Neighboring Group Participation by Chromium in Substitution Reactions of (η<sup>6</sup>-Arene)tricarbonylchromium Complexes

and, Craig A. Merlic; Miller, Michael M.

doi:10.1021/om000980w

Cited by 23 publications

(16 citation statements)

References 39 publications

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“…The mixture was then filtered, and the solvent was removed in vacuo . The residue was purified by preparative silica gel TLC with PE/EA (3:1) as the eluent to give the corresponding products (46.7 mg, 86% yield) …”

Section: Methodsmentioning

confidence: 99%

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Synthesis of 9,9-Disubstituted Fluorenes from 2-Iodobiphenyls and α-Diazoesters under Palladium Catalysis

Shi

et al. 2018

J. Org. Chem.

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Section: Methodsmentioning

confidence: 99%

“…The ester groups of the disubstituted fluorenes can be reduced to hydroxyl groups (Scheme ). The resulting hydroxyl groups allow the fluorenes to be further derivatized, which extends the synthetic applications of the fluorene products.…”

mentioning

confidence: 99%

Synthesis of 9,9-Disubstituted Fluorenes from 2-Iodobiphenyls and α-Diazoesters under Palladium Catalysis

Shi

et al. 2018

J. Org. Chem.

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“…Further attempts using oxidative radical cyclization conditions did not lead to a significant improvement. Ultimately, the optimal conditions for the synthesis of tricyclic ketone 19 were found to involve an intramolecular C2-alkylation of the pyrrole nucleus by activation of the primary iodide 18 . Under strictly anhydrous conditions, treatment of ( R )- 18 with silver tetrafluoroborate in a dichloromethane−benzene (3:1) solvent mixture at ambient temperature furnished the tricyclic ketone ( R )- 19 in 75% yield (Scheme ).…”

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confidence: 99%

Enantioselective Total Synthesis of Tricyclic Myrmicarin Alkaloids

Movassaghi

Ondrus

2005

Org. Lett.

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An enantioselective gram-scale synthesis of a key dihydroindolizine intermediate for the preparation of myrmicarin alkaloids is described. Key transformations in this convergent approach include a stereospecific palladium-catalyzed N-vinylation of a pyrrole with a vinyl triflate, a copper-catalyzed enantioselective conjugate reduction of a β-pyrrolyl enoate, and a regioselective Friedel-Crafts reaction. The synthesis of optically active and isomerically pure samples of (4aR)-myrmicarins 215A, 215B, and 217 in addition to their respective C4a-epimers is presented. The myrmicarins are a family of structurally fascinating alkaloids isolated from the poison gland secretions of the African ant species Myrmicaria opaciventris (Figure 1). 1 Despite significant isolation and purification challenges due to air and temperature sensitivity, elegant spectroscopic studies have revealed their molecular structures. 2 The pyrroloindolizine core of myrmicarins 215A (1), 215B (2), and 217 (3) is a common structural motif within many of these alkaloids. Within the family, only the absolute stereochemistry of myrmicarin 237A (4) has been secured through an enantioselective synthesis. 1a,3 Interestingly, the conversion of an unsaturated derivative of 4 to myrmicarin 217 (3) suggests the possible biogenesis of other myrmicarins from simpler indolizine derivatives. 1b,4 The synthesis of (R)-myrmicarin 217 (3) and (R)-myrmicarin 215 as a mixture of olefin isomers has been reported starting with D-glutamic acid. 5 The intriguing molecular structures of these poisonous alkaloids combined with challenges associated with their sensitivity provide an exciting arena to test and discover new methodologies for organic synthesis. Herein we describe a convergent synthesis of all naturally occurring tricyclic myrmicarin alkaloids employing an efficient approach to a pivotal optically active dihydroindolizine intermediate. The first preparation of isomerically pure samples of myrmicarins 215A and 215B is discussed. Key steps of the synthesis include an efficient palladium-catalyzed fragment coupling reaction, a copper catalyzed asymmetric conjugate reduction and a regioselective Friedel-Crafts reaction. We envisioned utilization of the optically active dihydroindolizine 7 as a key intermediate for the preparation of myrmicarin alkaloids (Scheme 1). A regioselective Friedel-Crafts reaction of the pyrrole ring (C7a-alkylation) upon Brönsted-acid activation of the dimethoxyacetal 8 and elimination of methanol was expected to afford the bicyclic vinyl pyrrole 7. We planned to use a metal-catalyzed enantioselective conjugate reduction of the β-pyrrolyl enoate 9 to introduce the C4a-stereochemistry. 6,7 A convergent synthesis of the pyrrolylenoate 9 was envisioned via a metal-catalyzed union of pyrrole 11 and readily available Z-vinyl triflate 10 (Scheme 1). The synthesis of the required β-pyrrolylenoate 9 began with the Claisen condensation of the lithium enolate 12 and methyl 4-(dimethoxy)-butyrate (13) 8 to give the β-ketoester 14 (Scheme 2). The lit...

