Stille Reactions with Tetraalkylstannanes and Phenyltrialkylstannanes in Low Melting Sugar – Urea - Salt Mixtures

Abstract

The transfer of simple alkyl groups in
Stille reactions usually requires special solvents
(HMPA) or certain organotin reagents (stannatranes,
monoorganotin halides) to be efficient.
Using low-melting mixtures of sugar, urea and inorganic
salt as solvent, a fast and efficient palladiumcatalyzed
alkyl transfer with tetraalkyltin reagents
was observed. The high polarity and nucleophilic
character of the solvent melt promotes the reaction.
Stille biaryl synthesis using electron-poor and electron-
rich aryl bromides proceeds with quantitative
yields in the sugar-urea-salt melt. Catalyst loading
may be reduced to 0.001 mol% and the catalyst
melt mixture remains active in several reaction
cycles. Showing the same or improved performance
for Stille reactions than organic solvents and allowing
a very simple work up, sugar-urea-salt melts are
a non-toxic and cheap alternative reaction medium
available in bulk quantities for the catalytic process.