01559nas a2200157 4500008004100000245015100041210006900192260000800261300001400269490000700283520091300290100002401203700002801227700002201255856012401277 2018 eng d00aBismuth(III)-catalyzed cycloisomerization and (hetero)arylation of alkynols: simple access to 2-(hetero)aryl tetrahydrofurans and tetrahydropyrans0 aBismuthIIIcatalyzed cycloisomerization and heteroarylation of al cMAY a3229-32400 v163 a2-(Hetero)aryl tetrahydrofurans and tetrahydropyrans were successfully synthesized using Bi(OTf)(3)-catalyzed hydroalkoxylation (cycloisomerization) of alkynols (via 5 or 6 exo-dig cyclization) and intermolecular (hetero)arylation. This reaction involves a highly efficient cascade process, where initially the alkynol undergoes a cycloisomerization step via activation of the triple bond and generates the oxocarbenium ion, which subsequently participates in the (hetero)hydroarylation step with electron-rich arenes. Simple to complex suitably functionalized alkynols (4-pentyn-1-ols and 5-hexyn-1-ols) and electron-rich aromatic compounds were found to be reliable substrates in this cascade transformation and furnished a wide range of oxygen heterocycles. This practical tandem process provides a means to build libraries related to pharmacologically active molecules and natural product like scaffolds.1 aNakate, Ashwini, K.1 aPratapure, Madhukar, S.1 aKontham, Ravindar uhttps://library.ncl.res.in/content/bismuthiii-catalyzed-cycloisomerization-and-heteroarylation-alkynols-simple-access-201176nas a2200169 4500008004100000022001400041245014500055210006900200260000900269300001400278490000700292520050300299100002600802700002600828700002200854856013000876 2021 eng d a1477-052000aBismuth(iii)-catalyzed bis-cyclization of propargylic diol-esters: a unified approach for the synthesis of [5,5]- and [6,5]-oxaspirolactones0 aBismuthiiicatalyzed biscyclization of propargylic diolesters a u cAUG  a6618-66220 v193 aHerein we disclose an unprecedented intramolecular cascade strategy for the construction of alpha,beta-unsaturated [5,5]- and [6,5]-oxaspirolactones that capitalizes on the pi-electrophilic Lewis acid-catalyzed 5-exo-dig or 6-exo-dig mode of cyclization of propargylic diol esters, followed by dehydration and spirolactonization steps. Moreover, semi-protected substrates also delivered the respective oxaspirolactones with the same ease and in appreciable yields under optimal reaction conditions.1 aKambale, Digambar, A.1 aBorade, Balasaheb, R.1 aKontham, Ravindar uhttps://library.ncl.res.in/content/bismuthiii-catalyzed-bis-cyclization-propargylic-diol-esters-unified-approach-synthesis-5501512nas a2200169 4500008004100000022001400041245015600055210006900211260000800280300001400288490000700302520082800309100002201137700003201159700002201191856012901213 2023 eng d a0022-326300aBi(III)-catalyzed synthesis of substituted furans from hydroxy-oxetanyl ketones: application to unified total synthesis of shikonofurans J, D, E, and C0 aBiIIIcatalyzed synthesis of substituted furans from hydroxyoxeta cMAY a7328-73460 v883 a

We report an improved synthetic protocol for hydroxymethyl-derivedpolysubstituted furans employing Bi-(III)-catalyzed dehydrative cycloisomerizationof alpha-hydroxy oxetanyl ketones. This procedure provides rapidaccess (within 5 min) to highly substituted furans with exceptionalfunctional group diversity, excellent yields, generality, scalability,and operationally simple reaction conditions. Further, it demonstratedthe utility of this method in the first enantioselective total synthesisof furyl-hydroquinone-derived biologically potent natural productsshikonofurans J, D, E, and C in seven linear steps, starting fromreadily available building blocks of 2,5-dihydroxy acetophenone and3-oxetanone employing chiral-phosphoric acid (TRIP)-catalyzed asymmetricprenylation as a key step to induce the chirality.

1 aKataria, Priyanka1 aSahoo, Shubhranshu, Shekhar1 aKontham, Ravindar uhttps://library.ncl.res.in/content/biiii-catalyzed-synthesis-substituted-furans-hydroxy-oxetanyl-ketones-application-unified01562nas a2200217 4500008004100000022001400041245014000055210006900195260000900264300001100273490000800284520076300292653002101055653002201076653002501098653002801123653002101151100002801172700002201200856012201222 2023 eng d a0040-403900aBismuth(III)-catalyzed cascade condensation of alkynyl alcohols with terminal alkynes: a facile construction of propargyl cyclic ethers0 aBismuthIIIcatalyzed cascade condensation of alkynyl alcohols wit cJAN  a1542740 v1143 a

Herein, we report a Bi(OTf)3-catalyzed cascade condensation between alkynols (particularly pent-4-yn-1ols and hex-5-yn-1-ols) and terminal alkynes (aryl alkynes) to facile access to diverse propargyl cyclic ethers (2 alkynyl tetrahydrofurans and 2 alkynyl tetrahydropyrans). This simple and efficient cascade transformation proceeds through initial intramolecular hydroalkoxylation of alkynols to give corresponding cyclic enol ethers (via exo-dig or endo-dig mode of ring-closure) followed by hydroalkynylation. Costeffective, naturally abundant, green Lewis acid catalysis, ambient reaction conditions, short reaction times, good substrate scope, and high yields are salient features of this strategy.(c) 2022 Elsevier Ltd. All rights reserved.

10aAlkynyl alcohols10aBismuth catalysis10aCascade condensation10aPropargyl cyclic ethers10aTerminal alkynes1 aPratapure, Madhukar, S.1 aKontham, Ravindar uhttps://library.ncl.res.in/content/bismuthiii-catalyzed-cascade-condensation-alkynyl-alcohols-terminal-alkynes-facile01319nas a2200229 4500008004100000022001400041245015600055210006900211260000900280300001200289490000700301520049200308653002900800653001300829653001400842653001100856100002300867700002600890700002500916700002200941856012600963 2024 eng d a1477-052000aBi(OTf)3-promoted cascade annulation of hydroxy-pyranones and unsaturated γ-ketoesters for the construction of polycyclic bridged pyrano-furopyranones0 aBiOTf3promoted cascade annulation of hydroxypyranones and unsatu cJAN  a496-5000 v223 a

An efficient protocol for constructing complex three dimensional polycyclic bridged chromano-furopyranones and pyrano-furopyranones (closely related to bioactive natural products) via bismuth(III)-catalyzed cascade annulation of hydroxy-pyranones and unsaturated gamma-ketoesters is presented. This process involves intermolecular Michael addition, intramolecular hemiketalization, lactonization, formation of one C-C bond and two C-O bonds, rings, and contiguous stereocenters.

10a1 3-Dicarbonyl Compounds10aalkynols10aCoumarins10aFungus1 aRathod, Akshay, B.1 aBorade, Balasaheb, R.1 aSambherao, Pooja, I.1 aKontham, Ravindar uhttps://library.ncl.res.in/content/biotf3-promoted-cascade-annulation-hydroxy-pyranones-and-unsaturated-%CE%B3-ketoesters01990nas 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

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 & 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.

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