Preparation of N-Alkyl-N′-4-Pyridylthioureas via Isolable 4-Pyridylisothiocyanate or via Aerial Oxidation of 4-Pyridyldithiocarbamic Acid

Abstract

N-Alkyl-N′-4-pyridylthioureas (4) which are intermediates for antihypertensive cyanoguanidines^1,2 have been prepared from S-methyl 4-pyridyldithiocarbamate (5)³ and the requisite amines ^1,2 (Method A, Scheme 1). (5) was obtained by S-methylation of 4-aminopyridinium 4-pyridyldithiocarbamate (1)(Scheme 1) which was the sole product isolable from the reaction of 4-aminopyridine with carbon disulfide in different media, also in the presence of e.g. triethylamine^3,4. Since this method required 2 equivalents of methyl iodide and resulted in the loss of one half of the 4-aminopyridine due to quaternization, a better method was needed.