with acetic anhydride or tosyl chloride and methyl iodide give imidazolinium salts that serve as models of N5,N10-(CH+)-tetrahydrofolate (THF) coenzymes (7a, b and 18a, b). Reduction of the latter salts with sodium borohydride or reaction with anions (R−) give the corresponding 5,10-[CH(H,R)]-THF models. Mono- and bifunctional nucleophiles react with 18a, b to yield carbon-transfer products 6-Alkylamino-1