PALLADIUM-CATALYZED STILLE COUPLINGS WITH FLUOROUS TIN REACTANTS

A new class of ''fluorous'' aryl tin reactants was investigated for us e in the Stille coupling. Fluorous compounds partition into a fluoroca rbon (fluorous) phase in a fluorous/organic extraction. The coupling o f tris[(perfluorohexyl)ethyl]phenyl tin [(C6F13CH2CH2)(3)SnPh] with br omobenzene occurs smoothly in DMF/THF (1/1) at 80 degrees C in the pre sence of a catalytic amount of PdCl2(PPh3)(2) and 3 equiv of LiCl. Par titioning between CH2Cl2 and FC-72 (a mixture of perfluorohexanes) pro vided biphenyl in 90% yield from the organic phase and tris[(perfluoro hexyl)ethyl]tin chloride in >90% yield from the fluorous phase. The ti n chloride was reacted with phenylmagnesium bromide to regenerate the starting tin reactant. A study to optimize reaction conditions is desc ribed, and the scope of the method is illustrated with 20 coupling rea ctions. The beneficial effect of lithium choride is an unusual feature of the reaction, but it also promotes the formation of some fluoroalk yl-coupled products. These can be suppressed by adding CuI. The paper describes a prototypical example of how to render a tin reactant fluor ous. This process should be advantageous in small-and large-scale synt hesis, as well as in automated synthesis.