Isolated Yield |
| 1 | TEA (1.3) | TBSCl (1.3) | KI (1.3) | 18 | 50 | 17:83 | >99:1 | 17%d |
| 2 | TEA (1.3) | TBSOTf (1.3) | - | 3.5 | 0 to r.t. | - | - | -d |
| 3 b | LHMDS (2) | TBSCl (5) | HMPA (2.5) | 5 | –78 | 60:40 | >99:1 | 15% |
| 4 b | KHMDS (2) | TBSCl (5) | HMPA (2.5) | 0.5 | –78 | <1:99 | 50:50 | 43% |
| 5 b | LDA (2) | TBSCl (5) | HMPA (2.5) | 5 | –78 | 20:80 | >99:1 | 2%d |
| 6 b | LHMDS (2) | TIPSCl (5) | HMPA (2.5) | 5 | –78 | 90:10 | 72:28 | 9% |
| 7 b | LHMDS (2) | TESCl (5) | HMPA (2.5) | 0.5 | –78 | <1:99 | 77:23 | 20% |
| 8 b | LHMDS (2) | DMPSCl (5) | HMPA (2.5) | 3 | –78 | <1:99 | 56:44 | 37% |
| 9 b,c | LHMDS (3) | TBSCl (4) | HMPA (2.5) | 7 | –78 to –20 | 25:75 | >99:1 | 48% |
a
+APCI ratios;
b
After addition of base and HMPA, stir at 0 °C for 1 h;
c
After addition of TBSCl, reaction was let to warm slowly to –20 °C over 5 h;
d
Degradation and dimerization observed during the reaction