A highly efficient and sustainable synthesis of dihydropyrano[2,3-c]pyrazoles using polystyrene-supported p-toluenesulfonic acid as reusable catalyst

Mahendra A Chaudhari,Jitendra B Gujar,Murlidhar S Shingare,Nivrutti R Jogdand,Deepak S Kawade,George Weaver

doi:10.1080/23312009.2015.1063830

Abstract

AbstractA simple, expedient, and ecofriendly protocol for the one-pot synthesis of dihydropyrano[2,3-c]pyrazole derivatives using polystyrene-supported p-toluenesulfonic acid as a highly active and reusable heterogeneous catalyst in water has been developed. The core advantages of the present protocol are excellent yields, mild reaction conditions, broad substrate scope, and easy work-up procedure. This new protocol exemplifies the operationally simple synthesis of dihydropyrano[2,3-c]pyrazoles in a time-efficient and cost-effective manner.

Highlights

The heterocyclic pyranopyrazole motif is a privileged pharmacophore scaffold found in many biologically active compounds of diverse origins, from natural products to synthetic sources
It was observed that p-toluenesulfonic acid (PTSA), triethylamine (TEA), and diisopropylethylamine (DIEA) gave the desired product albeit in low yields, i.e., 58, 49, 35% respectively (Table 1, entry 4–6)
PS-PTSA was chosen as catalyst for the synthesis of dihydropyrano[2,3-c]pyrazoles, despite the fact that we compare polystyrene-supported acid and base catalyst at every step

Summary

Introduction

The heterocyclic pyranopyrazole motif is a privileged pharmacophore scaffold found in many biologically active compounds of diverse origins, from natural products to synthetic sources. The previously reported methods include catalysts, such as heteropolyacids, cocamidopropyl betaine, triethyl ammonium bromide, piperazine, piperidine, polyphosphoric acid supported on Ni0.5Zn0.5Fe2O4 nanoparticles, disulphonic acid imidazolium chloroaluminate, sodium benzoate, and per-6-aminoβ-cyclodextrin (Chavan, Babar, Hoval, & Bandgar, 2011; Kanagaraj & Pitchumani, 2010; Kiyani, Samimi, Ghorbani, & Esmaieli, 2013; Kumar et al, 2013; Moeinpour & Khojastehnezhad, 2014; Moosavi-Zare et al, 2013; Peng, Song, & Dou, 2006; Tamaddon & Alizadeh, 2014; Vasuki & Kumaravel, 2008) Most of these synthetic protocols reported suffer from high catalyst loading, prolonged reaction time, harsh reaction conditions, poor recyclability, and low yields. Pyrazoles using polystyrene-supported p-toluenesulfonic acid due to its many practical benefits which attracted our interest

Results and discussion

Conclusion

Experimental

Spectral data for representative compound