Sulfur-containing Pyridine Derivatives. LIV

Smiles Rearrangement in Pyridine Derivatives and Synthesis of Benzopyrido- and Dipyridothiazine Derivatives. (2)

Abstract

In order to compare with 2-arylthio-3-amino-6-chloropyridine derivatives prepared earlier*, derivatives of 2-arylthio-3-amino-6-methoxy (or ethoxy) pyridine, and 3-amino-4-arylthiopyridine with the chlorine in the earlier compounds substituted with methoxyl or ethoxyl groups, were submitted to the Smiles rearrangement. It was found that free amine resisted rearrangement and that a nucleophilic substitution with CH₃O^-, formed from methanolic potassium hydroxide used as the rearrangement catalyst, occurred more preferably than the rearrangement. This result indicates the great effect of chlorine in 6-positions in the earlier chlorine derivatives, which underwent facile rearrangement even with free amino group. However, it was found that the acetyl derivatives easily underwent rearrangement even in the cold, as in the case of chlorine derivatives. With reference to 2-aminoarylthiobenzene derivatives, which hardly undergo rearrangement in the cold, the present results indicate that pyridine derivatives possessing amino in 3-position and mercapto group in 2- or 4-position are generally liable to this arrangement. Two kinds of benzopyridothiazine were prepared by the use of this Smiles rearrangement.