Thiazolo salts, dihydro

Thiazolo[2,3-6]oxazolium salts, 2,3-dihydro-synthesis, 6, 992 Thiazolo[2,3-6]pteridines structure, 3, 284 Thiazolo[3,2-a]pteridines structure, 3, 284 Thiazolopurines, 5, 566... 

Thiazolo[3,2-a]pyridinium salts, 3-carboxy-2,3-dihydro-8-hydroxy-8-methyl-desulfbrization, 6, 687-688 Thiazolo[3,2-a]pyridinium salts, 6(8)-nitro-2,3-dihydro-... 

Several groups have reported reactions giving thiazoloquinazoline compounds, probably the most interesting of which is the cyclization-ring expansion of the aziridine thiourea derivative 225 to the dihydro-thiazolo[2,3-6]quinazoline 226 in hydrochloric acid of Howard and Klein.395 Other preparations of this ring system involve the treatment of l-(2-carbethoxyphenyl)-2-thioureas with a-chloro 396-398 or a-bromo396,397 ketones or with vicinal dibromides.398 Tetrahydro salt... 

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],... 

Dihydro-2iT-thiazolo[2,3-c][l,2,4]triazine-3,4-dione rearranges in dilute base to give an unstable acid which decarboxylates on acidification of the sodium salt to give 5,6-dihydrothiazolo[2,3-c]-s-triazole (equation 68) (81CB1200). Kinetic evidence has been put forward in favor of covalently hydrated intermediates in the acid-catalyzed rearrangement of triazolo[4,3-a]pyrazines to 1H-imidazo[2,1 -c]-s-triazoles. The intermediate triazole has been isolated and characterized (equation 69) (72JCS(P2)4). 

Similar 1,3-dipolar additions have been observed recently in the reaction of carbon disulfide with N-benzyl isoquinolinium salts (CXLVIII) in basic medium (228). The dipolarophile carbon disulfide also adds readily to these azomethinylides (CXLIXa, b) and, via the 3-(R)-2J-dihydro-l i H-thiazolo[2,3-aJisoquinoline-2-thiones (CL), the meso-ionic compound (CLI) is formed by a redox-reaction. 

Three methods were reported to obtain the title compounds. The first was based on a reaction sequence starting from 5,6-diamino-4-thiouracil-sodium salt, alkylation with 1,2-dibromoethane to 7,8-diamino-2,3-dihydro-5//-thiazolo-[3,2-c]pyrimidine (135) and fusion with urea or thiourea under formation of a third ring to the respective 7,8-dihydrothiazolo[2,3-/]purine-2,5(l//,3//)-dione (136) and 2,3,7,8-tetrahydro-2-thioxothiazolo[2,3- ]purin-5(l//)-one (137) (92FES1315) (Scheme 37). 

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