Protic onium salts-catalyzed synthesis of 5-aryl-2-oxazolidinones from aziridines and CO2 under mild conditions

Abstract

Protic onium salts, e.g. pyridium iodide, proved to be highly efficient and recyclable catalysts for the selective synthesis of 5-aryl-2-oxazolidinones under a CO 2 atmosphere at room temperature, presumably due to aziridine activation assisted by hydrogen bonding on the basis of 1 H NMR and in situ FT IR under CO 2 pressure study.Carbon dioxide is an easily available renewable carbon resource, which has the advantages of being nontoxic, abundant, and economical. 1 The [2 + 3] coupling reaction between CO 2 and aziridines is one of the few commercial routes using CO 2 as a raw material to afford the 5-membered materials (Scheme 1), which are important heterocyclic compounds showing wide applications as intermediates 2a-d and chiral auxiliaries 2e-g in organic synthesis. Therefore, a growing effort has been devoted to developing efficient methodologies for producing oxazolidinones. From the viewpoint of green chemistry, the cycloaddition procedure utilizing CO 2 as a feedstock is more attractive in comparison with those processes including carbonylation of amino alcohols with phosgene, 3a,b CO, 3c and reaction of propargylamine/propargylic alcohol with CO 2 . 3c-g

Recent applications of aziridine ring expansion reactions in heterocyclic synthesis

“…A number of catalysts are known in literature to ease the reaction. Some of these involve quaternary ammonium bromide-functionalized polyethylene glycol, 101 zirconyl chloride, 102 alkali metal halide, 103 Lewis basic ionic liquids, 104 protic onium salt, 105 polyethylene glycolfunctionalized phosphonium salts, 106 DBN, 107 polyethylene glycol functionalized ionic liquids, 108 2,2',2''-terpyridine, 109 and mesoporous zirconium phosphonates. 110 A very few selected examples are described in succeeding paragraphs.…”

Substrate‐Controlled Product Divergence: Conversion of CO2 into Heterocyclic Products

“…Interestingly,w hen epoxy amines are used as substrates only the 5-substituted isomer is formed (10 and 11), and is in contrast to the known (catalytic) couplings between aziridines and CO 2 which often result in the formation of regioisomeric mixtures. [14] Thechemoselectivity for both 12 (54 %) and 13 (75 %) was compromised by the competitive formation of the carbonate product mediated through the conventional mechanism (Scheme 1). [15] To the best of our knowledge,t he trisubstituted carbonates cannot be obtained by using ac onventional approach for catalytic CO 2 /epoxide couplings,t hus demonstrating the added value of this new methodology.…”

Enantioselective Incorporation of CO2: Status and Potential

“…Chirality transfer from enantiopure aziridines provides enantioenriched products. 35,54 This transformation can give two different isomers (Scheme 18), but ionic liquids, 81 NHCs, 82 Cr-salen, 83 and Alsalen/ammonium salt, 35 favour the 5-substituted isomer (if the nitrogen is substituted and R ' = Ph).…”