Addition of Nitrosyl Chloride to Trimethylsilyl Enol Ethers. A New General Method for Nitrosation of Carbonyl Compounds

Addition of nitrosyl chloride to trimethylsilyl enol ethers 1 in dichloromethane at −10 to −15° gives good yields of α-oximinocarbonyl compounds 2. In the case of aldehydes, these initial products are unstable, but may be trapped by hydroxylamine as the glyoximes 3. The silyl ether of cyclohexanone 1h yields 2,6-dioximinocyclohexanone (4) upon treatment with excess NOCl, whereas with 1 equiv of NOCl the unstable nitroso dimer 5 is formed. Similarly, the silyl derivatives of esters, lactones, and carboxylic acids are directly converted to α-oximino esters and acids. The results are explained by initial addition of NOCl to the silyl enol ether double bond, followed by elimination of trimethylsilyl chloride and tautomerization to the oxime.