Optimization reaction conditions of benzaldehyde and dimedone.
| Entry | Catalyst (mol%) | Solvents | Conditionsa | Times (min)/yieldsb (%) |
|---|---|---|---|---|
| 1 | Catalyst-free | Neat | US (40 kHz), r.t. | 240/trace |
| 2 | Zn(OAc)2 (2 mol%) | Neat | US (40 kHz), r.t. | 120/25 |
| 3 | Zn(OAc)2 (5 mol%) | Neat | US (40 kHz), r.t. | 120/50 |
| 4 | Zn(OAc)2 (10 mol%) | Neat | US (40 kHz), r.t. | 120/69 |
| 5 | Zn(OAc)2 (15 mol%) | Neat | US (40 kHz), r.t. | 120/69 |
| 6 | Zn(OAc)2 (10 mol%) | DCM (2 mL) | US (40 kHz), r.t. | 30/78 |
| 7 | Zn(OAc)2 (10 mol%) | THF (2 mL) | US (40 kHz), r.t. | 30/71 |
| 8 | Zn(OAc)2 (10 mol%) | Toluene (2 mL) | US (40 kHz), r.t. | 30/74 |
| 9 | Zn(OAc)2 (10 mol%) | ACN (2 mL) | US (40 kHz), r.t. | 30/70 |
| 10 | Zn(OAc)2 (10 mol%) | Water (2 mL) | US (40 kHz), r.t. | 30/82 |
| 11 | Zn(OAc)2 (10 mol%) | EtOH (2 mL) | US (40 kHz), r.t. | 30/87 |
| 12 | Zn(OAc)2 (10 mol%) | EtOH (2 mL) | US (40 kHz), 40 °C | 15/90 |
| 13 | Zn(OAc) 2 (10 mol%) | EtOH (2 mL) | US (40 kHz), 60 °C | 15/95 |
| 14 | Zn (OAc)2 (10 mol%) | EtOH (2 mL) | Without US (agitation, r.t.) | 120/trace |
| 15 | Zn(OAc)2 (10 mol%) | EtOH (2 mL) | Without US (agitation, reflux) | 120/35 |
| 16 | Zn(OTf)2 (10 mol%) | EtOH (2 mL) | Without US (agitation, r.t.) | 120/trace |
| 17 | Zn(OTf)2 (10 mol%) | EtOH (2 mL) | US (40 kHz), 60 °C | 120/15 |
a
Reaction conditions: dimedone (2 equiv.), benzaldehyde (1 equiv.).
b
Isolated yields: the yields were calculated after recrystallization in diethyl ether/n-hexane in (6 : 4).