On the generation of oxirene and dimethyloxirene by retro-DielsAlder reactions, and reactions of dimethyloxirene: a computational study

The isomerization of oxirene (oxacyclopropene) (1) to ketene, dimethyloxirene (7) to dimethylketene via the oxo carbene ("ketocarbene"), and the retro-Diels–Alder extrusion of oxirene and dimethyloxirene from their formal adducts (9 and 24, respectively) with benzene were studied computationally. All species were optimized at the MP2(fc)/6–31G(df,p) level; the species involving 1 were also subjected to MP2(fc)/6–31G(df,p) frequency and single-point CCSD(T)/6–31G(df,p) calculations. At the CCSD(T)/6–31G(df,p)//MP2(fc)/6–31G(df,p) level 1 isomerized to ketene in one step with a barrier of 2.8 kJ mol–1 and a reaction energy of –320.6 kJ mol–1. The extrusion of 1 from 9 had a late transition state and activation and reaction energies of 264.2 and 214.2 kJ mol–1, respectively, cf. cyclopropene extrusion from its adduct (192.3 and 95.9 kJ mol–1), indicating an antiaromatic destabilization energy of 214.2 – 95.9 = 118 kJ mol–1 for 1. The carbene 8 from ring-opening of 7 lay 10.9 kJ mol–1 above 7 (CCSD(T)/6–31G(df,p)//MP2(fc)/6–31G(df,p)), but the transition state could not be found; 8 isomerized to dimethylketene (252.7 kJ mol–1 below 7) with a barrier of 16.4 kJ mol–1, and to s-(Z)- and s-(E)-butenone with barriers of 28.5 and 35.4 kJ mol–1, respectively. The UV (TDDFT, B3P86/6–311++G**//MP2(fc)/6–31G(df,p)) spectra of 1 and 7 were calculated. Discrepancies were seen between the calculated IR spectra of 7 (bis(trifluoromethyl)oxirene) and perfluoro ethyl methyloxirene, and those attributed to these species in earlier matrix-isolation work. Key words: oxirene, dimethyloxirene, ab initio, retro-Diels–Alder, Diels–Alder.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.