01990nas a2200205   4500008004100000022001400041245015200055210007200207260000900279300001600288490000600304520119700310100002501507700002401532700002101556700001701577700002601594700002201620856014201642       2024                        eng d  a2470-134300aBronsted acid-promoted cyclodimerization of α,β-unsaturated γ-ketoesters: construction of fused pyrano-ketal-lactones and γ-ylidene-butenolides0 aBronsted acidpromoted cyclodimerization of αβunsaturated γketoes  cAPR   a19859-198780 v93 a<p>
	Unprecedented MsOH-promoted diastereoselective cascade dimerization and intramolecular lactonization of readily accessible alpha,beta-unsaturated gamma-ketoesters are presented. The results obtained in this work, control experiments, and density functional theory (DFT) calculations suggested that the initial enolization and E to Z isomerization/equilibration of olefin (C=C) of substrate alpha,beta-unsaturated gamma-ketoesters give a Z-isomer preferentially over an E-isomer. Subsequently, the Z-isomer undergoes intermolecular annulation with alpha,beta-unsaturated gamma-ketoesters via domino Michael addition/ketalization/lactonization steps to furnish fused tetracyclic pyrano-ketal-lactone. However, the Z-isomer prefers intramolecular trans-esterification in a competing pathway and gives bicyclic gamma-ylidene-butenolide. The key features of this work include simple Br &amp; oslash;nsted acid catalysis, the formation of three bonds, two rings, and three contiguous stereogenic centers in a single step, DFT calculations, and the assignment of relative stereochemistry through X-ray diffraction (XRD) and two-dimensional (2D) nuclear magnetic resonance (NMR) analyses.</p>
1 aVinodkumar, Ramavath1 aNakate, Ashwini, K.1 aSharma, Himanshu1 aVanka, Kumar1 aKrishna, Gamidi, Rama1 aKontham, Ravindar  uhttps://library.ncl.res.in/content/bronsted-acid-promoted-cyclodimerization-%CE%B1%CE%B2-unsaturated-%CE%B3-ketoesters-construction-fused