Synthesis and reactions of “biginelli‐compounds”. Part I

Various reactions of 2‐oxo(or thioxo)‐1,2,3,4‐tetrahydropyrimidine‐5‐carboxylic acid derivatives (Biginelli‐compounds) were investigated. The site of methylation and acylation on 6‐methyl‐4‐phenyl‐2‐thioxo‐1,2,3,4‐tetrahydropyrimidine‐5‐carboxylic acid ethyl ester 1a and its 2‐oxo derivative 9a was studied. The synthesis of pyrimido[2,3‐ b ]thiazines and thiazolo[3,2‐ a ]pyrimidines was accomplished by condensation of 1a with 1,3‐and 1,2‐dielectrophiles. A Dimroth‐like rearrangement yielding 6 H ‐1,3‐thiazines can be observed when 1a was treated with dimethylformamide and phosphorus oxychloride. The formation of indeno[1,2‐ d ]pyrimidines can be achieved by intramolecular Friedl‐Crafts acylation of 9a and 13 , respectively. Finally a route for the preparation of 4,6‐disubstituted‐pyrimidine‐5‐carbonitriles is presented, starting with Biginelli‐compound 25 .