Studies on thiazolopyridines. Part 5: Synthesis of hitherto unknown thiazolinone and thiazolo[3,2-a]pyridine derivatives having in their structure the morpholin-4-yl moiety

Article abstract of DOI:10.1080/10426500490468092

Condensation of thiazolinone 1 with, benzaldehydes 2a,b in ethanolic piperidine afforded the methylidene derivatives 3a,b. Cyclocondensation of compound 3b with malononitrile furnished the novel thiazolo[3,2-a]-pyridine 5. Also, compound 3b was condensed with dimethylformamide-dimethylacetal (DMF-DMA) and triethylorthoformate to yield N,N-dimethylamino 6 and ethoxymethylene 7 derivatives respectively. The novel thiazolo[3,2-a]pyridines 10a,b were obtained by cyclocondensation of compounds 3a,b with benzylidenemalononitriles 8a,b. Similarly, cyclocondensation of compound 3b with benzylidenemalononitrile 11 afforded the thiazolopyridines 12a-c. Ternary condensation of compound (12), 4-morpholinobenzaldehyde 2b and malononitrile (1:1:1 molar ratio) produced, the thiazolopyridines 14a-c. When compound 10b was subjected to react with malononitrile in dioxane/piperidine under reflux the novel condensed heterocyclic system 18 was obtained. Treatment of ortho-aminocarbonitrile 10b with formic acid, aromatic aldehyde and triethylorthoformate furnished the thiazolo[2′,3′:1,6]pyrido[2,3-d] pyrimidine 20, azomethine 21a,b and ethoxymethylene 22 derivatives respectively. The structure of the synthesized compounds was established by analytical and spectral data.