A theoretical study on the metal-free triazole formation through tandem [3+2] cycloaddition/retro-Diels-Alder reaction of benzyl azide and oxanorbornadienedicarboxylate

A density functional theory study was performed on the mechanism and site selectivity of a domino [3 + 2] cycloaddition/retro-Diels-Alder reaction between benzyl azide and 7-oxabicyclo [2.2.1]hepta-2,5-diene-2,3-dicarboxylate (oxanorbornadienedicarboxylate) which provide a stable 1,2,3-triazole and the results were compared with the click reaction between benzyl azide and dimethyl acetylenedicarboxylate (DMAD) with similar triazole product. Parr functions analysis, hard and soft acids and bases (HSAB) principle and potential energy surface analysis were utilized for studying the site selectivity of this reaction, and the results are consistent with the experimental observations. The molecular mechanisms of these reactions were established by electron localization function (ELF) and noncovalent interactions (NCI) topological analysis. ELF topological patterns indicated a two-stage one-step mechanism for the 32CA reaction and NCI analysis displayed the noncovalent interactions which are responsible for the preferred path. (C) 2020 Elsevier Inc. All rights reserved.