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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

preprint
revised on 30.04.2021, 11:03 and posted on 03.05.2021, 05:41 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 s-trans,trans-1,1,3-tris-carbethoxy-4-phenyl-1,3-butadienes, respectively, are discussed to proceed through pathways entailing heterolytic cleavage of the sC3C4 bond rather than the usual conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl3 catalyzes the reaction by protonation of the geminal ester group to weaken sC3C4 bond and allow its SN2 cleavage by chloride ion. This is followed by cisoidtransoid isomerization and loss of the elements of halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-tris-carbethoxycyclobutene in CH2Cl2, coordination of Lewis acid with the geminal ester group 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.

History

Email Address of Submitting Author

vijendra@iitk.ac.in

Institution

Indian Institute of Technology, Kanpur

Country

India

ORCID For Submitting Author

0000-0001-8294-0677

Declaration of Conflict of Interest

no conflict of interest

Version Notes

This is version 5. In this version, we have included critical solvents effects to correlate with selectivity. The clarity in presentation of results has also been improved.

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