Efficient synthesis of cyanohydrin trimethylsilyl ethers via 1,2-chemoselective cyanosilylation of carbonyls

Here we report a sustainable protocol for the cyanosilylation of carbonyl compounds 1a-g and 3a-m using trimethylsilyl cyanide and triphenylphosphine supported on polystyrene as a catalyst under solvent-free conditions. It has been shown that a small amount of the catalyst allows the chemoselective 1,2-addition of trimethylsilyl cyanide to alpha,beta-unsaturated carbonyls 1a-g (5 mol%) and to saturated carbonyls 3a-m (2 mol%). The preparation of cyanohydrin trimethylsilyl ethers 2a-g and 4a-m has been accomplished in good yields (72-99%) and very low E-factor values (5-10). Finally, efficiency has been further improved by setting two different flow procedures that have allowed us to perform the representative preparation of cyanohydrin trimethylsilyl ether 4a on a large scale and with the E-factor of 0.16 or 0.47 consisting in a reduction of 90 or 72% of waste compared to our batch conditions.