01311nas a2200181 4500008004100000022001400041245015100055210006900206260000900275300001600284490000700300520059200307100002600899700002600925700002500951700002200976856013100998 2023 eng d a0022-326300aDivergent synthesis of oxepino-phthalides and [5,5]-oxaspirolactones through [2+2+2]- and [2+3]-annulation of alkynyl alcohols with a-ynone-esters0 aDivergent synthesis of oxepinophthalides and 55oxaspirolactones  cAUG  a12597-126120 v883 a

Unmasking the synthetic potential of alkyne functional group of alkynyl alcohols as surrogates of carbonyl compounds, herein we present the first Bronsted acid (TfOH)-catalyzed [2 + 2 + 2]-annulation of 4-pentyn-1-ols (possessing terminal alkyne) with a-ynone-esters to access tricyclic tetrahydro-oxepino-phthalides. Besides, an unprecedented synthesis of a-acetoaryl or a-alkynyl [5,5]-oxaspirolactones has been demonstrated by employing 4-pentyn-1-ols (possessing an internal alkyne) as an annulation partner, which proceeds through a divergent [2 + 3]-annulation pathway.

1 aKambale, Digambar, A.1 aBorade, Balasaheb, R.1 aVinodkumar, Ramavath1 aKontham, Ravindar uhttp://library.ncl.res.in/content/divergent-synthesis-oxepino-phthalides-and-55-oxaspirolactones-through-222-and-23-annulation01989nas a2200205 4500008004100000022001400041245015200055210007200207260000900279300001600288490000600304520119700310100002501507700002401532700002101556700001701577700002601594700002201620856014101642 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 uhttp://library.ncl.res.in/content/bronsted-acid-promoted-cyclodimerization-%CE%B1%CE%B2-unsaturated-%CE%B3-ketoesters-construction-fused01483nas a2200181 4500008004100000022001400041245012600055210006900181260000800250300001400258490000700272520079700279100002501076700002401101700002601125700002201151856012801173 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 uhttp://library.ncl.res.in/content/ready-access-565-trioxa-spiro-and-fused-ketals-ag-catalyzed-cascade-annulation-4-pentyn-101347nas a2200229 4500008004100000022001400041245010900055210006900164260000900233300001100242490000800253520055300261653002500814653001800839653002100857653002100878653002000899100002300919700002500942700002200967856012800989 2025 eng d a0040-403900aThe first enantioselective total synthesis of the eremophilane-type sesquiterpenoid (-)-peniroqueforin C0 afirst enantioselective total synthesis of the eremophilanetype s cJAN  a1553860 v1543 a

Herein, we report the first stereoselective total synthesis of the eremophilane-type sesquiterpenoid (-)-peniroqueforin C using a chiral-pool strategy. This synthetic route features the use of readily available (S)-(+)-carvone as a chiral building block, Robinson annulation to construct the decalin system, substrate-controlled stereoselective methylation, single-step annulative construction of a tricyclic gamma-ylidene-butenolide with concomitant alkene transposition, and direct lactone-to-lactam conversion as key transformations.

10aannulation reactions10aEremophilanes10aPeniroqueforin C10aSesquiterpenoids10aTotal synthesis1 aIngale, Sudhir, R.1 aVinodkumar, Ramavath1 aKontham, Ravindar uhttp://library.ncl.res.in/content/first-enantioselective-total-synthesis-eremophilane-type-sesquiterpenoid-peniroqueforin-c