Table 1. Metal Survey for Salen-Catalyzed Nazarov Cyclization Reaction.
| entry | cat., M, X | additive | time (h) | conv (%)a | erb (dr)c |
|---|---|---|---|---|---|
| 1 | 1a, Co, SbF6 | – | 24 | NR | – |
| 2 | 1b, Co, SbF6 | – | 24 | NR | – |
| 3 | 1c, Cr, SbF6 | – | 9 | >95 | 90:10, 95:5, (2.8:1) |
| 4 | 1c, Cr, SbF6 | 4 Å MS | 4.5 | >95 | 92:8, 96:4 (2.7:1) |
| 5 | 1d, Mn, SbF6 | 4 Å MS | 48 | >95 | 60:40, 73:27 (1.9:1) |
| 6 | 1e, Al, Cl | 4 Å MS/AgSbF6 | 0.5 | >95 | 77:23, 59:41 (1.2:1) |
| 7 | 1f, Cr, Cl | 4 Å MS | 48 | >95 | 83:17, 86:14 (2.2:1) |
| 8 | 1g, Cr, BF4 | 4 Å MS | 8 | >95 | 86:14, 93:7 (2.6:1) |
| 9 | 1h, Cr, AsF6 | 4 Å MS | 8 | >95 | 85:15, 92:8 (1.7:1) |
| 10d | 1i, Cr, BArF | 4 Å MS | 3 | >95 | 91:9, 93:7 (1.8:1) |
| 11 | 1j, Cr, Cl | 4 Å MS/AgB11H6Br6Ce | 0.5 | >95 | 90:10, 95:5 (2.8:1) |
a
Determined using 1H NMR.
b
er of cis and trans diastereomers determined using chiral HPLC.
c
dr determined using 1H NMR.
d
BArF=tetrakis[3,5-bis(trifluoromethyl) phenyl]borate.
e
AgB11H6Br6C = silver hexabromocarborane; NR = no Reaction. See SI for details on tentative assignment of stereochemistry of the product.