Synthesis of Isoxazolo Pyridines by Microwave Assisted Multi-Component Reactions in Water

In our green chemistry section, we learned that one way green chemists make mechanisms greener is by using less toxic solvents. In this study, researchers discovered that water is a better solvent for the production and isolation of isoxazolo pyridines, important biochemical components in the pharmaceutical industry. Isoxazolo pyridines are used in the production of analgeis, anti-inflammatory, anti-bacterial, HIV, and cancer drugs. The reaction was completed without the use of any additional reagents or catalysts.

The reaction was tested in many different solvents, including ethylene glycol, ethanol, acetic acid, and water. Using water as a solvent resulted in the highest percent yield.

entry	solventa	T (°C)	time (min)	yieldb (%)
1	ethyleneglycol	90	10	43
2	ethanol	90	11	54
3	HOAc	90	10	57
4	H2O	90	10	65
5	H2O	100	9	81
6	H2O	110	7	89
7	H2O	120	6	91
8	H2O	130	6	88

Furthermore, the researchers found that when they increased temperature, the yield also increased. However, temperatures higher than 130 °C did not result in an improvement.

The researchers conclude that their new mechanism is simpler than previous mechanisms and is healthier for the environment because it uses water as the solvent, which also reduces waste production.

Source: http://pubs.acs.org/stoken/campaign/acs/full/10.1021/cc800212v