Reactions with Alkylmagnesium and Alkylaluminium Compounds

Many publications deal with the reactions of oxiranes with the organic compounds of magnesium and aluminium.The review by Boireau et al. ° provides a comprehensive survey of the mechanisms of reaction of the two reagents. 

Studies with symmetric alkylmagnesium compounds indicate that nucleophilic attack occurs on the least-substituted carbon atom of the oxirane (Eqs. 240 and 241). 

The variation in regioselectivity in the case of substituted 1,2-diphenyloxiranes is illustrated in Eq. 244. 

The reaction seen in Eqs. 242-244 are controlled by polar effects. A reaction-kinetics investigation on l-phenyl-2,3-epoxypropane has revealed that the reaction with organomagnesium compounds proceeds in two steps. The first, fast step is a process between the oxirane and the solvated reagent, leading to an equilibrium. 

The second, slow step is attack by a further dialkylmagnesium molecule from the opposite direction. The result is inversion on the reacting carbon atom. Breaking of the C-0 bond of the oxirane is always preceded by the development of a new C-C bond (Eq. 245). °54 

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