The diastereoselectivity of the reduction of 2-t-butylcyclohexanone (1) with diisobutylaluminium-2,6-di-t-butyl-4-methylphenoxide (2) is investigated as a function of the temperature and the conversion. The relevant selection steps are characterized on the basis s of the isoinversion principle. The kinetically controlled formation of the alcoholate intermediates as well as the thermodynamically controlled Meerwein-Ponndorf-Verley type equilibration are recognized as the two selection steps of the reduction.