The dimerisation of 2-methoxycarbonylbuta-1,3-diene: the importance of paralocalisation energy in assessing diene reactivity

Abstract

The dimerisation and competitive cycloaddition of 2-methoxycarbonylbuta-1,3-diene with electron-rich dienes has been investigated. Experimental results provide evidence that the enthalpy of the π-system significantly influences the energy of the transition state of cycloadditions of this type. This has been corroborated by ab initio calculations. We propose an early reorganisation of the π-electrons in such cycloadditions to explain the influence stated above.