Syntheses of hitherto unknown thiazole, ylidene and pyridinethione, derivatives having a piperidin-1-yl moiety and their use as antimicrobial agents

The novel hydrazone derivatives 2a-c were prepared by treatment of aldehydes I a,b with some hydrazines. Thiocarbamoyl functional group in compound 2a was subjected to cyclization reactions with some alpha-halocarbonyl reagents and furnished the novel thiazoles 4-6, 8 and 9. Enaminonitrile 10 and pyridinone 13 derivatives were synthesized by interaction of active methylene compound 2b with NN-dimethylformamide-dimethylacetal and ketene dithioacetal 11, respectively. Aliphatic, aromatic and heteroaromatic active methylene compounds were condensed with aldehydes 1a,b to afford the new ylidenes 15a-d, 19a,b, 20 and 21. Substituted pyridinethiones 22 and 23 were prepared in high yields by cyclocondensation of 15c with malononitrile and ethyl cyanoacetate, respectively. Indeno[1,2-b]pyridines 26a,b were obtained by the reaction of ylidenes 19a,b with cyanothioacetamide in ethanol and in the presence of sodium ethoxide under reflux. The structures of the synthesized compounds were established from their analytical and spectral data. The prepared compounds were also screened for their antimicrobial activity.