Condensation of 2-methyl-4-amino-5-aminomethylpyrimidine (I), carbon disulfide, and methyl α-chloro-γ-ethoxypropyl ketone (II), in the presence of ammonia, results in the initial formation of α-aceto-γ-ethoxypropyl N-[2-methyl-4-aminopyrimidyl-(5)]-methyl-dithiocarbamate (VIII) which is very labile and immediately undergoes intramole-cular rearrangement to form its isomer, 2-methyl-2-ethoxytetrahydrofuryl-(3) N-[2-methyl-4-aminopyrimidyl-(5)]-methyl-dithiocarbamate (IX). This kind of condensation was not witnessed when cyclic isomer of (II), 2-methyl-2-ethoxy-3-chlorotetrahydrofuran (X), was used instead of (II).