A process of preparing methylaluminium dichloride by (i) reacting by heating a material of the formula R.sub.3Al.sub.2X.sub.3, where R is C.sub.1-C.sub.4 alkyl and X is selected from bromine and iodine with an aluminium-containing material selected from metallic aluminium and a mixture of metallic aluminium and aluminium trichloride in an atmosphere of methyl chloride, with the proviso that when R is methyl and X is iodine, the aluminium-containing material is a mixture of aluminium and aluminium trichloride; and (ii) when the aluminium-containing material is metallic aluminium, adding aluminium trichloride to this reaction mixture and heating, to give a crude reaction product; and (iii) if desired, obtaining methylaluminium dichloride from this crude reaction product. The crude reaction product may be used directly in organic syntheses, such as the cyclisation of .psi.-Georgywood to give .beta.-Georgywood.