An alternative synthesis of (.+-.)-.alpha.- and (.+-.)-.gamma.-lycoranes

Umezawa, Bunsuke; Hoshino, Osamu; Sawaki, Shohei; Sato, Seiichi; Numao, Naganori

doi:10.1021/jo00862a025

Cited by 29 publications

(5 citation statements)

References 3 publications

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“…Subsequently, debenzylation and olefin hydrogenation under atmospheric H 2 on Pd/C generated the known octahydroindole 11 , which exhibited spectral properties in agreement with the known material . Finally, we carried out the Pictet‐Spengler ring closure of 11 by following the Umezawa's conditions to afford (±)‐γ‐lycorane …”

Section: Methodsmentioning

confidence: 92%

Tandem [1,2]‐Wittig Rearrangement/Lactonization of γ‐Benzyloxy Vinylogous Urethanes: Application to the Synthetic Studies of Maculalactone A, Planchol C and γ‐Lycorane

2017

Asian J Org Chem

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At andem [1,2]-Wittig rearrangement/lactonization of g-benzyloxy vinylogousu rethanes is presented herein. The resulting butenolides featuring various benzyl substituents at the g-position are structurally diverse compounds found in natural products. The usefulness of this synthetic approach was demonstrated in the formal synthesis of maculalactone A, rapid assemblyo ft he tricyclic core of planchol C, and the total synthesis of g-lycorane.The rearrangemento fa-alkoxyc arbanions is one of the important reaction for CÀCb ondf orming methods. In particular,t he [2,3]-Wittig rearrangement,w hich allow the transformationo f an allylic ether into ah omoallylic alcohol, has been highly developedi nv arious fields of organic synthesis.[1] By contrast, the [1,2]-Wittig rearrangement has received less attention [2] and has rarely been applied in the synthesis of naturalp roducts [3] and pharmaceuticals.[2s] This lack of popularity has mainly resulted from the preparation of a-etherealc arbanions, which relies heavily on the use of the benzyl group as ac arbanionstabilizing group in the anion formation step (Scheme 1a). However,t he stability and synthetic potentialo ft he phenyl ring limits the synthetic applications of this approach. [1,2]-shifts of electron-withdrawing group (EWG)-bearing ethers involvingt he formation of new stereocenters are scarce, because EWGs stabilizing the a-ethereal carbanions can sometimesu ndergo eliminationr eactions to form carbonyl compounds (Scheme 1b).[4] To date, only af ew examples have been reported that allow accesst ot he corresponding carbinols in the presenceo fE WGs, such as ketones, [5] acetamides, [6] and b-lactams (Scheme 1c).[7] Recently,s ignificant progress has been made using an asymmetric tandem [1,2]-Wittig/Aldol or [1,2]-Wittig/Mannich reactions of glycolate esters, which provide a,b-dihydroxy esters and a-hydroxy b-amino esters in high stereoselectivities, respectively. [3b, 8] These tandem approaches not only strikingly complement traditional carbanion-stabilizing groups but also allow ac ascade sequence to efficiently forge complex chemical structures.Inspired by our previouss tudies on the asymmetric aldol reaction of g-benzyloxy vinylogousu rethanew ith aldehydes, under certain circumstances, aminute amount of g-benzyl substitutedv inylogous urethane lactone was obtained (Scheme 2a). [9] We envisioned that the rearrangement of av inylogous urethane system possessing an EWG-bearing moiety and ab enzyloxy-migrating terminus might undergo at andem [a] Dr

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Section: Methodsmentioning

confidence: 92%

Tandem [1,2]‐Wittig Rearrangement/Lactonization of γ‐Benzyloxy Vinylogous Urethanes: Application to the Synthetic Studies of Maculalactone A, Planchol C and γ‐Lycorane

2017

Asian J Org Chem

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“…Umezawa et al [166] reported the synthesis of both (�)-αlycorane and (�)-γ-lycorane using ketoacid 361. Alkene 357 was synthesized in 2 steps by addition of Grignard reagent 218 to cyclohexanone 136 followed by HCl treatment produced the adduct in 88 % yield.…”

Section: Miscellaneousmentioning

confidence: 99%

“…Umezawa et al [166] . reported the synthesis of both (±)‐α‐lycorane and (±)‐γ‐lycorane using ketoacid 361 .…”

Section: Miscellaneousmentioning

confidence: 99%

Synthetic Approaches to α‐, β‐, γ‐, and δ‐Lycoranes

et al. 2023

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Lycorane is a pentacyclic core presented in alkaloids isolated from the Amaryllidaceae family of herbaceous flowering plants. Members of this class of natural products have shown to display important biological properties including analgesic, antiviral, and antiproliferative activities. This review presents the known synthetic routes toward α‐, β‐, γ‐, and δ‐lycoranes. α‐(19 routes), β‐(10 routes), γ‐(38 routes), and δ‐(6 routes).

