Table 3. Oxidative Cyclization of 15cc.
| entry | oxidanta | additiveb | temp (°C) | time (h) | 16:15 (ratio)c | yieldd (%) |
|---|---|---|---|---|---|---|
| 1 | PIFA | BF3·Et2O | –40 | 0.5 | 100:0 | 93 |
| 2 | PIFA | BF3·Et2O | –40 | 4 | 100:0 | 96 |
| 3 | PIFA | BF3·Et2O | +4 | 12 | 100:0 | 90 |
| 4 | PIFA | none | –40 | 4 | 90:10 | 75 |
| 5 | none | BF3·Et2O | –40 | 4 | 0:100 | 0 |
| 6 | DDQ | TFA | rt | 4 | 50:50 | 22 |
| 7 | m-CPBA | TFA | rt | 4 | 80:20 | 38 |
| 8 | none | TFA | rt | 4 | 0:100 | 0 |
a
PIFA = phenyliodine(III) bis(trifluoroacetate); m-CPBA = meta-chloroperbenzoic acid; DDQ = 1,2-dichloro-5,6-dicyanobenzoquinone.
b
TFA = trifluoroacetic acid.
c
16:15 ratio was estimated by 1H NMR analysis methylene of proton integrations (δ4.67 and δ4.32, respectively).
d
Yield refers to isolated yields of pure products after trituration and/or column chromatography; ND = not determined.