An expedient and stereoselective synthesis of alkenyl nonaflates from silyl enol ethers: Optimization, scope and limitations

The fluoride-catalysed reaction between silyl enol ethers 1 and nonafluorobutanesulfonyl fluoride (NfF) has been optimized, resulting in an expedient synthesis of the corresponding alkenyl nonaflates 3. Tetra-n-butylammonium fluoride, dried either with molecular sieves or with potassium fluoride, and potassium fluoride in the presence of dibenzo-18-crown-6 were the best and most practical catalysts for this process. The reaction allows the synthesis of a wide variety of cyclic and acyclic alkenyl nonaflates 3 in good to excellent yields. For E/Z isomeric alkenes the configuration of the double bond is essentially retained. Remarkably, enolates derived from methyl ketones also provide C-sulfonylation products 4 as a side product; the desired alkenyl nonaflates 31 and 3m could, however, be prepared in good yields by further optimization. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.