Diethyl 2‐amino‐6‐methylpyridine‐3,4‐dicarboxylate (I) is coupled with the isocyanates (II).

The pyridoisothiazoline (Ia) reacts with sodium ethoxide to give the nicotinic acid (II).

220ChemInform Abstract The N-(aminoethyl)thioureas (III), prepared from N,N-diethyl-1,2-diaminoethane (I) and the thiocyanates (II), are coupled with the pyridinedicarboxylate (IV) to produce the pyridopyrimidines (V). The N-(hydroxyalkyl)thioureas (IX), however, react with (IV) to yield the pyridothiazines (X). The derivative (IXc) shows a regioselectivity which is contrary to that of (IXa) and (IXb) in this ring closure reaction. Several experiments of basic and acidic hydrolysis are performed with (V) and (X) resulting in ring cleavage and/or saponification. Acidic treatment of (Xc) gives the heterocycle (XIV) containing a nine-membered ring. (XIV) undergoes degradation under various conditions, forming the compounds (XV) -(XVII). (IR-, 1H-NMR-data).

The isothiazole (I) is oxidized to produce mixtures of the sulfone (II) and the carbonamidosulfonic acid (III).

Diethyl 2‐amino‐6‐methylpyridine‐3,4‐dicarboxylate (I) is cyclized with the isothiocyanates (II) to yield the thioxopyrido(2,3‐d)pyrimidinecarboxylates (III).