Table 1. Screening of ansa-Ru(II) Complexes in DKR–ATH of 2-Acetamido-1-indenone (S1)a.
| entry | active Ru(II) cat. | cosolvent | trans/cis | ee (%) (trans) |
|---|---|---|---|---|
| 1 | C1 | – | 65:35 | n.d. |
| 2 | C2 | – | 54:46 | n.d. |
| 3 | C3 | – | 75:25 | n.d. |
| 4 | C4 | – | 84:16 | >99.9 |
| 5 | C4 | DMF | 82:18 | n.d. |
| 6 | C4 | EtOH | 84:16 | n.d. |
| 7 | C4 | EtOAc | 87:13 | n.d. |
| 8 | C4 | (CH2Cl)2 | 90:10 | >99.9 |
| 9 | C4 | toluene | 91:9 | >99.9 |
| 10 | C4 | PhCl | 91:9 (>99)b | >99.9 |
a
ATH of S1 (187 mg, 1.0 mmol) was carried out at 60 °C using the Ru(II) cat. (S/C = 500, 2 μmol) prepared in situ from the corresponding di-μ-chlorido Ru(II) dimer in HCO2H/Et3N 3:2 (1 mL); with a cosolvent (1 mL), less HCO2H/Et3N 3:2 (0.5 mL) was used. Conversion (100% within 3 h) and the trans/cis ratio were determined by 1H NMR, and the ee of the trans-diastereomer was determined by chiral HPLC. n.d. = not determined.
b
After upgrading by trituration with MeCN of the crude (83% total yield).