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 6H‐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.

The use of malonates such as diethyl malonates 9, (chlorocarbonyl)ketenes 15 and bis(2,4,6-trichlorophenyl) malonates 18 as reagents for cyclocondensation with 1,3-dinucleophiles to give six-membered heterocycles is described. Further attempts to use malonates such as bis(trimethylsilyl) malonates 19 and bis(carbamimidoyl) malonates 29 as new cyclocondensation agents are described .

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4‐Chloro‐3‐nitro‐2‐quinolones 3 obtained from the 4‐hydroxy quinolones 1 by nitration and chlorination, reacted with sodium azide to the 4‐azido derivatives 4 which cyclized on thermolysis to yield the furoxanes 5. Nucleophilic substitution reactions of 3 led to the 4‐amino‐, 4‐fluoro‐ and 4‐alkoxy‐3‐nitroquinolones 7, 8 and 9, respectively. With thiols either 4‐thio‐3‐nitro‐ 10 or 3,4‐dithioquinolones 11 were obtained depending on the basic catalyst.

Thermolysis of the 3-acetyl-4-azido-2-quinolone 6, which was obtained from the corresponding 4-tosyloxy derivative 5, afforded the ring closed isoxazoloquinolone ? in good yield.The cyclization of ortho-substituted azido arenes and heteroarenes by thermo-or photolysis is a well-known reaction'). These reactions have been applied by us to some heterocyclic systems (e.g. coumarins, quinolines, pyrimidines and pyridazines) bearing aryl or benzyl groups in ortho position3). Another type of ortho substituents which should cyclize easily with azido groups are carbonyl groups as in acyl or cyano groups4).We studied the thermolysis of 4-azido-2-quinolones, which bear an acetyl group in the 3-position. According to the findings of Suschitzky and co-workers 5, also the influence of the ortho substituent on the thermolysis temperature was of interest.3-Acetyl-4-hydroxy-l-methyl-2(1H)-quinolone (3) was prepared by an improved two-step procedure developed for pyridones6) from N-methylaniline and diethyl malonate. By the addition of diphenyl ether the yield of the pyrone 2 increased from 55%7) to 66%. The degradation of 2 to the 3-acetylquinolone 3 was performed in 1,2ethanediol/aqueous sodium hydroxide during 1 h (instead of 24 h in aqueous sodium hydroxide solution7)) to yield the highly pure acetyl compound 3.The usually applied method for preparing 4-azidoquinolones proceeds via the corresponding 4-chloroquinoloness~. However, all attempts to convert the 4-hydroxyquinolone 3 into the 4-chloroquinolone 4 failed. Either no reaction took place or, under drastic conditions, the 3-acetyl group was cleaved to yield the 3-unsubstituted 4-hydroxy-1-methyl-2-quinolone.Another method to introduce the azido group is the conversion of the hydroxy group into the reactive tosyloxy group**). Direct tosylation of 3-acetyl-4-hydroxyquinolone 3 failed, but reaction of the sodium salt of 3 resulted in the formation of the desired 3acetyl-4-tosyloxyquinolone 5, a very reactive compound, which can