Bulletin of the Chemical Society of Japan p. 1943 - 1950 (1989)
Update date:2022-08-11
Topics:
Yasuda, Masahide
Yoshida, Kouhei
Shima, Kensuke
Pac, Chyongjin
Yanagida, Shozo
Regiochemistry and rectivities in the thermal ring-splitting reactions of diarylcyclobutanes (1-5) have been studied and shown to depend on the stable conformations and rotational mobilities of the aryl substituents.The reactions of 1 and 2 result in a regiospecific symmetric cleavage to give indene or styrene along with significant isomerization of 2 to 3.In the cases of 3-5 both the symmetric and unsymmetric cleavages competitively occur with decreasing symmetric-to-unsymmetric ratios with an increase in methyl substitution.The olefin products from 4 are mixtures of cis- and trans-2-butene, cis- and trans-β-methylstyrene, and trans-stilbene.Thermochemical analyses combined with product analyses indicate that the symetric cleavage of 1 and the unsymmetric cleavage of 3 proceed with a concerted mechanism, whereas 1,4-biradicals are involved in the other reactions.Structure-reactivity relationships of the present reactions are discussed in terms of mixing of the ?* character in a bonding MO by specific ?-?* interactions, depending on the conformational situations of the aryl groups and in terms of the steric effects which destabilize 1,4-biradicals as well as transition states of the biradical fragmentation to the olefins.
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Doi:10.1021/ja01233a018
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(1960)