Table 2.
Effect of different solvents towards the catalyst-free ammonium acetate-mediated synthesis of the Hantzsch dihydropyridine.
| Solvent | Reaction outcomea |
|---|---|
| Hexane | Crude dihydropyridine (58% yield, contaminated with a lot of unidentified byproducts) |
| Acetone | Mixture of unidentified byproducts without any formation of dihydropyridine |
| Dichloromethane | Mixture of unidentified byproducts without any formation of dihydropyridine |
| Chloroform | Mixture of unidentified byproducts with trace amount of dihydropyridine |
| Ethyl acetate | Crude dihydropyridine (54% yield, contaminated with a lot of unidentified byproducts) |
| DMF | Exclusive formation of dihydropyridine (44% yield, remainder starting material) |
| DMSO | Exclusive formation of dihydropyridine (38% yield, remainder starting material) |
| Ethanol | Crude dihydropyridine (60% yield, contaminated with a lot of unidentified byproducts) |
| 1-Propanol | Crude dihydropyridine (39% yield, contaminated with a lot of unidentified byproducts) |
| 2-Propanol | Crude dihydropyridine (36% yield, contaminated with a lot of unidentified byproducts) |
| Water | Exclusive formation of dihydropyridine (89% yield of crystallized product) without any formation of byproduct |
aAll the reactions were done with 4-methylbenzaldehyde : EAA : ammonium acetate = 1 : 2 : 1.3 at the boiling point of the corresponding solvent or at 70°C (whichever is lower) for 1 hr.