Robust and efficient, yet uncatalyzed, synthesis of trialkylsilyl-protected cyanohydrins from ketones

High-yielding cyanosilylation of ketones with NaCN and various chlorotrialkylsilanes in DMSO proceeds smoothly without catalysis to give silyl-protected ketone cyanohydrins. The unique role of DMSO consists in rendering naked cyanide anions that reversibly add to the C=O bond at the rate-determining step followed by fast trapping of the transient tertiary sodium cyanoalcoholates with chlorotrialkylsilanes or in situ generated cyanotrialkylsilanes. Preparatively, the reaction matches the best known catalytic cyanosilylation systems applying expensive Me3SiCN and demonstrates unprecedented efficiency in the synthesis of sterically congested trialkyl silyl-protected cyanohydrins.