1.3- Thiazinium salts

Reduction of 1,3-thiazinium salts in acetonitrile yields 6,6 -di-l,3-thiazinyls formed by dimerization of a short-lived radical oxidation at a platinum anode regenerates the thiazinium salt, whereas oxidation with chloranil yields 6,6 -di-1,3-thiazinylidenes.2 71... 

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). 

W-1,4-Thiazines are formed when the sulfides (314) are reacted with ammonia (Scheme 47) (67JMC591). The 3,4-dihydrothiazine-3-thione (315) is converted by methyl iodide into the thiazinium salt (316), deprotonation of which yields a 4//-thiazine (317) (69JHC247). 1,4-Thiazine 1,1-dioxides are formed by the cyclodehydration of diacyl sulfones and ammonia (Scheme 48) (720S(52)135). 

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],... 

Simple 6H- 1,3-oxazines and -thiazines are commonly encountered as intermediates in the reactions of oxazinium and thiazinium salts with nucleophiles (see Section 2.27.2.2.3). Additionally there is a considerable interest in 6//-1,3-thiazines as intermediates in the synthesis of cephem antibiotics (see Section 2.27.3.24) and many approaches have been... 

The 3,4-dihydrothiazine-3-thione (236) is converted into the 2/f-thiazine (237) by direct. S-ethylation with triethyloxonium tetrafluoroborate. With methyl iodide S,JV-dimethylation occurs to give the thiazinium salt (238), deprotonation of which yields a 4H-thiazine (239) (69JHC247). 

The 3,4-dihydrothiazine-3-thione 465 is converted by methyl iodide into the thiazinium salt 466, deprotonation of which yields a 4//-thiazine 467 (Scheme 217) <1969JHC247>. 

Reduction of 1,3-thiazinium salts in acetonitrile yield 6,6 -bi-l,3-thiazinyls the 6,6 -bi-l,3-thiazinyls are oxidized to thiazinium salts at a platinum electrode, whereas dehydrogenation by chloranil affords 6,6 -bi-l,3-thiazinylidene [293]. 

A simple and efficient route to alkylmercaptomethyleneiminium salts (110 equation 67) is the action of alkyl thiochloroformates on thioamides. - - 3-Chlorovinyl ketones react with thioamides to form iminium compounds (111 equation 68), - - which can serve as precursors for 1,3-thiazinium salts. Bromine forms labile S-bromoiminium salts (112) with thioamides, - which react with en-amines to give S-vinyl-substituted salts (113 equation 69). ... 

H-1,4-Thiazines are weak bases (Section 11,D,5), and the parent compound is reported to form salts with picric acid, chloroplatinic acid, and hydrogen chloride. Alkylation, to give the thiazinium iodide 25, occurred when the thiazine 15 was treated with methyl iodide the derivative 25 is the only known example of a 4//-l,4-thiazinium salt. 

The C =N bond of 2/f-l,4-thiazinium salts is expected to be particularly susceptible to attack by nucleophilic reagents. Two examples involving the compound 23 are known thus, with diazomethane and triethyl phosphite, the thiazinium chloride 23 afforded the derivatives 28a and 28b, respectively. ... 

Thiazinium salts (78) undergo reductive dimerization on cathodic reduction to afford 6,6 -bithiazinyls (79) (Scheme 10) <81JPC33>. However, 5-acyl-2-phenyl-6//-l,3-thiazines (80) undergo electrochemical reduction under controlled conditions and at 2°C to yield 3,6-dihydro-2//-l,3-thiazines (81) and dihydrodimers (82) coupled through C-2. Further reduction leads to tetrahydro-... 

Thio-l,3-thiazinium salts (106) when reacted with thiols afford dithioacetals (107), which on thermolysis yield 6,6 -bi(l,3-thiazinylidenes) ((108) and (109)). The same final products are formed directly from the thiazinium salts if triethylamine is added in the first step, or if the thiones (110) are heated with triethyl phosphite in toluene (Scheme 15) <86S916>. 

Chloro-5,6-dihydro-4//-l,3-thiazinium salts (134) are strongly electrophilic and react with enamines and other nucleophiles by displacement of the chlorine atom as the chloride ion and the formation of 2-substituted derivatives. With the pyrrole (135) and indole this leads to the 2-(pyrrol-... 

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