Studies of thiazolopyridines, part 6:: Synthesis and antimicrobial evaluation of some novel thiazolo[3,2-a] pyridine and thiazolo[2′,3′:6,1]-pyrido[2,3-d]pyrimidine derivatives

Condensation of thiazolinone 1 with aromatic aldehydes yielded the corresponding methylidene derivatives 2a-f Cyclization of compounds 2a-f with arylidene-malononitrile 3 (1:1 molar ratio) in ethanol in the presence of,piperidine furnished the novel thiazolo[3,2-a]pyridines 5a-v, via Michael adduct 4. Compounds 5p,r were cyclized with malononitrile in the presence of piperidine to yield thiazolo[3,2-a][1,8]naphthryidines 7a,b. Thiazolo-[2',3':1,6]pyrido[2,3-d]pyrimidine 9a-c were obtained by cyclization of compounds 5c,p,r with formic acid. The structure of the synthesized compounds was established by analytical and spectral data. Also, some of the synthesized compounds were screened for antimicrobial activity in vitro.