1.3- Dithiolylium salts

All neutral azoles possess positively charged azolium counterparts. In addition, as di cussed in Chapter 4.01, certain olylium species exist which have no neutral counterpart for example dithiolylium salts. 

Most azolium ions are sufficiently reactive to be attacked by amines. Sometimes the initial adducts are stable ammonia and primary and secondary amines add to 1,3-dithiolylium salts at the 2-position to give compounds of the types NT3, RNT2 and R2NT, respectively, where T = the l,3-thiol-2-yl group (80AHC(27)l5l). 

Data on reactions of sulfur nucleophiles with azoles are sparse. Oxazoles are transformed in low yield into the corresponding thiazoles over alumina with HiS at 350 °C (74AHC( 17)99). Sulfur nucleophiles such as SH or RS add to 1,3-dithiolylium salts at the 2-position... 

Cationic rings are readily reduced by complex hydrides under relatively mild conditions. Thus isoxazolium salts with sodium borohydride give the 2,5-dihydro derivatives (217) in ethanol, but yield the 2,3-dihydro compound (218) in MeCN/H20 (74CPB70). Pyrazolyl anions are reduced by borohydride to pyrazolines and pyrazolidines. Thiazolyl ions are reduced to 1,2-dihydrothiazoles by lithium aluminum hydride and to tetrahydrothiazoles by sodium borohydride. The tetrahydro compound is probably formed via (219), which results from proton addition to the dihydro derivative (220) containing an enamine function. 1,3-Dithiolylium salts easily add hydride ion from sodium borohydride (Scheme 20) (80AHC(27)151). 

Base-catalyzed hydrogen exchange occurs at the 3- and 5-positions of 1,2-dimethyl-pyrazolium salts. 2-Unsubstituted 1,3-dithiolylium salts are easily deprotonated by nucleophilic attack of hydrogen. The intermediate carbene easily undergoes dimerization. Hydrogen exchange can also occur (Scheme 23) (80AHC(27)15l). 

Substituents on the isothiazole ring are a little more reactive, especially in the 5-position. In cationic rings reactivity is much higher, e.g. for substituents in 1,2-dithiolylium salts. 

Proton loss from alkyl groups a or 7 to a cationic center in an azolium ring is often easy. The resulting neutral anhydro bases or methides (cf. 381) can sometimes be isolated they react readily with electrophilic reagents to give products which can often lose another proton to give new resonance-stabilized anhydro bases. Thus the trithione methides are anhydro bases derived from 3-alkyl-l,2-dithiolylium salts (382 383) (66AHC(7)39). These... 

Analogous open-chain precursors also lead readily to 1,3-dithiolylium salts. S-a-Oxoalkyl thioesters such as (20) on treatment with perchloric acid in glacial acetic acid and HaS undergo ready cyclization to the 1,3-dithiolylium perchlorate (22) (66AH0.7)39). The oxoalkyl dithioesters (21) are probably intermediates in this cyclization as they themselves undergo cyclization with warm 70% perchloric acid or sulfuric acid (80AHC(27)15l). 

Dithiolylium salts (483) may be converted into pyrazoles, pyrazolium salts and isothiazoles depending on the type and degree of substitution of the nitrogen source. 

Phenyl-l,2-dithiolylium salt (483) with hydrazine, methylhydrazine or phenylhydrazine yielded the corresponding pyrazole (485) via the intermediates (484a-c). The ring-fused system (486) is a convenient source of the ring-fused pyrazole (487) when treated with hydrazine (see Chapter 4.31). 

Dithiolylium salts, 3-alkoxy-nucleophilic reactions, 6, 794 synthesis, 6, 809... 

Dithiolylium salts, 3-alkyl-anhydro bases, 5, 89 condensation reactions, 4, 799 deprotonation, 6, 793... 

Dithiolylium salts, 5-alkyl-3-alkylthio-self condensation, 6, 799... 

Dithiolylium salts, 3-alkylthio-mass spectra, 6, 786 oxidation, 5, 103... 

Dithiolylium salts, 3,5-diamino-applications, 6, 810 deprotonation, 6, 793 reactions... 

Dithiolylium salts, 3-phenyl-nitration, 5, 91 theoretical studies, 6, 784... 

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