Organic Chemistry

Torquoselectivity of the Ring-Opening Reaction of 3,3-Dihalosubstituted Cyclobutenes: Lone Pair Repulsion and Cyclic Orbital Interaction

Yuji Naruse Gifu University
,

Abstract

Three major factors determine torquoselectivity, which is the diastereoselectivity in electrocyclic ring-opening reactions to produce E/Z-double bond(s). One is the interaction between the decomposing sCC bond and low-lying vacant orbital(s), such as a p*- or s*-orbital on the substituent, which promotes the reaction, resulting in inward rotation of the substituent. Second, for a substituent with a lone pair(s), repulsive interaction between the decomposing s-bond and the lone pair(s) hinders inward rotation, so that the products of outward rotation should be preferred. Finally, a more strongly donating s-electron-donating group (sEDG) rotates inwardly due to stabilization by phase-continuous cyclic orbital interaction. We compared the latter two interactions, repulsion between the lone pairs on the substituent and stabilization from phase-continuous cyclic orbital interaction, to determine which has a greater effect on the diastereoselectivity. We considered a series of model reactions with halogen substituents, and concluded that the diastereoselectivity is mainly controlled by cyclic orbital interaction.

Version notes

ver. 1.2 prepared on 31 July 2019. modified 25 Dec 2019 in acs format

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