No abstract

Aryl- and heteroarylcyclobutenone rearrangements proceed in excellent yield under continuous-flow conditions. The former shows a Hammett correlation with σ(I) providing strong evidence that electrocyclisation is the rate-determining step and has a late transition state. The reaction has been modelled by using DFT and CCSD(T) methods, with the latter giving excellent correlation with the experimental rate constant. A short and efficient total synthesis of cribrostatin 6, an anti-neoplastic and anti-microbial agent, provides a topical demonstration of the value of this method.

Selektivität welcher Art? 4‐Hydroxycyclobutenone wurden in einem photochemischen Strömungsreaktor in 5H‐Furanone umgewandelt. Die Ergebnisse stellen die Vorstellung in Frage, dass diese und die verwandte thermochemische Umlagerung in der elektrocyclischen Ringöffnung zu einem Vinylketenzwischenprodukt torquoselektiv sind. Die Selektivität der photochemischen Reaktion liegt in einer dichotomen Reaktivität der (E)‐ und (Z)‐Vinylketene begründet (siehe Schema).

Diradical intermediates, formed by thermolysis of alkynylcyclobutenones, can display radical, anion, or electrophilic character because of the existence of an orbital isomer with zwitterionic and cyclohexatrienone character. Our realization that water, alcohols, and certain substituents can induce the switch provides new opportunities in synthesis. For example, it can be used to shut down radical pathways and to give access to aryl carbonates and tetrasubstituted quinones.

Diradical intermediates,f ormed by thermolysis of alkynylcyclobutenones,c an displayr adical, anion, or electrophilic character because of the existence of an orbital isomer with zwitterionic and cyclohexatrienone character.O ur realization that water,alcohols,and certain substituents can induce the switch provides new opportunities in synthesis.F or example,i tc an be used to shut down radical pathwaysa nd to give access to aryl carbonates and tetrasubstituted quinones.