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“…4 Other synthetic methods employing enamines, 5 aryl-bismuth reagents, 6 silyl enol ethers, 7 1-nitrocycloalkenes, 8 electrochemical 9 and ring resizing 10 reactions have also been described. The most straightforward method involves palladium-catalyzed coupling of aryl halides with appropriate ketones.…”

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confidence: 99%

“…a The main product was 2-(4-methoxy-1-naphthyl)cyclopent-2-en-1-one (4m, 21% yield). 4 Cl solution (100 mL). The organic layer was separated and after removal of the solvent, formic acid (85%, 200 mL) was added to the crude alcohol.…”

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confidence: 99%

A Convenient Synthesis of 2-Naphthylcyclopentanones and 2-Naphthylcyclohexanones from 1-Naphthylcycloalkenes

Góra¹,

Luczynski²,

Sepioł³

2005

Synthesis

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The oxidation of naphthylcycloalkenes with hydrogen peroxide or MCPBA followed by acid catalyzed rearrangement of diol (epoxide), afforded a series of naphthylcycloalkanones in a very simple manner. The conditions allow preparation of naphthylcycloalkanones on a multigram scale.A number of methods have been reported for the synthesis of 2-arylcycloalkanones including: reaction of arylmagnesium halides or aryllithiums with chlorocycloalkanones, 1 diol and epoxide rearrangements, 2 radical ketone arylation, 3 and oxidation of arylcycloalkanols. 4 Other synthetic methods employing enamines, 5 aryl-bismuth reagents, 6 silyl enol ethers, 7 1-nitrocycloalkenes, 8 electrochemical 9 and ring resizing 10 reactions have also been described. The most straightforward method involves palladium-catalyzed coupling of aryl halides with appropriate ketones. 11Recently, we reported a new aromatic rearrangement leading to cycloalkaphenanthrenes having significant biological activity. 12 Efficient synthesis of these polycyclic aromatic hydrocarbons (PAHs) for investigations of the mechanism of PAH related carcinogenesis still remains a challenging problem. We needed a few grams each of the 2-naphthylcycloalkanones with varied substitutions in the aryl rings. Surprisingly, reports on easily applicable synthesis of naphthyl-and substituted naphthylcycloalkanones are rare. Among them, the approach involving oxidation of appropriate cycloalkene to the epoxide, followed by its acid-catalyzed rearrangement seemed to be the most promising. This method is operationally simple and the required starting materials are readily available via classical Grignard reaction. In this paper, we describe a multigram scale procedure for the preparation of the various substituted naphthylcycloalkanones.Our synthetic plan was similar to that reported for several simple phenyl derivatives, 2 but the experimental conditions were different due to higher reactivity of naphthalene rings.In all cases naphthylcycloalkenes were obtained by a twostep procedure involving Grignard reaction of appropriate naphthylmagnesium bromides with cycloalkanones and dehydration of crude alcohols 2a-l by heating with formic acid (Scheme 1). Conversion of 1 to the intermediate alcohols 2 was carried out in diethyl ether or THF, depending on the solubility of 1. Yields and methods of isolation naphthylcycloalkenes 3 are described in Table 1. Scheme 1 i) Mg/Et 2 O (THF); ii) cyclopentanone or cyclohexanone; iii) 85% aq HCO 2 H, 100°CInitially we focused on hydrogen peroxide/formic acid as the oxidizing agent. First, 1-cyclopent-1-en-1-ylnaphthalene (3a) was chosen as a model for oxidation. After several trials we found that the best results were achieved when the H 2 O 2 /HCO 2 H mixture was added dropwise to a well-stirred solution of 1 in acetone. We have applied these conditions for converting different unsubstituted naphthylcycloakenes to the corresponding ketones 4. However, for most of the substituted naphthylcycloalkenes this oxidation procedure gave only 10-20% yield of the ...

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An alternative synthesis of (.+-.)-.alpha.- and (.+-.)-.gamma.-lycoranes

Cited by 29 publications

References 3 publications

Tandem [1,2]‐Wittig Rearrangement/Lactonization of γ‐Benzyloxy Vinylogous Urethanes: Application to the Synthetic Studies of Maculalactone A, Planchol C and γ‐Lycorane

Tandem [1,2]‐Wittig Rearrangement/Lactonization of γ‐Benzyloxy Vinylogous Urethanes: Application to the Synthetic Studies of Maculalactone A, Planchol C and γ‐Lycorane

Synthetic Approaches to α‐, β‐, γ‐, and δ‐Lycoranes

A Convenient Synthesis of 2-Naphthylcyclopentanones and 2-Naphthylcyclohexanones from 1-Naphthylcycloalkenes

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