2015
DOI: 10.1039/c4ob02439g
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Construction of the tricyclic core of steenkrotin-type diterpenoids via intramolecular [3 + 2] cycloaddition

Abstract: A concise and diastereoselective route to the angularly fused [5-6-7] tricyclic carbon framework of the steenkrotin-type diterpenoids was reported. The key features of the strategy are based on an intramolecular nitrile oxide/alkene [3 + 2] cycloaddition and a regio-selective aldol/dehydration sequence.

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Cited by 12 publications
(29 citation statements)
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“…By detailed inspection of the structure, we conceived of preparing (AE)-steenkrotin A( 1)f rom [3,5,5,6,7] pentacyclic alkene 3 through as eries of late-stage functionalizations involvinga llylic oxidation at C3, bismethylation at C2 and C11, and epimerization at C7. The final cyclopentane ring of 3 could be accessed from [3,5,6,7] tetracycle 4 by an intramolecular alkylation [10] or aldol cyclization, [11] whichw ould also set the stereochemistry of the desired quaternary carbon at C9. The latter intermediate was envisioned to be obtained by elimination of alcohol 5.Aradical-initiated intramolecular Michael cyclization [12] of enone-aldehyde 6 was foreseen to install the requisite six-membered ring.…”
Section: Resultsmentioning
confidence: 99%
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“…By detailed inspection of the structure, we conceived of preparing (AE)-steenkrotin A( 1)f rom [3,5,5,6,7] pentacyclic alkene 3 through as eries of late-stage functionalizations involvinga llylic oxidation at C3, bismethylation at C2 and C11, and epimerization at C7. The final cyclopentane ring of 3 could be accessed from [3,5,6,7] tetracycle 4 by an intramolecular alkylation [10] or aldol cyclization, [11] whichw ould also set the stereochemistry of the desired quaternary carbon at C9. The latter intermediate was envisioned to be obtained by elimination of alcohol 5.Aradical-initiated intramolecular Michael cyclization [12] of enone-aldehyde 6 was foreseen to install the requisite six-membered ring.…”
Section: Resultsmentioning
confidence: 99%
“…[2] Recent efforts by Hussein and co-workers aimed at identifying novel diterpenoidsa sp otential medicinal leads resultedi nt he isolation of two new compounds with moderate antiplasmodial activities from the extract of leaves of C. Steenkampianus,w hich were named( + +)-steenkrotins Aa nd B (1 and 2,r espectively,Figure1). [3] The relative stereochemistry of (+ +)-steenkrotin A( 1)w as unambiguouslye stablished by X-ray diffraction analysis, revealing an intricate [3,5,5,6,7] structure containing at etracyclic carbon framework and as terically congested hydroxyl-tetrahydrofuran subunit. The highlyo xygenated (+ +)-steenkrotin B( 2)f eatures an unusual [5,6,6,7] tetracyclic skeleton containing an endoperoxide moiety.B oth molecules bear eight stereogenic centers, six of which are contiguous,including one all-carbon quaternary center.I nterestingly,e ven before its isolation,t he [3,5,6,7] tetracyclic structure of steenkrotin Aw as envisioned by Cha and co-workerst ob ef ormed throughapinacol-type rearrangement from an epoxy alcohol containing the tigliane skeleton.…”
Section: Introductionmentioning
confidence: 99%
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