Dataset Information


The Curtius rearrangement of cyclopropyl and cyclopropenoyl azides. A combined theoretical and experimental mechanistic study.

ABSTRACT: A combined experimental and theoretical study addresses the concertedness of the thermal Curtius rearrangement. The kinetics of the Curtius rearrangements of methyl 1-azidocarbonyl cycloprop-2-ene-1-carboxylate and methyl 1-azidocarbonyl cyclopropane-1-carboxylate were studied by (1)H NMR spectroscopy, and there is close agreement between calculated and experimental enthalpies and entropies of activation. Density functional theory (DFT) calculations (B3LYP/6-311+G(d,p)) on these same acyl azides suggest gas phase barriers of 27.8 and 25.1 kcal/mol. By comparison, gas phase activation barriers for the rearrangement of acetyl, pivaloyl, and phenyl azides are 27.6, 27.4, and 30.0 kcal/mol, respectively. The barrier for the concerted Curtius reaction of acetyl azide at the CCSD(T)/6-311+G(d,p) level exhibited a comparable activation energy of 26.3 kcal/mol. Intrinsic reaction coordinate (IRC) analyses suggest that all of the rearrangements occur by a concerted pathway with the concomitant loss of N2. The lower activation energy for the rearrangement of methyl 1-azidocarbonyl cycloprop-2-ene-1-carboxylate relative to methyl 1-azidocarbonyl cyclopropane-1-carboxylate was attributed to a weaker bond between the carbonyl carbon and the three-membered ring in the former compound. Calculations on the rearrangement of cycloprop-2-ene-1-oyl azides do not support pi-stabilization of the transition state by the cyclopropene double bond. A comparison of reaction pathways at the CBS-QB3 level for the Curtius rearrangement versus the loss of N2 to form a nitrene intermediate provides strong evidence that the concerted Curtius rearrangement is the dominant process.


PROVIDER: S-EPMC2653059 | BioStudies | 2008-01-01

REPOSITORIES: biostudies

Similar Datasets

2007-01-01 | S-EPMC2528068 | BioStudies
2008-01-01 | S-EPMC2696164 | BioStudies
2008-01-01 | S-EPMC4222516 | BioStudies
2017-01-01 | S-EPMC5624330 | BioStudies
2009-01-01 | S-EPMC2765507 | BioStudies
2015-01-01 | S-EPMC4415384 | BioStudies
2016-01-01 | S-EPMC5045044 | BioStudies
2020-01-01 | S-EPMC7463175 | BioStudies
2006-01-01 | S-EPMC1637550 | BioStudies
1000-01-01 | S-EPMC5355944 | BioStudies