Kowalski rearrangement

Since sUyl ynol ethers have an electron-rich triple bond, they are useful for Lewis acid catalyzed synthetic reactions. Lithium ynolates 175 are silylated by TIPSCl or TIPSOTf and TBSCl to afford the corresponding silyl ynol ethers 176 and 177, which are thermally stable and isolable, but sensitive toward acids (equation 71) . See also equations 9 and 10 in Section ll.C. An experimentally improved procedure for the purification of 176 derived from Kowalski s method is described. Lithium ynolate derived from Julia s method is also used for the preparation of 176. TMSCl and TESCl provide silyl ketenes 179, however, by C-silylation. These small silyl chlorides primarily gave the silyl ynol ethers 178, but, upon warming the reaction mixture, isomerization to the more stable silyl ketenes takes place. The soft electrophilic silyl chlorides like PhsSiCl afford silyl ketenes. Disi-lyl ynol ethers, prepared from ynolate dianions, are rearranged to disilylketenes mediated by salts . 

Taylor, M. S., Jacobsen, E. N. Highly enantioselective catalytic acyl-Pictet-Spengler reactions. J. Am. Chem. Soc. 2004, 126, 10558-10559. Kowalski, P., Mokrosz, J. L. Structure and spectral properties of P-carbolines. Part 9. New arguments against direct rearrangement of the spiroindolenine intermediate into P-carboline system in the Pictet-Spengler cyclization. An MNDO approach. Bull. Soc. Chim. Belg. 1997, 106, 147-149. 

Kowalski et employed dibromomethyllithium (prepared in situ) to prepare an a-bromo ketone enolate at low temperatures. At higher temperatures and under extremely basic conditions, this enolate rearranged to give an ynolate. A mixture of 1,3-cyclohexadiene and LITMP transformed the ynolate to an aldehyde (E)-enolate (Scheme 19). 

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