The reaction of 1,1-dihalo-alkanes with magnesium and magnesium amalgam has been studied. Methylene bromide and iodide yield, under suitable conditions, a stable solution of methylene magnesium halide which easily olefinates aldehydes and ketones affording the corresponding methylenic olefins in good yields. Other alkylidene halides, under the conditions studied, do not give any stable geminal dimagnesium
The sense of the contribution of polarizable allylicaxial bonds to the π–π* Cotton effect of dienes is found to be determined by the chirality of the system which is defined by the direction of the transition moment and direction of the allylic bond.