Stereochemical aspects of Michael-type additions to 5-t-butylcyclohex-2-enone

Abstract

5-t-Butylcyclohex-2-enone undergoes Michael-type addition of methanol in the presence of 0·01 M-sodium methoxide at 25°. At equilibrium the mixture comprises: 5-t-butylcyclohex-2-enone (57%), trans-3-methoxy-5-t-butylcyclohexanone (28%), and cis-3-methoxy-5-t-butylcyclohexanone (15%). From a kinetic study it is found that axial attack is favoured over equatorial attack by a factor (k_a/k_e) of 9. The axial adduct predominates over the equatorial adduct in the equilibrium mixture by a factor of 1·9. This is discussed in the light of related examples where relatively electronegative substituents show apparently anomalous axial preferences.

The base-catalysed addition of thiophenol to 5-t-butylcyclohex-2-enone has also been briefly investigated.