Table 1.
Selected optimization experiments in the enantioselective iridium-catalyzed reductive coupling of oxetanone 1a with allyl acetate 2a to form oxetanol 3a.a
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|---|---|---|---|---|---|
| Entry | Base | (S)-Ligand | X | Additive | 3a (Yield, ee) |
| 1 | Cs2CO3 (20 mol%) | I | CN | --- | 44%, 98% |
| 2 | Cs2CO3 (20 mol%) | II | CN | --- | 37%, 98% |
| 3 | Cs2CO3 (20 mol%) | III | CN | --- | 42%, 99% |
| 4 | Cs2CO3 (20 mol%) | IV | CN | --- | 44%, 99% |
| 5 | Cs2CO3 (20 mol%) | V | CN | --- | 40%, 97% |
| 6 | Cs2CO3 (20 mol%) | VI | CN | --- | 46%, 99% |
| 7 | Cs2CO3 (20 mol%) | VII | CN | --- | 61%, 99% |
| 8 | Cs2CO3 (20 mol%) | VII | OMe | --- | 20%, 98% |
| 9 | Cs2CO3 (20 mol%) | VII | NO2 | --- | 64%, 98% |
| 10 | Cs2CO3 (100 mol%) | VII | NO2 | --- | 23%, 98% |
| 11 | K2CO3 (20 mol%) | VII | NO2 | --- | 30%, 99% |
| 12 | K2CO3 (100 mol%) | VII | NO2 | --- | 79%, 99% |
| ➡13 | K2CO3 (100 mol%) | VII | NO 2 | 3,4-(NO2)2BzOH | 96%, 99% |
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Yields of material isolated by silica gel chromatography. Enantioselectivities were determined by chiral stationary phase HPLC analysis. See Supporting Information for further details.