Vitamin B12 in the form of its coenzyme acts as cofactor for a remarkable series of enzymatic transformations. Three of these: Beta- methylaspartate mutase, methylmalonyl-CoA mutase and methylitaconate mutase are of particular interest because they involve a carbon-skeleton rearrangement for which there is no analogy in organic chemistry. Here we present partial, experimental models for two of these reactions. The model reactions are the thermal rearrangements of methyl 3,3- dimethylglycidate to methyl levulinate and methyl 3-methly-3- carbomethoxyglycidate to dimethyl alpha-ketoglutarate. Also presented is a general scheme which offers an explanation of the coenzyme-B12 catalyzed reaction in a biochemical context. It is proposed to probe the role of these and other possible intermediates in the enzymatic reactions. The role of cobalt will be explored further. Novel thermal rearrangements of epoxides, aziridines, cyclopropanes, enol ethers and enamines will be studied. A new, apparent 1,3-sigmatropic shift in an enol ether system will be examined more closely with the aid of double-labelling and optical activity. It is intended to develop a preparatively unexplored and potentially extremely mild method for making epoxides by photolysis of nitrous oxide in the presence of olefins. New substrates for the coenzyme-B12 dependent enzymes will be sought. A search will be made for a metal- catalyzed ketone to epoxide rearragement. Finally, new mild enzyme model reactions will be sought.