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The Vinylketene‐Acylallene Rearrangement: Theory and Experiment
Author(s) -
Bibas Hervé,
Wong Ming Wah,
Wentrup Curt
Publication year - 1997
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19970030212
Subject(s) - chemistry , ketene , substituent , alkoxy group , lone pair , homo/lumo , medicinal chemistry , thermal decomposition , flash photolysis , photochemistry , matrix isolation , chlorine , allene , infrared spectroscopy , reaction rate constant , molecule , catalysis , organic chemistry , kinetics , alkyl , physics , quantum mechanics
Alkoxyvinylketenes 4 are generated by flash vacuum thermolysis (FVT) or photolysis of 3‐alkoxycyclobutenones 3 . The thermal interconversion of 4 and allene carboxylic acid esters 5 under FVT conditions is demonstrated by Ar matrix FTIR spectroscopy. In addition, ethoxy‐vinylketene 4b undergoes thermal elimination of ethene with formation of s‐cis‐ and s‐trans‐ acetylketene (8) . An analogous aminovinylketene‐to‐allenecarbox‐amide conversion is observed on FVT of 3‐dimethylaminocyclobutenone 3c . A facile 1, 3‐chlorine migration in 2, 3‐buta‐dienoyl chloride (5d) is also reported. Consistent with the experimental observations, 1, 3‐methoxy, 1, 3‐chloro, and 1, 3‐dimethylamino migrations in vinylketene are calculated (G2(MP2, SVP) level) to have moderate barriers of 169, 157, and 129 kJ mol −1 , respectively, significantly less than the corresponding 1, 3‐H shift barrier (273 kJ mol −1 ). The stabilization of the four‐center transition structures is rationalized in terms of the donor‐acceptor interaction between the lone pair electrons of the migrating donor substituent and the vacant central carbon p orbital of the ketene LUMO. The predicted migratory aptitude in the series of substituted vinylketenes, R‐C(CH 2 )‐CHCO, is in the order N(CH 3 ) 2 >SCH 3 >SH>Cl>NH 2 >OCH 3 >OH>F>H>CH 3 , and correlates well with the electron‐donating ability of the R group.