Recent developments on ultrasound-assisted one-pot multicomponent synthesis of biologically relevant heterocycles

Heterocycles are the backbone of organic compounds. Specially, N- &O-containing heterocycles represent privileged structural subunits well distributed in naturally occurring compounds with immense biological activities. Multicomponent reactions (MCRs) are becoming valuable tool for synthesizing structurally diverse molecular entities. On the other hand, the last decade has seen a tremendous outburst in modifying chemical processes to make them sustainable for the betterment of our environment. The application of ultrasound in organic synthesis is fulfilling some of the goals of 'green and sustainable chemistry' as it has some advantages over the traditional thermal methods in terms of reaction rates, yields, purity of the products, product selectivity, etc. Therefore the synthesis of biologically relevant heterocycles using one-pot multi-component technique coupled with the application of ultrasound is one of the thrusting areas in the 21st Century among the organic chemists. The present review deals with the "up to date" developments on ultrasound assisted one-pot multi-component synthesis of biologically relevant heterocycles reported so far.

N-Sulfonic acid poly(4-vinylpyridinium) hydrogen sulfate as an efficient and reusable solid acid catalyst for one-pot synthesis of xanthene derivatives in dry media under ultrasound irradiation

N-Sulfonic acid poly(4-vinylpyridinium) hydrogen sulfate catalyzed efficiently the synthesis of xanthene derivatives under ultrasonic irradiation at room temperature, which has prompted various concerns involving cost and environmental persistence. This methodology shows the effect of presence of anion hydrogen sulfate as an important and effective factor on the promotion of the one-pot multi-components and condensation reactions. The catalyst can be recovered by simple filtration and used for several times without a significant loss of catalytic activity.