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

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.