Thiazolidines 1,4-thiazines, 5,6-dihydro

Thiazolidine, 2,5-Dihydro- 1,3-thiazole, Tetrahydro-l,3-thiazine und 5,6-Dihydro- 1,3-thiazine werden durch Lithiumalanat6,7 und meist auch durch Natriumboranat7 zu den (w-Mercapto-aminen aufgespalten. 1,3-Thiazolidine lassen sich mit einem Lithi-umalanat-OberschuB ahnlich den 4,5-Dihydro-1,3-oxathiolanen zu Athylaminen wei-terreduzieren7,8 ... 

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). 

Although the precise pathway involved in the aforementioned synthesis has not been established, it is clear that 3,4-dihydro-2//-l, 4-thiazines are formed in preference to thiazolidines, which, in turn, are preferred to 5,6-dihydro-2if-1,4-thiazines. The dihydrothiazines are probably produced from a-mercaptoketones, formed by the action of elemental sulfur upon the ketones, and aziridine. It seems likely that the thiazolidines arise from the reactions of the ketones with )3-mercaptoethyIamine, produced from aziridine and hydrogen sulfide a competing reaction of the a-mercaptoketone with sulfur is probably responsible for the generation of hydrogen sulfide. 

Attempts to utilize aldehydes in place of ketones in the foregoing reactions have met with limited success. Thus propanal, in the presence of N,N-dimethylformamide or potassium carbonate, reacted with sulfur and aziridine to give a 1.3 1 mixture of 3,4-dihydro-6-methyl-2H-l,4-thiazine and 2-ethylthiazolidine in 23% yield. Although somewhat better yields were achieved by using butanal and pentanal, the thiazolidines were then the predominant products. 

Treatment of 1,3-thiazolidines (116) with chlorine affords dihydro-1,4-thiazines (117) through the ring opening of a unisolable chlorosulfonium salt (Scheme 26) <93JHC1105>. 

Optically active thiazolidine -oxides (259) undergo the silicon Pummerer reaction with t-butyldimethylsilyl trifluoromethanesulfonate or iodotrimethylsilane <87TL5903>. When the former is used as silylating agent, thiazolidines (260) and 4-thiazolines (261) are obtained. With iodotrimethylsilane, the iodothiazolidines (262) and the dihydro-1,4-thiazine (263) are obtained (Scheme 65). 

Dihydro-l,3-thiazin-4-ones s. 23, 592 thiazolidine derivs. cf. H. Nagase, Chem. Pharm. Bull. 21, 270, 279 (1973)... 

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