Benzodithiolylium tetrafluoroborate

Sodium azide can react with 1,3-benzodithiolylium tetrafluoroborate (32) in acetonitrile to form the azide (38) which on treatment with trityl tetrafluoroborate yields trityl azide and (32) (80JOC2024). The last step of this reaction does not lead to the expected 2-azido-l,3-benzodithiolylium salt. 

With sodium in liquid ammonia, 1,3-benzodithiolylium tetrafluoroborate undergoes a reductive cleavage to benzene-1,2-dithiol (76S471). 

Benzodithiolylium tetrafluoroborate can be transformed into the phosphonium salt (54). Reaction with carbonyls, in the usual way, affords 1,4-benzodithiafulvenes. ... 

Benzodithiolylium tetrafluoroborate (78) upon reaction with an excess of 2,6-dichlorophenol finally affords (79) (Equation (11)) <77CL789>. 

Organocatalytic S l-type reactions with carbenium ions have not been employed in natural product synthesis, as they are of limited utility. A more effective and useful reaction for use in natural product synthesis has been described by the Cozzi group, which explores the chemistry of the readily available benzodithiolylium tetrafluoroborate 1 in organocatal3d ic enantio-selective reactions (Scheme 18.1). ... 

The use of enamine catalysis in the enantioselective a-functionalization of carbonyl compounds has been reviewed, including aldol, Mannich, and alkylation processes," and a short review has examined enantioselective a-alkylation of aldehydes Benzodithiolylium tetrafluoroborate (133) is a water-stable salt and can be added enantioselectively to aldehydes at the a-position in the presence of simple chiral organocatalysts, giving the corresponding alcohol. The sulfurs can be readily cleaved with H2/Raney Ni, rendering the process a formal tf-methylation of aldehydes." a ,/3-Unsaturated aldehydes undergo enantioselective a- and y-alkylation via dien-amine activation, using a diarylprolinol TMS ether as catalyst." ... 

Very recently, Cozzi et al. successfully demonstrated the application of this methodology for the a-alkylation of the formyl group to enohzable aldehydes. This was achieved by a reaction of benzodithiolylium tetrafluoroborate (a stabilized carbenium ion) in the presence of several different substituted imidazolidin-4-ones [48]. After reductive removal of the benzodithiol group access to chiral a-branched primary alcohol is given. Using this method optically pure arundic acid is obtained by a three-step synthesis. 

Condensation of acetic or benzoic esters with benzene-1,2-dithiol in the presence of tetrafluoroboric acid/ether complex yields 2-methyl- or 2-phenyl-1,3-benzodithiolylium salts, respectively (77S263). 

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