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“…The crystal structure determinations have been carried out for the iodopropylbenzene and pyrrolylpropylbenzene species. 37 The arene exchange reaction of [(η 6 -C 6 H 5 F)-Cr(CO) 2 L] (L = di(pyrrolyl){(2-methylthio)pyrrolyl}phosphine) with benzene-d 6 to give [(η 6 -C 6 D 6 )Cr(CO) 2 L] was studied in order to gain insight into accelerated arene ligand exchange in [(η 6 -arene)Cr(CO) 3 ] complexes. 38 Treatment of [(η 39 The ionisation of planar chiral ortho-substituted (arene)Cr(CO) 3 -substituted α-propargylic acetates with Lewis acids has given stable (arene)Cr(CO) 3 -substituted α-propargyl cations.…”

Section: Organometallics and Carbon-donor Ligandsmentioning

confidence: 99%

12 Chromium, molybdenum and tungsten

Malito¹

2002

Annu. Rep. Prog. Chem., Sect. A: Inorg. Chem.

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Neighboring Group Participation by Chromium in Substitution Reactions of (η⁶-Arene)tricarbonylchromium Complexes

Abstract: η 6 -Arene)tricarbonylchromium complexes with leaving groups at the β-or γ-positions undergo nucleophilic substitution reactions with net retention of stereochemistry via neighboring group participation from the coordinatively saturated chromium atom.

Cited by 23 publications

References 39 publications

Synthesis of 9,9-Disubstituted Fluorenes from 2-Iodobiphenyls and α-Diazoesters under Palladium Catalysis

Synthesis of 9,9-Disubstituted Fluorenes from 2-Iodobiphenyls and α-Diazoesters under Palladium Catalysis

Enantioselective Total Synthesis of Tricyclic Myrmicarin Alkaloids

12 Chromium, molybdenum and tungsten

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Neighboring Group Participation by Chromium in Substitution Reactions of (η6-Arene)tricarbonylchromium Complexes

Abstract: η 6 -Arene)tricarbonylchromium complexes with leaving groups at the β-or γ-positions undergo nucleophilic substitution reactions with net retention of stereochemistry via neighboring group participation from the coordinatively saturated chromium atom.

Cited by 23 publications

References 39 publications

Synthesis of 9,9-Disubstituted Fluorenes from 2-Iodobiphenyls and α-Diazoesters under Palladium Catalysis

Synthesis of 9,9-Disubstituted Fluorenes from 2-Iodobiphenyls and α-Diazoesters under Palladium Catalysis

Enantioselective Total Synthesis of Tricyclic Myrmicarin Alkaloids

12 Chromium, molybdenum and tungsten

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Neighboring Group Participation by Chromium in Substitution Reactions of (η⁶-Arene)tricarbonylchromium Complexes