Synthesis and oxidative fragmentation of catharanthine analogs. Comparison to the fragmentation — Coupling of catharanthine and vindoline

Sundberg, Richard J.; Hong, Jian; Smith, Stanton Q.; Sabat, Michal; Tabaković, Ibro

doi:10.1016/s0040-4020(98)00289-0

Cited by 64 publications

(51 citation statements)

References 44 publications

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“…The final stage, reduction of lactam 56, proved to be more difficult than expected, conventional reagents such as LiAlH 4 being completely ineffective. Fortunately, a protocol due to Sundberg and co-workers [31] using diborane generated in situ from NaBH 4 and BF 3 ¥ Et 2 O was successful and furnished crystalline (À)-ibogamine (22), identical with a sample of the natural alkaloid kindly provided by Professor Huffman of Clemson University.…”

Section: Tbsmentioning

confidence: 99%

Catalyzed Asymmetric DielsAlder Reactions of Benzoquinone. Total Synthesis of (−)‐Ibogamine

White

Choi

2002

Helvetica Chimica Acta

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Dedicated to Professor Dieter Seebach on the occasion of his 65th birthday and in recognition of his numerous contributions to asymmetric synthesis.The DielsÀAlder reaction of 1,4-benzoquinone with 1,3-dienes catalyzed by Mikami×s [Ti{(S)-binol(2 À)}Cl 2 ] complex (binol [1,1'-binaphthalene]-2,2'-diol) gives cycloadducts in good yield and in high enantiomer excess. A model is proposed to explain the observed absolute configuration of cycloadducts, and the reaction is used as the key step in an asymmetric synthesis leading to the alkaloid (À)-ibogamine.1. Introduction. ± The asymmetric DielsÀAlder reaction has become one of the most widely used constructs for the assembly of enantiomerically enriched chiral carbocycles [1]. In its catalyzed version, the reaction offers an especially powerful synthetic method, which can lead to adducts from achiral materials in good yield and high enantiomer excess (ee) at or below room temperature [2]. Most catalyzed cycloadditions have relied on two-point ligation of an achiral dienophile with the chiral catalyst to form a relatively rigid, highly asymmetric, activated complex [3]. Typical dienophiles in this class are b-dicarbonyl compounds, where chelation with a metal such as titanium bound to a chiral ligand creates a complex in which only one face of the dienophile is exposed for reaction with its diene partner. As a result, asymmetric DielsÀAlder additions in this mode can be very efficient. The asymmetric DielsÀAlder reaction with a dienophile such as a simple a,b-unsaturated ketone or a 1,4-quinone raises the question of whether stereocontrol can be exercised effectively by single-point ligation of a chiral catalyst with the lone pair of electrons of only one carbonyl group. This question was first answered in the affirmative by Mikami and co-workers who showed that the reaction of 1,4-naphthoquinone with 1-methoxybuta-1,3-diene in the presence of a [Ti IV {binol(2 À)}] catalyst (binol [1,1'-naphthalene]-2,2'-diol) led to diketone 1 in high ee (Scheme 1) [4]. Subsequently, we found that benzoquinone in the presence of the Mikami catalyst underwent DielsÀAlder cycloaddition with a 1,3-diene derivative in similarly high ee [5]. Other examples from the laboratories of Corey [6] and Nicolaou [7] illustrate the participation of substituted benzoquinones in asymmetric DielsÀAlder reactions catalyzed by Mikami×s [Ti{binol(2 À)}Cl 2 ] system, although the argument for single-point ligation in these cases is less clear. Recently, it was shown that a,b-unsaturated ketones, for which single-point ligation is obligatory, undergo DielsÀAlder addition to cyclopentadiene in the presence of a chiral imidazolidinone to give cycloadducts in moderate to high ee; however, the generality

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Section: Tbsmentioning

confidence: 99%

Catalyzed Asymmetric DielsAlder Reactions of Benzoquinone. Total Synthesis of (−)‐Ibogamine

White

Choi

2002

Helvetica Chimica Acta

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“…[14] Im Vergleich zu den Analoga ist bei Catharanthin die Indoleinheit in umgekehrter Anordnung an den Rest des Moleküls geknüpft (Schema 6). [15] Eines der wenigen Beispiele mit hoher Ausbeute bei der Witkop-Reaktion ist die Synthese von (AE)-Quebrachamin (41) durch Pagenkopf und Bajtos. [16] Auch hier wurden zuvor zwei andere Wege verfolgt, um die gewünschte C-C-Knüp-fung zu erreichen, bevor die Witkop-Cyclisierung zum Erfolg führte.…”

Section: Photocyclisierung Von 2-substituierten Indolenunclassified

Die Witkop‐Cyclisierung: eine photoinduzierte C‐H‐Aktivierung des Indolsystems

et al. 2013

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Untersuchungen von photochemisch induzierten Redoxprozessen leisten einen besonderen Beitrag zur organischen Photochemie und zu ihrer Anwendungen in der Synthese komplexer Zielstrukturen. Die richtige Wahl des Reduktions‐ und Oxidationspotentiale sowie die Energie des angeregten Zustands von Akzeptor und Donor müssen richtig gewählt werden, damit in diesem Redoxprozess über einen Einelektronentransfer ein intermediäres Radikalion erzeugt werden kann, das schließlich zu den Produkten weiterreagiert. Die Witkop‐Cyclisierung stellt eine intramolekulare Variante eines solchen Prozesses dar – typischerweise mit einem Indol‐Heterocyclus als Elektronendonor. Der synthetische Mehrwert dieser Reaktion besteht in einer C‐C‐Bindungsknüpfung ohne die sonst notwendige Präfunktionalisierung des Indolkerns. Dieser Kurzaufsatz behandelt bereits erfolgte Anwendungen der Reaktion und möchte zu ihrer Weiterentwicklung vor allem an komplexen Systemen anstoßen.

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“…In 1992 Sundberg and co-workers studied the modified Potier-Polonowski coupling reaction of catharnathine and vindoline, where they could firstly isolate and identify a highly reactive iminium (immonium, dihydropyridinium) intermediate at −20 • C using low-temperature NMR spectroscopy [70]. This key intermediate helped to optimize this reaction which was later used in many cases to produce VLB and VCR derivatives [71][72][73].…”

Section: Historical Examples Of Bisindole Structure Identification Bymentioning

confidence: 99%

Structure elucidation of indole–indoline type alkaloids: A retrospective account from the point of view of current NMR and MS technology

Béni¹,

Háda²,

Dubrovay³

et al. 2012

Journal of Pharmaceutical and Biomedical Analysis

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Synthesis and oxidative fragmentation of catharanthine analogs. Comparison to the fragmentation — Coupling of catharanthine and vindoline

Cited by 64 publications

References 44 publications

Catalyzed Asymmetric DielsAlder Reactions of Benzoquinone. Total Synthesis of (−)‐Ibogamine

Catalyzed Asymmetric DielsAlder Reactions of Benzoquinone. Total Synthesis of (−)‐Ibogamine

Die Witkop‐Cyclisierung: eine photoinduzierte C‐H‐Aktivierung des Indolsystems

Structure elucidation of indole–indoline type alkaloids: A retrospective account from the point of view of current NMR and MS technology

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