Pyrido thiazolo

Reaction between 2-chIoronicotinic acid (130) and 2-amino-4-phenyl-thiazole furnishes 3-phenyl-5-H-pyrido[2,3,-d]thiazolo[3.2-fl]pyximidin-5-one (131) (Scheme 86) (293). This reaction was extended to other pyridinyl compounds (294). 

Amongst the more unusual reactions, 2,3-thiazolo fused pyrido[3,2-d]pyrimidines have been prepared from 3-aminopicolinic acid and 2-bromothiazoles, whilst a similar derivative resulted with allyl isothiocyanate (221 222) <72IJC602). Similar products are also produced in [3 + 3] reactions of 2-aminothiazoles (Section 2.15.5.7.1). 

Alkylation of 694 with phenacyl bromides, followed by cyclization with acetic anhydride gave (87H2183) thiazolo[2,3-c]pyrido[2,l-/][ 1,2,4]-triazine 695. 

The reaction of 2-aminothiazole and isopropylidene bis(methylthio)-methylenemalonate (459, R2 = R3 = SMe) or 1-methylthioalkylidenema-lonates (459, R2 = Me, Et, Ph R3 = SMe) in boiling ethanol for 2.5 hr or in dimethylformamide at 120-130°C for 4-5 hr, gave 2-substituted 5-oxo-5//-thiazolo[3,2-a]pyrimidine-6-carboxylates (462) in good yields (89S-317). Similarly, in boiling ethanol, 2-substituted 4-oxo-4//-pyrido[l,2-a]-pyrimidine-3-carboxylic acids (463) were obtained in 80-85% yields. When anilines were reacted with isopropylidene bis(methylthio)methy-lenemalonate (459, R2 = R3 = MeS), (methylthio)(arylamino)methylene-malonates (464) were obtained 61-88% yields. 

Methylenedioxypyrimido[2,l-b]benzothiazolecarboxylate (1148) and pyrido[3, 2 4,5]thiazolo[3,2-a]pyrimidinecarboxylate (1149) were prepared in the reaction of 2-amino-5,6-methylenedioxobenzothiazole and 2-amino-6-methoxypyrido[2,3-c/]thiazole with EMME in Dowtherm A at 220°C (73JHC769). 

Treatment of 3,6-dihydroxy-3,4-dihydro-2//-pyrido[2,l-h][l,3] thiazinium salt (86) with orthophosphoric acid at 140°C for 34 h or with cone, sulfuric acid at ambient temperature for 5 h afforded 1 1 and 3 1 mixtures of pyrido[2,l-6][l,3]thiazine (87) and thiazolo[3,2-a]pyridine (88), respectively (70ACS2949). Under basic conditions, only extensive destruction of 86 was observed. When 3-hydroxy-2,3,4,6-tetrahydro[l,3]thiazino[2,3-a]isoquinolin-6-one was left to stand in cone, sulfuric acid at room temperature overnight, 4,6-dihydro[l,3]thiazino[2,3-a]isoquinolin-6-one was obtained in 61% yield (72ACS1620). 9-Oxido-3,4-dihydro-2H-pyrido[2,l-h] [l,3]thiazinium betaine did not undergo cycloaddition even under extreme conditions [81JCR(S)208],... 

Thiazole-containing pyridoacridines are a group of fused ring alkaloids having a pyrido[4,3,2-w, ]thiazolo[3,2-6]acridinium skeleton related to shermilamines, varamines and diplamine, which were discussed in the sulfide section [37]. The pyridoacridines have a characteristic UV absorption pattern [A.max(MeOH) 245, 307, and 361 nm], which is highly sensitive to the pH of the medium. 

Disubstituted 2-thioxo-pyrido[2,3-d]pyrimidinones condensed with aldehydes in the presence of chloroacetic acid to yield thiazolo[2,3-a]pyrido[2,3-. One-pot alkoxylation at the 7-position of 6-arylpyrazino[2,3-c][l,2,6]thiadiazine 2,2-dioxides with NBS or NCS in the appropriate alcohol has been studied <02EJ02109>. 

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