4- Hydroxy-3,4-dihydro-2//- thiazino

The same substrate (25) aud ethyl 2-chloroacetoacetate gave an analogous product, ethyl 3-hydroxy-3-methyl-3,4-dihydro-2//-1,4-thiazino[2,3-h]qui-noxahne-2-carboxylate (27) (KOH, EtOH, 20°C, 3 h 58%), which underwent dehydration to ethyl 3-methyl-2H-1,4-thiazino[2,3-h]quinoxaline-2-carboxy-late (28) (HCl gas, EtOH, 20°C, 15 h 60% analogs likewise). ... 

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],... 

Cyclization of 1-isoquinolyl derivatives (201) in a cold solution of perchloric acid or in cone, sulfuric acid at room temperature afforded 4-hydroxy-3,4-dihydro-2//-[l,3]thiazino[2,3-a]isoquinolinium perchlorates (202) and 2H-[l,3]thiazino[2,3-a]isoquinolinium salts (203), respectively (74IJC1242). Heating l-[(3-phenyl-3-hydroxypropyl)thio]isoquinoline in PPA yielded the l-phenyl-3,4-dihydro-2//-[l,3]thiazino[2,3-a]isoquin-olinium salt (74IJC1242). 6,7-Dihydro derivatives of 2//-[l,3]thiazino-[2,3-a]isoquinolinium perchlorate (203, R = Me) and 4-methyl-2,3,4,6,7, llh-hexahydro-[l,3]thiazino[2,3-a]isoquinoline were obtained by cyclization of the 3,4-dihydro derivative of 201 (R = Me) and 4-[(l,2,3,4-tetrahydroisoquinolin-l-yl)thio]-2-butanol, respectively, in cone, sulfuric acid or in PPA [81IJC(B)372],... 

C7H9N3O2S, 7,8-Dihydro-8-hydroxy-2-methy1-3H,6H-(1,3)thiazino[3,2-b] (1,2,4)triazine-3-one, 40B, 340... 

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