RESEARCH ARTICLE The mechanism of the reaction between an aziridine and carbon dioxide with no added catalyst Chau Phung 1 | Dean J. Tantillo 2 | Jason E. Hein 3 | Allan R. Pinhas 1 1 Department of Chemistry, University of Cincinnati, Cincinnati, OH, USA 2 Department of Chemistry, University of California‐Davis, Davis, CA, USA 3 Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada Correspondence Allan R. Pinhas, Department of Chemistry, University of Cincinnati, Cincinnati, OH, USA Email: djtantillo@ucdavis.edu; jhein@chem. ubc.ca; allan.pinhas@uc.edu Abstract The mechanism of the reaction at room temperature between an unactivated 2‐alkyl aziridine and carbon dioxide to generate the corresponding oxazolidinone in glass has been studied. Theoretical calculations suggest that this reaction should not pro- ceed at room temperature in the absence of a catalyst. In cases where a reaction was observed, kinetic studies show that the reaction displays a zero‐order dependence with respect to aziridine, indicating that free aziridine is not involved in the rate‐ determining step. An ammonium salt generated in situ acts as a catalyst. The amount of this catalyst is diminutive, which prevented spectroscopic identification, and it is not readily removed from the starting material using chromatography. KEYWORDS aziridine, calculations, carbon dioxide, catalysis, kinetics 1 | INTRODUCTION According to recent reviews, in comparison to activated aziridines, few papers have been published on the chemistry of readily available unactivated N‐alkyl aziridines. [1] One reaction of an N‐alkyl aziridine is the insertion of carbon dioxide into a C–N bond to generate an oxazolidinone, which is an important class of compounds used as chiral auxiliaries, as metal ligands, and as pharmaceuticals (specifically as antibiotics). [2–4] Although carbon dioxide is abundant, renewable, nonflamma- ble, and inexpensive, due to its stability, [5,6] using this resource as a synthetic feedstock typically requires difficult to synthesize catalysts, high pressures (typically over 100 atm), and/or high temperatures (typically over 100°C). [7–10] In addition, most of these reactions only work with mono‐aryl substituted aziridines, such as 4, and fail with alkyl‐substituted compounds, such as 1. For the past several years, we have been investigating the reactions shown in Scheme 1 in which both alkyl‐ and aryl‐ substituted unactivated aziridines (1 and 4) are converted to the corresponding oxazolidinones at low pressure and tempera- ture using a salt, such as LiI or NH 4 I, as a catalyst in THF. [11–14] When a control experiment using no catalyst in THF was allowed to go for an extended period (12 vs 4 h or less when a salt is used) at room temperature, the reaction of compound 1 (Scheme 1, R = PhCH 2 and alkyl = CH 3 ) with CO 2 (3 atm) gave oxazolidinones 2+3, albeit in very low yield. Because the aziridine is an oil and CO 2 is a gas, the reaction was attempted with no solvent. When aziridine 1 was stirred, with no catalyst or solvent, under a CO 2 pressure of 3 atm for 12 hours, the yield of oxazolidinones 2+3 increased to 37% from the 7% in THF. Increasing the applied pressure of CO 2 to 4 atm did not have a significant impact on the observed yield, giving products 2+3 in approximately 40%. Under all conditions, compound 2 is the major isomer, typically being formed with a product ratio of about 13:1. At approximately the same time, it was reported in the literature that N‐alkyl‐2‐aryl aziridines (4) will generate the corre- sponding oxazolidinone (5) with no catalyst at high tempera- ture and pressure. [15] These results led to an effort to discover the mechanism of the conversion of an aziridine with CO 2 into an oxazolidinone using no catalyst. 2 | RESULTS AND DISCUSSION 2.1 | Possible mechanisms On the basis of literature precedent, we initially proposed two possible mechanisms for these transformations, both Received: 27 April 2017 Revised: 2 June 2017 Accepted: 5 June 2017 DOI: 10.1002/poc.3735 J Phys Org Chem. 2017;e3735. https://doi.org/10.1002/poc.3735 Copyright © 2017 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/poc 1 of 7