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Computational studies on the formation of aza‐oxypentadienyl intermediates from alkylidene oxaziridines and keteneimine oxides and their conversion to 1,5‐dihydropyrrolones
Author(s) -
Villar Pedro,
Guillade Lucía,
GonzálezPérez Adán B.,
Lera Angel R.
Publication year - 2019
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.25796
Subject(s) - diradical , chemistry , allene , substituent , oxaziridine , ring (chemistry) , cycloaddition , oxide , transition state , photochemistry , medicinal chemistry , computational chemistry , stereochemistry , catalysis , organic chemistry , excited state , physics , nuclear physics , singlet state
Abstract The rearrangements of alkylidene oxaziridines 1a,b ( a , R = Me; b , R = OMe) and keteneimine oxides 1’a,b to 1,5‐dihydropyrrolones 3a,b have been computationally studied at the UM062X/Def2TZVPP(PCM,TFE)//UM062X/Def2SVP(PCM,TFE) level. The mechanism for conversion of 1a ‐ 3a is predicted to be stepwise, with intermediacy of the acyclic aza‐oxypentadienyl species 4a . The stabilization provided by the nitrogen of the oxaziridine makes the ring opening of 1a to diradical/zwitterionic intermediates 4a more feasible than in the case of the vinyl allene oxide counterparts. The formation of aziridinone 2a from 1a showed competing activation energies but 2a was found to be a thermodynamically less stable species than 3a . When the Me group at N is exchanged by the electron‐donating OMe substituent in 1b , the diradical species and the corresponding transition structures are more stabilized and therefore the aziridinones are not required as intermediates in the conversion of 1b to 3b . Keteneimine oxide 1′ is predicted to directly generate diradical 4 by C‐O ring opening although through a less favored transition state.