Squaramide-Quaternary Ammonium Salt as an Effective Binary Organocatalytic System for Oxazolidinone Synthesis from Isocyanates and Epoxides

Efficient methods for the synthesis of chiral 2-oxazolidinones as pharmaceutical building blocks

Although the wide variety of heterocyclic compounds is common knowledge, chiral 2-oxazolidinones are recognized as some of the most important heterocycles in medicinal chemistry. Many important pharmaceutical molecules have been constructed based on the chiral 2-oxazolidinone backbone. Therefore, the development of even more efficient catalytic methods for the synthesis of chiral 2-oxazolidinones remains a very important pursuit in the field of synthetic organic chemistry. This review summarizes the coupling reactions of epoxides and isocyanates for the preparation of 2-oxazolidinones. Both metal catalysts and organocatalysts promote these reactions. Optically pure 2-oxazolidinones are prepared from optically pure epoxide substrates via these catalytic methods. A synthetic example of a commercially available pharmaceutical compound utilizing this method is also introduced.

Amine-catalyzed site- and stereo-selective coupling of epoxy amines and carbon dioxide to construct oxazolidinones

NEt3 catalyzed the cycloaddition of epoxy amine and CO2, which generated oxazolidinones. Reactions of chiral epoxy amine achieved 100% configuration inversion, enabling the synthesis of linezolid. DFT studies show that NEt3 acted as a nucleophile.

Microwave-Assisted Electrostatically Enhanced Phenol-Catalyzed Synthesis of Oxazolidinones

An electrostatically enhanced phenol is utilized as a straightforward, sustainable, and potent one-component organocatalyst for the atom-economic transformation of epoxides to oxazolidinones under microwave irradiation. Integrating a positively charged center into phenols over a modular one-step preparation gives rise to a bifunctional system with improved acidity and activity, competent in rapid assembly of epoxides and isocyanates under microwave irradiation in a short reaction time (20-60 min). A careful assessment of the efficacy of various positively charged phenols and anilines and the impact of several factors, such as catalyst loading, temperature, and the kind of nucleophile, on catalytic reactivity were examined. Under neat conditions, this one-component catalytic platform was exploited to prepare more than 40 examples of oxazolidinones from a variety of aryl- and alkyl-substituted epoxides and isocyanates within minutes, where up to 96% yield and high degree of selectivity were attained. DFT calculations to achieve reaction barriers for different catalytic routes were conducted to provide mechanistic understanding and corroborated the experimental findings in which concurrent epoxide ring-opening and isocyanate incorporation were proposed.