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-201579nas a2200205 4500008004100000022001400041245014300055210007100198260000800269300001200277490000600289520081600295100002401111700002201135700001801157700002601175700001701201700002201218856013301240 2022 eng d a2052-412900aSilver-catalyzed [3 + 3]-annulation cascade of alkynyl alcohols and α,β-unsaturated ketones for the regioselective assembly of chromanes0 aSilvercatalyzed 3 3annulation cascade of alkynyl alcohols and αβ cJAN a802-8090 v93 aAn unprecedented Ag(i)-catalyzed [3 + 3]-annulation of alkynyl alcohols (5-hexyn-1-ols) and α,β-unsaturated ketones is reported to construct simple to complex chromanes. This transformation begins with hydroalkoxylation of alkynol through C–C triple bond activation to give cyclic-enol ether, followed by intermolecular 1,4-addition and intramolecular 1,2-addition of enol ethers onto the enone and oxidative aromatization or Grob-type elimination steps. Facile reaction conditions, broad substrate scope, good to excellent yields, and atom economy are the salient features of this protocol. Isolation of the active pyran-tethered cyclohexadiene reaction intermediate, additional supporting experiments, and DFT calculations strongly support the experimental findings and corroborate our proposed mechanism.1 aNakate, Ashwini, K.1 aThorat, Sagar, S.1 aJain, Shailja1 aKrishna, Gamidi, Rama1 aVanka, Kumar1 aKontham, Ravindar uhttps://library.ncl.res.in/content/silver-catalyzed-3-3-annulation-cascade-alkynyl-alcohols-and-%CE%B1%CE%B2-unsaturated-ketones01990nas 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-fused01148nas a2200193 4500008004100000022001400041245015100055210006900206260000800275300001400283490000700297520039900304100002400703700002200727700002500749700002600774700002200800856013200822 2024 eng d a1359-734500aDivergent access to polycyclic spiro- and fused-N,O-ketals through Bi(OTf)3-catalyzed [4+2]-annulation of cyclic N-sulfonyl ketimines and alkynols0 aDivergent access to polycyclic spiro and fusedNOketals through B cJAN a1144-11470 v603 a

Bismuth(iii) triflate-catalyzed [4+2]-annulation of cyclic N-sulfonyl ketimines (derived from saccharin) and alkynyl alcohols (4-pentyn-1-ols and 5-hexyn-1-ols) has been reported. This cascade annulation provides a diverse array of polycyclic spiro-and-fused N,O-ketals with excellent substrate scope, good isolated yields, and diastereoselectivities under mild reaction conditions.

1 aNakate, Ashwini, K.1 aKataria, Priyanka1 aSambherao, Pooja, I.1 aKrishna, Gamidi, Rama1 aKontham, Ravindar uhttps://library.ncl.res.in/content/divergent-access-polycyclic-spiro-and-fused-no-ketals-through-biotf3-catalyzed-42-annulation01484nas a2200181 4500008004100000022001400041245012600055210006900181260000800250300001400258490000700272520079700279100002501076700002401101700002601125700002201151856012901173 2024 eng d a1523-706000aReady access to [5,6,5]-Trioxa-spiro and fused ketals via ag-catalyzed cascade annulation of 4-pentyn-1-ols and aldehydes0 aReady access to 565Trioxaspiro and fused ketals via agcatalyzed  cAUG a7116-71210 v263 a

In this study, we unveil the versatility of 4-pentyn-1-ols as carbonyl surrogates for the unprecedented synthesis of diverse oxygen heterocycles, including [5,6,5]-bis-spiroketals (trioxadispiroketals) and [5,6,5]-furano-spiroketals related to bioactive natural products. These reactions commence with the pi-activation-induced intramolecular hydroalkoxylation of 4-pentyn-1-ols, yielding cyclic enol ethers, which undergo subsequent three-component annulation with aldehydes in a [2+2+1+1] fashion, resulting in the formation of [5,6,5]-bis-spiroketals. Notably, the distinctive steric features of alkynyl alcohols, particularly those with a secondary or tertiary alcohol functionality, dictate divergent reaction pathways, leading to the formation of [5,6,5]-furano-spiroketals.

1 aVinodkumar, Ramavath1 aNakate, Ashwini, K.1 aGamidi, Rama, Krishna1 aKontham, Ravindar uhttps://library.ncl.res.in/content/ready-access-565-trioxa-spiro-and-fused-ketals-ag-catalyzed-cascade-annulation-4-pentyn-101096nas a2200181 4500008004100000022001400041245017100055210006900226260000900295300001200304490000700316520036400323100002500687700002400712700002600736700002200762856013000784 2025 eng d a1359-734500aAgOTf-catalyzed cascade annulation of 5-hexyn-1-ols and aldehydes: enabling the diastereoselective synthesis of [6,6,6]-trioxa-fused ketals and hexahydro-2H-chromenes0 aAgOTfcatalyzed cascade annulation of 5hexyn1ols and aldehydes en cJAN  a973-9760 v613 a

We report the unprecedented diastereoselective synthesis of novel [6,6,6]-trioxa-fused ketals via AgOTf-catalyzed cascade annulation of 5-hexyn-1-ols (with primary or secondary hydroxyl groups) and aldehydes through a [2+2+1+1] pathway. In contrast, 5-hexyn-1-ols with tertiary hydroxyl groups yield hexahydro-2H-chromenes via a [3+1+1+1] pathway.

1 aVinodkumar, Ramavath1 aNakate, Ashwini, K.1 aKrishna, Gamidi, Rama1 aKontham, Ravindar uhttps://library.ncl.res.in/content/agotf-catalyzed-cascade-annulation-5-hexyn-1-ols-and-aldehydes-enabling-diastereoselective