Table 2. Condition Screening for Cyclization of 6 with 7 Using Various Solvents and Bases at −78 °C.
| entry | solvent | base | result | yield (%) | (R)/(S)a |
|---|---|---|---|---|---|
| 1 | THF | Et3N | oligomerization | ||
| 2 | THF | pyridine | oligomerization | ||
| 3 | THF | DMAP | oligomerization | ||
| 4 | THF | DIPEA | oligomerization | ||
| 5 | DMF | Et3N | oligomerization | ||
| 6 | DMF | pyridine | oligomerization | ||
| 7 | DMF | DMAP | oligomerization | ||
| 8 | DMF | DIPEA | oligomerization | ||
| 9 | CH2Cl2 | Et3N | no reaction | ||
| 10 | CH2Cl2 | pyridine | no reaction | ||
| 11 | CH2Cl2 | DMAP | cyclization | 58 | 88:12 |
| 12 | CH2Cl2 | DIPEA | cyclization | 4 | 8:92 |
a
The (R)/(S) ratio was determined by 31P NMR of reaction crude.