1,3-Thiazine ring, dihydro— from

A sulfone group incorporated within a l,l-dioxo-l,4-thiazine ring is also present in 6-(p-hydroxyphenyl)-2i/-3,4-dihydro-l,l-dioxo-l,4-thiazine (286), a compound obtained from the sponge Anchinoe tenacior [211], and in euthyroideones A-C (287-289), which are brominated quinone methides isolated from the New Zealand bryozoan Euthyroides episcopalis (order Cheilostomatida, suborder Ascophotina, family Euthyroididae) [212]. The spectral data of euthyroideone A (287), secured by X-ray analysis, was used for the structural determination of euthyroideones B (288) and C (289). Compound 288 showed a weak cytotoxic activity towards the BSC-1 cell line. 

Dihydrobenzo-TAs 164 may be obtained from compounds containing a 1,3-thiazine ring, for example, by oxidation of 2,3-dihydro-l,3-benzothiazine-4-thiones (55BSF1518) (Scheme 56). The reduction of 1,3-benzo-TA, affording 2,3-dihydro derivatives, is described in Section III,C,6. 

Hydroxy-2,3-dihydro-l,4-thiazine ring from 2,3-dihydro-l,4-thiazine 1-oxide ring... 

Heterocyclics from carbohydrates Ring closure with sulfonic acid esters Dihydro-1,4-thiazine ring... 

Similar ring systems were prepared <97JHC1693> by Coppo and Fawzi from the reaction of substituted ethyl 5-[methyl(methylsulfonyl)amino]-l 7/-pyrazole-4-carboxylates 119 with sodium hydride. This gave the 7-substitued 1,7-dihydro-l-methylpyrazolo[3,4-c][l, 2]thiazin-4(37/)-one 2,2-dioxides 120 in fair to good yield (Scheme 30). They also extended this synthesis by treating methyl 2-[methyl(methylsulfonyl)amino]-6-(trifluoromethyl)-3-pyridinecarboxylate 121 with sodium hydride in dimethylformamide to yield l-methyl-7-(trifhioromethyl)-l//-pyrido[2,3-c][l,2]thiazin-4(3//)-one 2,2-dioxide 122 in 79% yield (Scheme 31) <98JHC499>. 

Routes to dihydro-1,4-thiazines are more diverse (B-78MI22701). For example, ring expansion of the thiazolidine (273) by heating with elemental sulfur and n-butylamine affords a 3 1 mixture of the isomers (276) and (277) and it appears likely that these products are derived from their tautomers (274) and (275) respectively which are the initial reaction products (Scheme 118) (70LA(739)32). Thiazolidines also accompany dihydrothiazines as products when aldehydes or ketones are reacted with aziridines in the presence of sulfur and DMF or potassium carbonate and it seems certain that a similar mechanistic sequence is involved (79M425). 

Dihydro-4H-l,4-thiazines from penicillin ring skeleton... 

Pyrrole from a/iAj dir -4-hydroxyimidazolium hydroxide ring and acetylene derivs. O 3,4-Dihydro-2 f-pyrrolo 2,l- l,3 thiazines... 

Dihydro-1,2-thiazine 1-oxide ring from ethylene derivatives Ring closure with thionylimines... 

Dihydro-1,3-thiazine-6-thione ring from 0x0 compds. 

Thermal decomposition of ( >-azidophenylthio)uracil (299) furnishes a 2 1 mixture of the dihydro-5-thia- (300) and dihydro-10-thia-isoalloxazines (301). The formation of the former product is analogous to the preparation of pheno-thiazines from o-azidodiphenyl sulphides, and presumably involves rearrangement via a Spiro-intermediate. However, the direct insertion of the nitrene intermediate derived from azide (299) into the uracil ring to give the 1,4-benzothiazine system (301) is unique. More surprising is the production of the unrearranged 10-thiaisoalloxazine (301) (70%) as the only product from the photolysis of (299) in methanol solution. 

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