Über die Reaktionen von Guanidin bzw. Thioharnstoff mit α,β,γ,δ-ungesättigten Ketonen

Guanidine and phenylguanidine react with phenylhexadienone1b and 1,5-diaryl-2,4-pentadien-1-ones1c–k respectively (via unstable dihydropyrimidines of type2 as intermediates) to 4-methyl- and 4-aryl-6-styryl-2-pyrimidinamines3b–j and N²-phenyl-2-pyrimidinamines7c, k. Efforts to stabilize the intermediates2 by introduction of electron-withdrawing substituents (compare^2,3) were not successful. Similarly, thiourea reacts with diphenylpentadienone1c to afford (via8c) 4-phenyl-6-phenethylpyrimidinethione9c. Action of guanidine on 1,3,5-triphenylpentadienone101 and on the 5-(3-chlorophenyl) analogue10m under decomposition of the ketones yields 4,6-diphenyl-and 4-(3-chlorophenyl)-6-phenyl-2-pyrimidineamine (121 andm), respectively. The formation of12m proves that acetophenone splits off from101,m during the reactions. However, heating of thiourea with10m in sodium butylate/butanol gives the expected 4,6-diphenyl-4-styryldihydropyrimidinethione13m. The reaction of thiourea with triphenylpentadienone101 is taking an atypical course: Addition of thiourea to the δ- and β-carbon atom of101 affords 2-(4,6-diphenyl-2-thioxohexahydro-4-pyrimidinyl)acetophenone (141); the conformation of the latter was deduced from¹H-NMR data.