A Novel Synthesis of the Naturally Occurring Dibenzofurans Pannaric Acid and Schizopeltic Acid

Elix, JA; Parker, JL

doi:10.1071/ch9870187

Cited by 8 publications

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“…[4a,5] As this developed aryl migration is the retro-reaction of the reported Smiles rearrangement involving aryl migration from an ester to form an aryl ether. [6] And the Smiles rearrangement always requires ah eteroatom as the nucleophilic component and an electrophilic arene activated by strong electron-withdrawing groups,acarbonbased nucleophile,orfree-radical attack on the ipso-position of sulfonates or sulfonamides. [4] By taking advantage of visible-light photoredox catalysis,transition metals and astoichiometric amount of an oxidant and abase are avoided, thus leading to an environmentally benign and highly atom economical transformation.…”

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confidence: 99%

Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible‐Light Photoredox Catalysis

Wang

Cao

2017

Angewandte Chemie

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We have developed ahighly efficient aryl migration from an aryl ether to ac arboxylic acid group through retro-Smiles rearrangement by visible-light photoredoxc atalysis at ambient temperature.T ransition metals and as toichiometric oxidant and base are avoided in the transformation. Inspired by the high efficiency of this transformation and the fundamental importance of C À Ob ond cleavage,w ed eveloped anovel approachtothe C À Ocleavage of abiaryl ether to form two phenolic compounds,a sd emonstrated by ao ne-pot, twostep gram-scale reaction under mild conditions.T he aryl migration exhibits broad scope and can be applied to the synthesis of pharmaceutical compounds,s uch as guacetisal. Primary mechanistic studies indicate that the catalytic cycle occurs by ar eductive quenchingpathway.Various aryl-migration reactions have been developed and display broad application. [1] Notably,a ryl migration from an aryl ether to form an ester is rare.In1955, this migration was first observed upon the thermal decomposition of 2-phenoxybenzoyl peroxide in 25 %y ield by DeTar and Hlynsky. [2] Recently,t he migration was promoted by silver catalysis at 130 8 8CbyHossian and Jana, who used acarboxylic acid as the starting material. [3] However,t he stoichiometric strong oxidant K 2 S 2 O 8 and ab ase were required. Furthermore,t he transformation only resulted in up to 64 %y ield. No clear electronic effects on this aryl migration were observed. Thus, the transformation was identified as aSmiles rearrangement. Herein, we demonstrate ahighly efficient aryl migration from an aryl ether to form the ester of acarboxylic acid by visiblelight photoredox catalysis at ambient temperature without an oxidant [Scheme 1, Eq. (1)].O nly 1mol %o faphotosensitizer (PDI or Acr + -Mes ClO 4 À )a nd 10 mol %o fabase (K 2 HPO 4 )w ere required. Notably,e lectron-donating groups on the migrating aryl ring generally induced higher yields in this transformation, which differs from the typical Smiles rearrangement [4] and can be understood as ar etro-Smiles rearrangement. [4a,5] As this developed aryl migration is the retro-reaction of the reported Smiles rearrangement involving aryl migration from an ester to form an aryl ether. [6] And the Smiles rearrangement always requires ah eteroatom as the nucleophilic component and an electrophilic arene activated by strong electron-withdrawing groups,acarbonbased nucleophile,orfree-radical attack on the ipso-position of sulfonates or sulfonamides. [4] By taking advantage of visible-light photoredox catalysis,transition metals and astoichiometric amount of an oxidant and abase are avoided, thus leading to an environmentally benign and highly atom economical transformation. Moreover,i nspired by the high efficiency of this aryl migration and the fundamental importance of CÀOb ond cleavage, [4i, 7] we demonstrate an ovel approach to CÀOb ond cleavage in biaryl ethers to give two phenolic compounds in ao ne-pot, two-step reaction under mild conditions as as ubsequent transformation [Scheme 1, Eq. (2)].Visible...

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confidence: 99%

Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible‐Light Photoredox Catalysis

Wang

Cao

2017

Angewandte Chemie

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“…5 The Smiles rearrangement had been used previously on synthetic para depsides leading to a total synthesis of pannaric acid. 6 However, prior to our studies, the Smiles rearrangement had not been tested on naturally occurring para-depsides nor on depsides with an unprotected 4-hydroxy group.…”

Section: Resultsmentioning

confidence: 99%

“…The latter dibenzofuran 12, obtained in 12% overall yield from erythrin 1 in four steps, has been converted to pannaric acid 13. 6 Studies on the biological activity of lichen metabolites are scarce. Amongst the dibenzofurans, usnic acid has been extensively studied.…”

Section: Resultsmentioning

confidence: 99%

Novel Entry into 5-Decarboxydibenzofurans via Smiles Rearrangement of the Lichen Para-Depside, Erythrin

Thadhani

Choudhary

Andersen

et al. 2010

Journal of Chemical Research

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Erythrin, isolated in 7.3% yield from the lichen Roccella montagnei, was converted via a Smiles rearrangement to a series of diphenyl ethers. Those with a free carboxylic acid at C-1 underwent a novel decarboxylative oxidative cyclisation in the presence of Pd(OAc) 2 to produce 5-decarboxydibenzofurans. All compounds were assayed for their antioxidant and β-glucuronidase enzyme inhibitory activity.Lichens are symbiotic organisms of fungi (mycobionts) and algae (phycobionts) comprising about 18,000 species which have been recorded worldwide. 1 They accumulate large concentrations of secondary metabolites, comprising up to 20% of the thallus' dry weight. 2 The most characteristic of these are depsides, depsidones, diphenylethers and dibenzofurans. Depsides and to some extent depsidones are the major constituents. However, diphenyl ethers and dibenzofurans are rare. 3 Biosynthetically, depsides are considered to be the precursors of dibenzofurans through the intermediacy of diphenyl ethers. 4

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“…The compound 1a is isolated as a natural product for the first time, because previously it was only known as an intermediate in the biosynthesis of pannaric acid 2 formed by a phenol coupling between the position C6–C6′. Pannaric acid 2 and other depsides have been isolated from species in the lichen genera Psoroma , Lepraria and Leproloma (E lix and P arker 1987). To confirm the structure, the compound 1a was treated with a solution of diazomethane, and the dimethylester derivative 1b was obtained 2 .…”

Section: Resultsmentioning

confidence: 99%

A novel secondary metabolite from the Eucalyptus pathogen Mycosphaerella cryptica

et al. 2009

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The most abundant metabolite of the eucalyptus leaf spot pathogen Mycosphaerella cryptica was extracted from agar cultures. The structure of the compound was elucidated by detailed studies of NMR and MS data and by comparison with derivatives. The compound is a previously undescribed diphenylether structurally related to pannaric acid found in lichens. Culture extracts from another species of Mycosphaerella isolated from the same environment yielded 5-hydroxymethylfuran-3-carboxylic acid, a furan acidic compound previously isolated from a basidiomycete fungus. Assays for bioactivity of these metabolites revealed no evidence for antimicrobial activity. Some phytotoxicity was seen on newly emerged leaves of Eucalyptus globulus, but not on juvenile or adult leaves, when treated with either metabolite.

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A Novel Synthesis of the Naturally Occurring Dibenzofurans Pannaric Acid and Schizopeltic Acid

Cited by 8 publications

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Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible‐Light Photoredox Catalysis

Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible‐Light Photoredox Catalysis

Novel Entry into 5-Decarboxydibenzofurans via Smiles Rearrangement of the Lichen Para-Depside, Erythrin

A novel secondary metabolite from the Eucalyptus pathogen Mycosphaerella cryptica

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