Generation of 1,2-bisketenes from ...

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Title Generation of 1,2-bisketenes from cyclobutene-1,2-diones by flash photolysis and ring closure kinetics
Author(s) A. D. Allen, J. D. Colomvakos, F. Diederich, I. Egle, X. Hao, R. Liu, J. Lusztyk, J. Ma, M. A. McAllister, Y. Rubin, K. Sung, T. T. Tidwell, Brian D. Wagner
Journal Journal of the American Chemical Society
Date 1997
Volume 119
Issue 50
Start page 12125
End page 12130
Abstract Abstract: The interconversion of cyclobutene-1,2-diones (1) and 1,2-bisketenes (RC=C=O)2 (2) has been surveyed for different combinations of substituents R = H, Me, t-Bu, Ph, Me3Si, CN, Cl, Br, R1O, alkynyl, and PhS. The bisketenes 2 have been generated by flash photolysis, and the kinetics of their conversion to 1 have been studied by time-resolved infrared and ultraviolet spectroscopy. The rate constants of the ring closure of 2 are correlated by the ketene stabilization parameters (SE) and with calculated barriers. The rate constant of ring closure of the di-tert-butyl bisketene 2g to cyclobutenedione 1g is only 40 times smaller than for the dimethyl analogue, showing a rather modest steric barrier. The quinoketene 2s has a fast rate of ring closure, but not as fast as anticipated on the basis of calculated geometric and thermodynamic factors. A lag in the attainment of aromatic stabilization in the transition structure for ring closure is a possible cause of this diminished reactivity.
DOI 10.1021/ja9722685

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