Steric Buttressing Changes Torquospecificity in Thermal Cyclobutenone Rearrangements, Providing New Opportunities for 5H-Furanone SynthesisThe authors thank the European Regional Development Fund for their partial support of this work via AI-Chem (InterReg IVa programme 4494/4196) and EPSRC for the equipment grant, reference EP/K039466/1.
Received: 07 April 2017
Accepted after revision: 03 May 2017
13 June 2017 (eFirst)
Thermally induced rearrangements of 4-hydroxycyclobutenones are known to provide clean and reliable access to an array of useful carbocyclic and fused heterocyclic ring systems. Rarely, such reactions have been diverted to an alternative pathway leading to furanone formation. Herein, we show that these switches in the course of the rearrangement occur when a substrate bears a bulky substituent and are due to adverse steric buttressing as the transition state for electrocyclisation is approached. We also show how the reaction provides new opportunities for furanone synthesis and how bulky proton and halogen surrogates can be used to divert classical rearrangement pathways toward furanone formation. Additionally, we show that classical rearrangement pathways can be promoted by the simple expedient of alcohol protection.