Thiazinium hydroxides

Bielectrophiles have found appreciable applications in the synthesis of ring-fused systems, especially those involving [5,6] fused systems. The following serve to illustrate these applications. Reaction of pyrazole with (chlorocarbonyl)phenyl ketene (214) (Type 1, Scheme 6) readily formed the zwitterionic pyrazolo[l,2-a]pyrazole derivative (215) (80JA3971). With l-methylimidazole-2-thione (216), anhydro-2-hydroxy-8-methyl-4-oxo-3-phenyl-4//-imidazo[2,l-6][l,3]thiazinium hydroxide (217) was obtained (80JOC2474). 

Dipolar cycloaddition of betaines 492 gave cycloadducts 493, which produced tricyclic compounds 494 on further thermolysis (Scheme 48) <1995H(41)1631>. Heating 9,9-disubstituted yr/ra-(4-hydroxy-2-oxo-2//-pyrido-[2. -//][ 1.3]thiazinium) hydroxides 495 afforded tricyclic compounds 497 as diastereomeric mixtures (Scheme 49) <1995S973>. In the case of the lower homolog (n = 0), a cycloadduct 496 could be also isolated at lower temperature. 

The structures of anhydro 9,9-dimethyl-4-hydroxy-2-oxo-6,7,8,9-tetrahy-dro-2H-pyrido[2,l- >] [1,3]thiazinium hydroxide (95JOC3795,95T6651) and llh-isopropyl-2-methoxy-3,4-diphenyl-2,6,7,llh-tetrahydro-[l,3]thiazino-[2,3-a]isoquinoline [79AX(B)1285] were determined by means of X-ray diffraction analysis. 

Dipolar cycloaddition of anhydro pyrido[2,l-b][l,3]thiazinium hydroxides (128) with aryl isocyanates and dimethyl acetylenedicarboxylate gave pyrido[l,2]pyrimidines (129) and quinolizine-l,2-dicarboxylates (130), respectively (76CB3668). 1,4-Dipolar cycloaddition of pyrido[2,l-h][l,3]thi-azinium betaine (131, R = Me) with 1-diethylamino-l-propyne afforded cycloadduct 132, from which quinolizin-4-one 133 formed by a rapid cheletropic extrusion of carbonyl sulfide (93TL5405 95T6651). 1,4-Dipolar cycloaddition of anhydro 4-hydroxyl-2-oxo-6,7,8,9-tetrahydro-2//-pyrido-[2,l-b][l,3]thiazinium hydroxides (131) and 4-phenyl-l,2,4-triazoline-3,5-dione yielded 135 via 134 [94H(39)219 95H(41)1631] and 136 (95T6651). 

The UV and CD curves of optically active (S)-9-hydroxy-6-methyl-3,4-dihydro-2//-pyrido[2,1 -6] [1,3]thiazinium-4-carboxylate were measured in 1 N hydrochloric acid and in 1 N sodium hydroxide solutions (73ACS1059). The CD spectrum in acid solution exhibits positive bands at 212 and 233 nm and negative bands at 257 and 345 nm, and UV maxima were found at 211, 239, and 342 nm. The two latter bands are associated with the aromatic chromophore. In alkaline solution a bathochromic shift occurred, and the... 

NMR and optical rotation measurement demonstrated that deuterium incorporation on the chiral C-4 in 9-hydroxy-6-methyl-3,4-dihydro-2H-pyrido[2,l-b][l,3]thiazinium-4-carboxylate in 0.4 N sodium hydroxide at 40°C occurred without racemization (73ACS1059). 

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