[68725-14-4] · C13H27F3O3SSn · Tri-n-butyltin Trifluoromethanesulfonate · (MW 439.18)
Physical Data: mp 41-43 °C; bp 155-167 °C/0.08 mmHg.
Solubility: freely sol polar and nonpolar organic solvents.
Preparative Methods: by analogy to the preparation of trialkyltin carboxylates,5 tribuyltin trifluoromethanesulfonate is prepared from Bis(tri-n-butyltin) Oxide and either Trifluoromethanesulfonic Acid (with subsequent removal of water) or Trifluoromethanesulfonic Anhydride,2 as in eq 1.
The following procedure is quite convenient: freshly distilled trifluoromethanesulfonic anhydride6 is caused to react with an equal molar amount of tributyltin oxide cooled at 20 °C under nitrogen. When the exothermic reaction completely subsides, the flask is set up for a short-path distillation and the resulting red oil is distilled at about 0.1 mmHg. The distillate is collected without cooling to prevent crystallization of the product in the condenser. Alternatively, this reagent can be prepared in situ by the action of trifluoromethanesulfonic acid on Tri-n-butylstannane in benzene or dichloroethane.4
Handling, Storage, and Precautions: this reagent is deliquescent. Therefore it is best handled as a solution in benzene, ether, or hexane, stored at room temperature under nitrogen. Solutions can be dried with 4Å molecular sieves. As with certain other trialkyltin electrophiles, tributyltin trifluoromethanesulfonate is foul smelling. The toxicity of this class of compounds has been described.7 Use in a fume hood.
The powerful electrophilic property of this reagent makes it particularly attractive for the conversion of vinylcuprates and vinylalanes into vinylstannanes. For example, the reaction of vinyl heterocuprates8 with this reagent occurs readily to give the corresponding (Z)-vinylstannane, even at -78 °C (eq 2). Stannylation of vinylalanes9 occurs readily to give the corresponding vinylstannane (eq 3). Complementary methods are available for the preparation of both (Z)-2 and (E)-vinylstannanes.1,3 The configuration of the vinylstannane is controlled at the vinylaluminum stage: treatment of Propargyl Alcohol with Lithium Aluminum Hydride followed by tributyltin trifluoromethanesulfonate affords the (Z)-allyl alcohol, whereas if the addition of LiAlH4 is followed by NaOMe and then the reagent, the (E)-allyl alcohol results (eq 4).1
The (E)-vinylstannane also results when the alkyne is treated sequentially with Diisobutylaluminum Hydride, Methyllithium, and then the title reagent.3 For example, treatment of 1-octyne with DIBAL in hexane followed by MeLi and then the reagent afforded (E)-1-tributylstannyl-1-octene in good yield (eq 5).
The title reagent is also suitable for the preparation of allylstannanes from allyllithium reagents,10 and vinylstannanes from vinyllithium reagents.11
This triflate is a catalyst in the hydrostannation of aldehydes and ketones by tributyltin hydride.4 Treatment of aldehydes and ketones with one equiv of Bu3SnH in benzene or dichloroethane in the presence of 20% of the reagent afforded the corresponding primary or secondary alcohol in high yield. Using this system, aldehydes are preferentially reduced in the presence of methyl ketones (ca. 99:1). In addition, the reagent can be employed as a cocatalyst with PdCl2(PPh3)2 in the 1,4-reduction of enone systems (eq 6).
The title reagent catalyzes the rapid and stereospecific cyclization of certain chiral arylsulfanyl lactones to the corresponding optically pure g-butyrolactones (eq 7).12
Thomas M. Eckrich
Eli Lilly and Company, Lafayette, IN, USA