THERMAL ELECTROCYCLIC RING-OPENING OF CYCLOBUTENES: STEREOSELECTIVE ROUTES TO FUNCTIONALISED CONJUGATED (Z,E)- AND (E,E)-2,4-DIENALS

Article abstract of DOI:10.1016/S0040-4020(01)89013-X

The cyclobutenecarbaldehyde 12 undergoes thermal electrocyclic ring-opening at low temperature, producing the (2Z,4E)-hexadienal 13 exclusively.By contrast, unsymmetrical derivatives of cis-3-cyclobutene-1,2-dicarboxylic acid undergo ring-opening at 80-110 deg C with low levels of stereoselectivity, which vary according to the balance of the electronic and, to a lesser extent, the steric nature of the substituents located on the rehybridising carbon atoms.