Dimethyl sulfonium fluoroborate

Finally, in contrast to the reactions reported above, 49 reacts131 with dimethyl(methyl-thio)sulfonium fluoroborate (DMTSF) and triethylamine tris(hydrofluoride) in dichlorome-thane to give only 5% of the 1,2-addition product 122. The main products, present in 73 27 ratio, are the exo-exo and endo-exo adducts 123 and 124, formed by exclusive exo attack of the electrophile on the double bond, followed by transannular -participation in the intermediate bridged cation and final addition of fluoride to the nortricyclic cation from both the exo or endo side (equation 120). 

Examples of 5-exo cyclizations in which the hydroxy group is constrained by a five-membered ring are shown by equation (53). The stereoselectivity in these cyclizations ranges from quite high in iodocy-clization (9 1 in H2O and >20 1 in CH2CI2) to only moderate (2—3 1) with mercury and phenylselenenyl chloride. P This type of cyclization has been widely applied to synthesis of prostacyclins.146 Similar cyclizations with dimethyl(methylthio)sulfonium fluoroborate have been reported recently.35... 

Allylstannanes are much better nucleophiles for dithioacetals than allylsilanes, and dimethyl(methyl-thio)sulfonium fluoroborate is a particularly good catalyst in this reaction. The reaction has been used tellingly in a macrocyclization (Scheme 56). ° Monothioacetals also react with allylstannanes, with cleavage of either the carbon-oxygen or the carbon-sulfur bond, depending upon the choice of Lewis acid (Scheme 57).Sugar thioacetals react in the same way (Scheme 58), but with the opposite anomeric stereoselectivity from that of the corresponding radical chain substitution. ... 

In the reaction of enol silyl ethers with a-chloro sulfides (e.g. 101), TiCU or ZnX2 appears to be the Lewis acid of choice." When dithioacetals" are used as the electrophiles, FeCb or dimethyl(methyl-thio)sulfonium fluoroborate (DMTSF 102) have been used successfully as the initiator for the condensations with enol silyl ethers. For example, the intramolecular reactions of (103) induced by 1 equiv. of DMTSF lead to good yields of the cyclization products. ... 

Trost, B.M., and E. Murayama Dimethyl(methylthio)sulfonium Fluoroborate. A Chemoselective Initiator for Thionium Induced Cyclizations. J. Am. Chem. Soc., 103, 6529 (1981). 

Trost BM, Shibata T. Nucleophilic attack of olefins initiated by dimethyl(methylthio)sulfonium fluoroborate (DMTSF). Azasulfenylation. J. Am. Chem. Soc. 1982 104 3225-3228. 

This reaction is an equilibrium and it may be necessary in making sulfonium salts from less reactive sulfides (sterically hindered ones, for example) to use more powerful alkylating agents with non-nucleophilic counterions, for example MesO BFj, trimethyloxonium fluoroborate (also known as Meerwein s salt). The sulfur atom captures a methyl group from O, but the reverse does not happen and the BFj anion is not a nucleophile. Not only is dimethyl ether a poor nucleophile, it is also a gas and is lost from the reaction mixture. The same principle is used to make sulfides from other sulfides. 

Related Reagents. Dimethyl(methylthio)sulfonium Fluoro-borate (DMTSF) Dimethyl(methylthio)sulfonium Tetra-fluoroborate, Methylsulfenyl Trifluoromethanesulfonate, Methyl Trifluoromethanesulfonate, (V-Iodosuccinimide (with Triflic Acid). 

Trimethylthio)methyl fluoroborate (CgH )2Te Thiophene Methylene blue Dimethylpropynyl-sulfonium bromide Sulfoxides, Dimethyl sulfoxide Thiirane 1-oxide Tosylmethylisocyanide Dialkoxysulfuranes... 

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