1.3- Dithiolylium tetrafluoroborate

Several variations of this general procedure have been described. The functionalized dithiocarbamate (23) on heating with a mixture of phosphorus pentasulfide and tetrafluoroboric acid gave the 2-amino-substituted 1,3-dithiolylium tetrafluoroborate (24) in moderate to good yield (69CPB1924). 

When the addition is complete, anhydrous diethyl ether (about 200 mL) is added. The near-white salt, 1,3-dithiolylium tetrafluoroborate,12 is collected on a Buchner funnel, washed with anhydrous diethyl ether, and dried under nitrogen. The 1,3-dithiolylium tetrafluoroborate (28 g, 0.15 mole) from the precious step is dissolved in acetonitrile (100 mL) in a 500-mL Erlenmeyer flask. While the solution is stirred magnetically at 0°, triethylamine is added until the formation of yellow crystals becomes obvious (about 50 mL). Another quantity of triethylamine (about 10 mL) is added and stirring is continued for 10 minutes. Water (approximately 300-400 mL) is added to precipitate the product, which separates as yellow-orange crystals. The solid is collected on a Buchner funnel, washed with water, and dried under nitrogen. The yield of crude product is 15.0 g (0.0736 mole), which corresponds to an 82% overall yield based on the starting 2-(methylthio)-l,3-dithiolylium iodide. 

Furthermore, cyclopentenedione (62) reacts with 1,3-dithiolylium tetrafluoroborate (1) in aqueous ethanol with formation of compound (63) which can be easily oxidized using 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to produce the dithiafulvalene derivative (64) (77CL77). 

In an analogous manner, from 1,3-dithiolylium tetrafluoroborate (88) and 2-cyclopentene-l,4-dione the product (89) was formed, which was oxidized using ddq to yield the dithiafulvalene derivative (90) (Scheme 21) <77CL77>. 

Benzo-1,3-ditellurolylium tetrafluoroborate 76 turned out to be the first preparatively isolated salt of a heterocyclic carbocation containing two tellurium atoms in a ring (91UP3). The synthesis of 76 was carried out, similar to its sulfur analog benzo- 1,3-dithiolylium boron tetrafluoride (76BCJ3567), by treatment of a solution of 2-butoxybenzo-l,3-ditellurole in acetic anhydride with 2 equivalents of HBF4. 

Alkylthio-l,3-dithioles (190) react with trityl tetrafluoroborate in acetonitrile to produce the 1,3-dithiolylium salts (54) in high yields (80AHC(27)15l). 

Oxoalkyl dithioesters 259 are cyclized by perchloric acid to dithiolylium salts 260 (Scheme 127) <1980AHC(27)151>. Similarly, dithiocarbamate 261 with phosphorus pentasulfide and tetrafluoroboric acid gives the 2-amino-l,3-dithioly-lium tetrafluoroborate 262 (Scheme 128) <1969CPB1924>. 

Utilization of the conjugate bases of 3-alkyl-l,2-dithiolylium and 3-alkyl-1,2-diselenolylium salts as precursors for sulfur or selenium containing 6,6a2 -triheterapentalenes is a widely used synthetic method. In a slight variation bis-(12, 2-diselenol-l-ylium) salts have been used as precursors. 3-Alkyl-substituted diselenolylium tetrachloroferrates (78) give 6,6aA -diselena-l,2-diazapentalenes (79) upon treatment with benzenediazonium tetrafluoroborate (Equation (23)). The mechanism involves the deprotonation of the 3-methyl substituent followed by rapid electrophilic substitution <93HAC337>. 

The synthesis of enamino-thioketones has been pursued mainly by the groups of Quiniou and Usov. " Traditional methods employed include reaction of P4S10 with enamino-ketones, reaction of amines with 1,2-dithiolylium salts, and transamination of enamino-thioketones, > which was used to prepare the previously unknown simple compound (18). Access to thioamide vinylogues has also been achieved through the reaction of a monothio-/3-diketone with ammonia, and, for 3-amino-2-arylindene-l-thiones (19), by reaction of enamino-imines with P4S10 or sodium hydrosulphide or by reaction of 1-imino-2-aryl-2-alkyloxyindene tetrafluoroborates with sodium hydrosulphide. ... 

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