The invention relates to new associations of strong bases, having the following general formula:in which: n and n' are the numbers of mols of each compound, R is an alkyl or aryl radical, M is an alkali metal chosen from amongst lithium, sodium or potassium and Z is a hydride or an inorganic amide, the ratio n/n' being between 0.2 and 50.It is preferred to use bases in which the metal of the alkal