Solvolysis of asymmetric homoallylic triflates bearing a terminal stannyl substituent gives disubstituted cyclopropanes and bicyclopropanes bearing differentiated termini in high enantiopurity.
Download full-text PDF |
Source |
---|---|
http://dx.doi.org/10.1039/b412811g | DOI Listing |
ACS Omega
May 2024
Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India.
Unprecedented MsOH-promoted diastereoselective cascade dimerization and intramolecular lactonization of readily accessible α,β-unsaturated γ-ketoesters are presented. The results obtained in this work, control experiments, and density functional theory (DFT) calculations suggested that the initial enolization and to isomerization/equilibration of olefin (C=C) of substrate α,β-unsaturated γ-ketoesters give a -isomer preferentially over an -isomer. Subsequently, the -isomer undergoes intermolecular annulation with α,β-unsaturated γ-ketoesters via domino Michael addition/ketalization/lactonization steps to furnish fused tetracyclic pyrano-ketal-lactone.
View Article and Find Full Text PDFChem Commun (Camb)
May 2024
Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
Progress towards the total synthesis of the macrolide natural product anthracimycin is described. This new approach utilises an intermolecular Diels-Alder strategy followed by epimeirsation to form the key -decalin framework. The route culminates in the stereoselective synthesis of an advanced tricyclic lactone intermediate, containing five contiguous sterogenic centres with the correct relative and absolute stereochemistry required for the anthracimycin core motif.
View Article and Find Full Text PDFOrg Lett
October 2023
Graduate School of Pharmaceutical Sciences, Chiba University, Chiba 260-8675, Japan.
The enantioselective total syntheses of (-)-silicine and (-)-20-episilicine, which contain a chiral piperidine with three contiguous chiral centers (-ring) and a strained seven-membered ring (-ring) attached to an indole, were achieved. The key steps of these syntheses included a chiral secondary amine-catalyzed formal aza-[3 + 3] cycloaddition reaction and Lewis acid-mediated irreversible ring-closing reaction. In addition, the stereochemistry at C20 was controlled at a later stage in the syntheses.
View Article and Find Full Text PDFOrg Lett
September 2023
University of Texas at Austin, Department of Chemistry, Austin, Texas 78712, United States.
The C28-C41 side-chain of the proposed structure of neaumycin B, which encompasses a contiguous stereohextet, is prepared in 8 steps (longest linear sequence). Convergency is maximized via Williams' Felkin-Anh-selective triorganozincate-mediated vinylation of an α,β-stereogenic aldehyde. The relative stereochemical assignment of the C33-C35 stereotriad was accomplished via the C NMR analysis of the related acetonide.
View Article and Find Full Text PDFJ Am Chem Soc
June 2023
College of Chemistry, Central China Normal University, 152 Luoyu Road, Wuhan, Hubei 430079, China.
Photocatalytic [3 + 2] cycloadditions and control of stereochemistry have remained a substantial challenge, particularly in the context of heterocycle synthesis; sporadic successful examples have involved enantioselective [3 + 2] photocycloaddition between redox-active direct group-containing cyclopropanes and alkenes for creation of cyclopentanes. Herein, we report a cooperative catalytic system comprising a chiral nickel Lewis acid catalyst and an organic photocatalyst fueled by visible-light irradiation that allows for the hitherto elusive asymmetric [3 + 2] photocycloaddition of β-keto esters with vinyl azides under redox-neutral conditions. This protocol enables highly enantioselective construction of polycyclic densely substituted 3,4-dihydro-2-pyrrole heterocycles featuring two contiguous tetrasubstituted carbon stereocenters, including a useful chiral ,-ketal motif that is not easily accessible with other catalytic methods.
View Article and Find Full Text PDFEnter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!