Proline-Catalyzed Synthesis of 5-Aryl-2-oxazolidinones from Carbon Dioxide and Aziridines Under Solvent-Free Conditions

Abstract

Natural α-amino acids were proven to be ecofriendly and recyclable catalysts for the carboxylation of aziridines with CO₂ without utilization of any organic solvents or additives. Notably, a series of 5-aryl-2-oxazolidinones were obtained in good yield together with excellent chemo- and regioselectivity under mild conditions using proline as the catalyst. Notably, the catalyst could be recycled more than five times after a simple separation procedure without appreciable loss of catalytic activity. This process represents a promising strategy for homogeneous catalyst recycling.

GRAPHICAL ABSTRACT

Keywords:

• 5-Aryl-2-oxazolidinones
• aziridines
• carbon dioxide
• proline

ACKNOWLEDGMENTS

Financial support from the National Natural Science Foundation of China (Grant Nos. 20421202, 20672054, and 20872073), the 111 Project (B06005), and the Committee of Science and Technology of Tianjin is gratefully acknowledged.

Notes

^a Reaction conditions: amino acids (0.1 mmol, 5 mol% with respect to 1a), 1a (294 mg, 2 mmol), 110 °C, 6 MPa, 1 h.

^b The conversion of 1a and the yield of 2a were determined by GC using biphenyl as an internal standard.

^c Molar ratio of 2a to 3a.

^a Reaction conditions: 1a (294 mg, 2 mmol) and proline (0.1 mmol, 5 mmol% relative to 1a).

^b Determined by GC.

^c The yield of 2a.

^d Molar ratio of 2a to 3a.

^e The first run of the catalyst, proline (20 mmol% with respect to 1a).

^f The second run of the catalyst.

^g The third run of the catalyst.

^h The fourth run of the catalyst.

ⁱ The fifth run of the catalyst.

^j The catalyst loading was 1 mol%.

^k The catalyst loading was 3 mol%.

^a Reaction conditions: proline (0.1 mmol, 5 mol% with respect to the substrate), the substrate (2 mmol), 110 °C, 6 MPa.

^b Determined by GC.

^c Molar ratio of 2 and 3.