Theoretical Predictions of Substituent Effects on the Thermal Electrocyclic Ring Openings of Cyclobutenones

Abstract

The transition structures for the electrocyclic ring openings of a variety of substituted cyclobutenones were located with ab initio molecular orbital theory. The effects of substituents on the stereochemistries and activation energies of the electrocyclic ring openings are predicted to be similar to those in cyclobutene.

Exploring Diradical Chemistry: A Carbon‐Centered Radical May Act as either an Anion or Electrophile through an Orbital Isomer

“…[17,18] In line with the work of others, [19] our analysis gave a DE value for the diradical 13 A and it was 4.1 kcal mol À1 lower than that for the zwitterionic isomer 13 B (see Figure 1a nd the Supporting Information). To test that hypothesis,w e modelled the reaction using DFT calculations [at the UB3LYP/6-311G(d,p) level].…”

Computational Study of Rh-Catalyzed Carboacylation of Olefins: Ligand-Promoted Rhodacycle Isomerization Enables Regioselective C–C Bond Functionalization of Benzocyclobutenones

“…Due to the loss of aromaticity, the benzocyclobutenone electrocyclic ring opening is much less favorable than the ring opening of cyclobutenones. 29 The ring opening of the rhodium-bound complex 3 is even less favorable (green pathway in Figure 3) in terms of activation free energies due to unfavorable entropic effects. Thus, the electrocyclic ring opening mechanisms are ruled out.…”

Cycloaddition and Electrocyclic Reactions of Vinylketenes, Allenylketenes, and Alkynylketenes

“…This zwitterion either undergoes direct ring closure to form β-lactam cis-10, or isomerizes by bond rotation to afford zwitterion 11, which undergoes ring closure to β-lactam trans-10 (Scheme 13). As noted in the Scope and Limitations section (Scheme 30), electronic effects on the sense of rotation (torquoselectivity) in the ring opening and closing of cyclobutenones have been considered, 39 and this concept has been extended to the electrocyclization of the zwitterionic intermediates in the Staudinger β-lactam synthesis. Later work has, however, suggested that the theory of torquoselectivity cannot reliably be used to predict the stereochemical course of β-lactam formation.…”

“…The torquoselectivity in the thermal ring opening of cyclobutenones 24 has been examined by computational means and proposed to occur with preferential outward rotation of electron donating groups (Scheme 30). 39 The torquoselectivity is usually not high, and the cyclobutenone opening and closing is reversible, so a steady-state concentration of the (Z)-vinylketene will also be present and may lead to observed products. O • O…”