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On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity. An alternate reaction pathway

revised on 25.02.2021, 05:49 and posted on 25.02.2021, 10:43 by Veejendra Yadav, Dasari L V K Prasad, Arpita Yadav, Maddali L N Rao

The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-tris-carbethoxycyclobutenes to s-trans-trans-1,1,3-tris-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through pathways entailing heterolytic cleavage of the sC3C4 bond rather than the usual four-electron conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl3 catalyzes the reaction of 4-methyl-1,3,3-tris-carbethoxycyclobutene by protonation of one of the two ester groups on C3 and, thereby, weakening the sC3C4 bond to allow its heterolytic SN2 cleavage by the chloride ion. This is followed by cisoidtransoid isomerization and loss of the elements of the halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-tris-carbethoxycyclobutene in CH2Cl2, coordination of the Lewis acid with one of two ester groups on C3 is followed by heterolytic cleavage of the sC3C4 bond. The resultant species subsequently undergoes cisoidtransoid isomerization before losing the Lewis acid to form the products.


Email Address of Submitting Author


Indian Institute of Technology, Kanpur



ORCID For Submitting Author


Declaration of Conflict of Interest

no conflict of interest

Version Notes

This is version 4. In this version, we have changed the title slightly and included 'an alternate reaction pathway' to give due credit to the work of previous researchers. Substantial changes in the text have been made to sharpen focus on our work with critical remarks on previous research. Figures 2, 5 and 6 are new and added to achieve the above objectives.