Chemoselectivity in Coupling of Azides with Thioacids in Solution-Phase and Solvent-Free Conditions

Abstract

Solvent-free rapid coupling of monothiocarboxylic acid with azide affords carboxamide chemoselectively. Triphenyl phosphine included as an additive influences the chemoselectivity, yielding carboxamide and thioamide. Similar variation in the chemoselectivity is observed in the absence and presence of triphenyl phosphine in solution-phase methodology. Rapidity and ecofriendliness of the solvent-free approach to yield the products in just 15 min is noteworthy compared to the solution-phase protocol, which has a long reaction time (1–3 days).

GRAPHICAL ABSTRACT

Keywords:

• Amide
• chemoselectivity
• glycerol bath
• MW irradiation
• solvent-free
• thioamide

ACKNOWLEDGMENTS

The authors thank Intensification of Research in Higher Priority Areas (IRHPA), Department of Science and Technology, for providing the 300-MHz NMR instrument for recording the NMR spectra. S. N., P. S., and M. S. acknowledge their grateful thanks to the University Grants Commission for the sanction of junior research fellowships.

Notes

^a Mixture of azide (1.0 mmol), thioacid (1.0 mmol), and PPh₃ (1.1 mmol) was irradiated with microwaves.

^b Isolated yield.

^c One-pot procedure.

^d Sequential procedure (phozphazene preparation followed by thioacid addition).

^e Identified by ¹H NMR.

^a Ratio in the crude reaction mixture determined by ¹H NMR.

^b One-pot procedure.

^c Sequential procedure (phozphazene preparation followed by thioacid addition).