[7393-43-3] · C12H20Sn · Tetraallylstannane · (MW 283.03)
Alternate Name: tetraallyltin.
Physical Data: bp 69-70 °C/1.5 mmHg, 87-88 °C/4 mmHg; d 1.179 g cm-3.
Solubility: sol common organic solvents; insol H2O.
Form Supplied in: widely available as a neat liquid. Major impurities are tin chlorides.
Preparative Methods: synthesized by the reaction of Allylmagnesium Bromide with Tin(IV) Chloride in THF.5
Analysis of Reagent Purity: shows one spot in the TLC (hexane) and one peak in the GC. 1H NMR (C6D6) can also be informative.
Purification: pure tetraallyltin is a colorless oil. Commercial tetraallyltin is typically obtained as a slightly yellow oil and used without further purification. Large quantities are purified by fractional distillation. Smaller amounts may be filtered through a plug of silica.
Handling, Storage, and Precautions: is an air and water stable oil. No unusual storage precautions are required. Organostannanes are toxic and should only be used in a well ventilated hood. All glassware should be rinsed in a KOH/EtOH bath during cleaning.
Allyllithium is formed from transmetalation of tetraallyltin with alkyllithiums. Treatment of a hexane or pentane solution of tetraallyltin with 2.0 equiv of n-Butyllithium initiates an exchange reaction which is driven by the precipitation of solid allyllithium.2,6 Removal of solvent by syringe or filtration, followed by washing the allyllithium and dissolution in Et2O, affords a solution of allyllithium which is stable for long periods if stored under an inert atmosphere. An excess of tetraallyltin is employed because transmetalation is an equilibrium reaction which will not proceed to completion.2 Ethereal allyllithium solutions are stable for several months at 0 °C. Because of the need to filter solid allyllithium, this approach has been used only sparingly.
Formation of solid allyllithium can be avoided by treatment of an Et2O solution of tetraallyltin with 4 equiv of Phenyllithium.2 Removal of tetraphenyltin by filtration (filtration is optional) affords a solution of allyllithium, which also contains LiBr from the PhLi preparation and trace levels of Ph4Sn (Ph4Sn is soluble in Et2O at 0.0010 g mL-1 at 20 °C). Allyllithium generated in this manner undergoes conjugate addition with vinyl sulfones in the presence of Potassium t-Butoxide to give the b-allyl sulfone (eq 1).7
A solution of allyllithium has also been generated by the reaction of tetraallyltin with 4 equiv of Methyllithium in Et2O.8 Tetraalkylstannanes must not interfere with the ensuing steps. Reaction of allyllithium generated in this manner with 1-naphthyloxazoline afforded, after acid quench, the trans-dihydronaphthalene (eq 2).8
Disproportionation of tetraallyltin with SnCl4 affords a route to allyltin chlorides.9
Tetraallyltin is a gentle nucleophile capable of transferring one allyl group to ketones, epoxides, and other reactive electrophiles (eq 3).3 Nucleophilicity can be enhanced by reaction in the presence of fluoride,10 or BF3.11 Because only one allyl moiety is transferred, Allyltributylstannane or trimethylallyltin is more commonly used in this reaction.
Tetraallyltin acts as a nucleophile in palladium-mediated cross-coupling reactions (eq 4).12 Because the triallyltin halide byproduct is unreactive, tributylallyltin or trimethylallyltin is more commonly used in this reaction. In an interesting variation, treatment of a-halo ketones with Tetravinylstannane in the presence of catalytic Benzylchlorobis(triphenylphosphine)palladium(II) affords allyl epoxides (eq 5).13
William J. Scott & Alessandro F. Moretto
Bayer Pharmaceuticals Division, West Haven, CT, USA