Table 1.
Summary of Catalyst Optimization Studiesa
| |||||
|---|---|---|---|---|---|
| entry | 2 | catalyst (mol %) | additived,e | 3/5/6f | product (% yield)g |
| 1 | 2a b | none | none | ≥95% 3a | 3a (93) |
| 2 | 2a b | Rh2(OAc)4 (2) | none | 1:3:0 | 5a (nd) |
| 3 | 2a b | Rh2(TFA)4 (2) | none | 1:12:0 | 5a (nd) |
| 4 | 2a b | Rh2(cap)4 (2) | none | 1:4:0 | 5a (nd) |
| 5 | 2a b | Rh2(esp)2 (2) | none | 1:18:0 | 5a (91) |
| 6 | 2a b | Rh2(esp)2 (1) | none | 1:15:0 | 5a (62) |
| 7 | 2b c | none | none | 2:0:1 | 3b (46) |
| 8 | 2b c | Rh2(esp)2 (1) | none | ≥95% 6 | 6 (92) |
| 9 | 2b c | Rh2(esp)2 (3) | K2CO3 | ≥95% 5b | 5b (88)h |
| 10 | 2b c | none | K2CO3 | 1.3:1:0 | 3b (nd) |
| 11 | 2b c | Rh2(esp)2 (3) | Na2CO3 | 1:10:0 | 5b (nd) |
| 12 | 2b c | Rh2(esp)2 (3) | Cs2CO3 | 1:12:4 | 5b (nd) |
| 13 | 2b c | Rh2(esp)2 (3) | Et3N | 2:4:1 | 5b (nd) |
a
Reactions were carried out on 0.1 mmol scale in a Rayonet using 24 W UV lamps (see the Supporting Information for a description of the reaction setup).
b
Reaction carried out at 35 °C in THF (0.3 M).
c
Reaction carried out at 65 °C in THF (0.1 M).
d
0.5 equiv of additive was used.
e
Reactions containing inorganic bases were heterogeneous.
f
The ratio of products was determined by 1H NMR spectroscopy at 400 MHz from unpurified reaction mixtures.
g
Isolated yield of the indicated major product (nd = not determined).
h
Compound 5b is reactive; isolated yields varied from 62 to 88%.