Nazarov cyclization of divinyl ketones bearing an ester group at the β-position: a remarkable effect of α-substitution and alkene geometry on regioselectivity
these observations are an aromatic group at the α-position with E-olefin geometry provides a cyclopentenone in which the double bond is not in conjugation with an ester, whereas Z-olefin provides a cyclopentenone in which the double bond is in conjugation with an ester; and divinyl ketones bearing an ester group at the β-position and an alkyl group at the α-position with E-olefin geometry provide a cyclopentenone
α,β-Unsaturated ketones can be prepared by reaction of differently substituted β-keto acids and aldehydes. The reaction is carried out under organocatalysis (β-alanine, 0.5 equiv.) and generates the enones with high E selectivity (>95 %). This version of the Verley–Doebner modification of the Knoevenagelreaction is a practical alternative to the classic Horner–Wadsworth–Emmons (HWE) reaction without
1,4-Silatropy of <i>S</i>-α-Silylbenzyl Thioesters: A Convenient Route to Silyl Enol and Dienol Ethers Accompanied by C−C Bond Formation via Thiocarbonyl Ylides
A novel convenient method for the generation of thiocarbonyl ylides from readily accessible starting materials and the first synthetic application of in situ generated ylides in the synthesis of silyl enol and dienol ethers, accompanied by C-C bond formation, is described. Under completely neutral conditions without any catalyst or additive, thermal reactions of S-alpha-silylbenzyl thioesters in sealed tubes at 180 degreesC provided silyl enol and dienol ethers in good to excellent yields with high stereoselectivities. This procedure consists of a multistep reaction in a one-pot process, i.e., 1,4-silatropy of S-alpha-silylbenzyl thioesters to give thiocarbonyl ylides, 1,3-electrocyclization of the ylides to give thiiranes, and the extrusion of sulfur from thiiranes to give silyl enol and dienol ethers.
TRIMITSIS, G. B.;HINKLEY, J. M.;TENBRINK, R.;FABURADA, A. L.;ANDERSON, R.+, J. ORG. CHEM., 1983, 48, N 18, 2957-2962
作者:TRIMITSIS, G. B.、HINKLEY, J. M.、TENBRINK, R.、FABURADA, A. L.、ANDERSON, R.+