An intramolecular Diels–Alder strategy to forskolin

Nicolaou, K. C.; Li, Wen Sen

doi:10.1039/c39850000421

Cited by 45 publications

(11 citation statements)

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“…Spater erkannten Kaiser und Lamparsky [5], dass in Wirklichkeit ein Gemisch entsteht aus einem stabilen Hauptprodukt, dem sie trans-Konfiguration zuschrieben, und einem in geringerer Menge gebildeten, labilen Epoxid, wel- Epimerisierung an C(6) via Enol. (6) und der Enon-Seitenkette. Das ist aber gleichbedeutend rnit einer partiellen Racemisierung des cis-Epoxids!…”

Section: Optisch Aktive 45-epoxy-45-dihydro-a -Ionone Undunclassified

“…Verseifung gab aus (+)-7 das Diol (+)-6, welches mit demjenigen, das aus (+)-(R)-a-Ionon ((+)-(R)-1) hergestellt worden war, bis auf geringe Unterschiede in den [a],-Werten identisch war, rnit ebenfalls positivem Cotton-Effekt bei 235 nm. Dies beweist die (R)-Chiralitat an C (6). Aus dem Ester (-)-7 entstand das Glycol (-)-6 rnit spiegelbildlicher CD-Kurve.…”

Section: Deln Welches Dann (-)-(6s)-8 Liefern Wiirde Aus (-)-(S)-a-unclassified

“…1st das Hauptprodukt der Epoxydierung von (+)-(R)-1 das cis-Epoxid (+)-4, so kommt dem labilen Nebenprodukt trans-Konfiguration ((+)-5) zu. Dessen Umwandlung in das stabile Diastereoisomere (+)-4 verlauft vermutlich iiber eine Enolisierung an C (6) und der Enon-Seitenkette. Das ist aber gleichbedeutend rnit einer partiellen Racemisierung des cis-Epoxids!…”

unclassified

“…Die Epoxydierung von a-Ionon mit Persauren ergibt also das stabile cis-Epoxid 4 als Haupt-und das labile trans-Epoxid 5 als Nebenprodukt. Die Angaben von [5] [6] Friihere ORD-Korrelationen [22]; Zusarnrnenstellung von CD-Messungen, [23-261. Anmerkung (20.2.1986): Soeben ist der erste Nachweis eines 4,5-Epoxycarotinoids in der Natur bekanntgeworden [31].…”

unclassified

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Optisch aktive 4,5‐Epoxy‐4,5‐dihydro‐α‐ionone und Synthese der stereoisomeren 4,5:4′,5′‐Diepoxy‐4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotine und der sterische Verlauf ihrer Hydrolyse

Uebelhart

Baumeler

Haag

et al. 1986

Helvetica Chimica Acta

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Optically Active 4,5‐Epoxy‐4,5‐dihydro‐α‐ionones; Synthesis of the Stereoisomeric 4,5:4′,5′‐Diepoxy‐4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotenes and the Steric Course of their Hydrolysis We prove that epoxidation with peracid of α‐ionone, contrary to a recently published statement, predominantly leads to the cis‐epoxide. Acid hydrolysis affords a single 4,5‐glycol whose structure, established by an X‐ray analysis, shows that oxirane opening occurred with inversion at the least substituted position (C(4)). Stable cis‐and trans‐epoxides are prepared by epoxidation of the C15‐phosphonates derived from α‐ionone. Both the racemic and optically active form are used for the synthesis of the 4,5:4′,5′‐diepoxy‐4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotenes having the following configuration in the end groups: meso‐cis/cis, meso‐trans/trans, rac‐cis/trans, rac‐ and (6R, 6′ R)‐cis/cis, rac‐ and (6R, 6′R)‐trans/trans, rac‐ and (6R, 6′R)‐cis/trans, and (6R, 6′ R)‐cis/ϵ. Acid hydrolysis of the cis/cis‐epoxycarotenoids under relatively strong conditions occurs again with inversion at C(4)/C(4′) in case of the cis/cis‐epoxycarotenoids, but at C(5)/C(5′) in case of the trans/trans‐epoxycarotenoids. An independent synthesis of this 4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotene‐4,5,4′,5′‐tetrol is presented. The irregular results of the oxirane hydrolysis are explained by assumption of neighbouring effects of the lateral chain. 400‐Mz‐1H‐NMR data are given for each of the stereoisomeric sets. In the visible range of the CD spectra, the (6R, 6R′)‐epoxycarotenoids compared with (6R, 6R′)‐ϵ,ϵ‐carotene exhibit an inversion of the Cotton effects.

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Section: Optisch Aktive 45-epoxy-45-dihydro-a -Ionone Undunclassified

Section: Deln Welches Dann (-)-(6s)-8 Liefern Wiirde Aus (-)-(S)-a-unclassified

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Optisch aktive 4,5‐Epoxy‐4,5‐dihydro‐α‐ionone und Synthese der stereoisomeren 4,5:4′,5′‐Diepoxy‐4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotine und der sterische Verlauf ihrer Hydrolyse

Uebelhart

Baumeler

Haag

et al. 1986

Helvetica Chimica Acta

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“…30 The known CBS reduction procedure was not feasible in our case because of poor reproducibility and the need for a large amount of expensive catalyst. 31,32 On the other hand, asymmetric hydrogenation using a ruthenium catalyst can be conducted easily on a preparative scale with a S/C ratio up to 500 and a substrate concentration as high as 2.5 M in 2-propanol.…”

Section: Construction Of the Arisugacin Skeletonmentioning

confidence: 91%

Absolute stereochemistries and total synthesis of (+)-arisugacins A and B, potent, orally bioactive and selective inhibitors of acetylcholinesterase

et al. 2004

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A Concise Stereoselective Route to the Pentacyclic Frameworks of Arisugacin A and Territrem B

et al. 2000

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An intramolecular Diels–Alder strategy to forskolin

Abstract: A strategy for the construction of the AB ring system of forskolin based on a novel intramolecular Diels-Alder reaction is reported.

Cited by 45 publications

References 1 publication

Optisch aktive 4,5‐Epoxy‐4,5‐dihydro‐α‐ionone und Synthese der stereoisomeren 4,5:4′,5′‐Diepoxy‐4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotine und der sterische Verlauf ihrer Hydrolyse

Optisch aktive 4,5‐Epoxy‐4,5‐dihydro‐α‐ionone und Synthese der stereoisomeren 4,5:4′,5′‐Diepoxy‐4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotine und der sterische Verlauf ihrer Hydrolyse

Absolute stereochemistries and total synthesis of (+)-arisugacins A and B, potent, orally bioactive and selective inhibitors of acetylcholinesterase

A Concise Stereoselective Route to the Pentacyclic Frameworks of Arisugacin A and Territrem B

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