1,3-Thiazinium perchlorates

Rearrangement reactions involving 1,3-thiazines are often very facile. For example, reaction of 2-imino-4-phenyl-2/7-1,3-thiazinium perchlorate 957 with NaOH at room temperature gave 4-phenylpyrimidine-2(l//)-thione 958 <2004CHE1595>, while treatment of 6-amino-2,3-dihydro-l,3-thiazin-4(l// )-ones 959 with KOH readily gave the potassium salt of the dihydropyrimidinone 960 <2005HAC426>. 

Oxazinium perchlorates (267) are obtained by reactions of 1,3-diketones and benzonitrile in the presence of perchloric acid and acetic anhydride (88ZOR1561, 88ZOR2232, 91ZOR1986). 1,3-Thiazinium perchlorates are synthesized by treating oxazinium salts with hydrogen sulfide in absolute acetonitrile and then with perchloric acid (72S333). 

Methylthio-4,6-diphenyl-1,3-thiazinium perchlorate (101) reacts with primary amines and active methylene compounds at C-2 to give the 2-imino (102) and the methylene derivatives (103), respectively. However, hydrazine and hydroxylamine give 3,5-phenylpyrazole (104) and 3,5-diphenyl-isoxazole (105), respectively, and it is possible that here the reactions proceed through initial nucleophilic attack at C-4 as indicated in Scheme 14 <87NKK780>. 

The only known fully unsaturated 1,3-thiazepines are ethyl 2,4,7-triaryl-l,3-thiazepine-6-car-boxylates 2, which are formed in moderate yield by the action of ethyl diazoacetate on 2,4,6-triaryl-l,3-thiazinium perchlorates 1 in a reaction analogous to that of oxazinium salts the preparative procedure is analogous to that given for ethyl 2,4,7-triaryl-l,3-oxazepine-6-car-boxylates (see Section 4.1.1.2.1.1.).13... 

Chlorovinyl ketones (253) and the thioamide (254) in the presence of perchloric acid give intermediate thioimidium salts (255), which cyclize to yield 1,3-thiazinium salts (256) (82T937). 

Diamino-1,3-thiazinium salts (179) are obtained in a similar way from 2-acyl-1-chloro-enamines (180) and thioureas in the presence of either perchloric or tetrafluoroboric acid (X = CIO4 or BF4), but if the enamines (180) are reacted with thiobenzamide the products are 4-amino-1,3-oxazinium salts (181) (Scheme 33) <87M1383>. 

Disubstituted l,3-thiazin-4-ones (279) may be synthesized by successive treatment of -ketoimides (280) with perchloric acid and hydrogen sulfide, followed by the basification of the product 4-hydroxy-1,3-thiazinium salts (281) with sodium carbonate (Scheme 54) <83CPB1929>. 

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