Generation and Subsequent Cycloaddition Chemistry of α-Amino Isobenzofurans Formed by Cationic Cyclization

Kappe, C. Oliver; Cochran, John E.; Padwa, Albert

doi:10.1016/0040-4039(95)02013-f

Cited by 21 publications

(34 citation statements)

References 21 publications

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“…There are only a few cases in the literature where Diels−Alder cycloadditions of 2-aminofurans have been described. − The paucity of examples is undoubtedly due to the inaccessibility and inherent instability of the 2-aminofuran ring system. − Recently, we reported on the Pummerer-induced cyclization of keto sulfoxides as a method to prepare thio-substituted isobenzofurans of type 8 . The α-thiocarbocation generated from the Pummerer reaction of an o- benzoyl-substituted sulfoxide ( 7a ) was intercepted by the adjacent keto group to produce isobenzofuran 8 as a transient intermediate which undergoes a subsequent Diels−Alder cycloaddition with an added dienophile.…”

Section: Resultsmentioning

confidence: 99%

A Triple Cascade Sequence as a Strategy for the Construction of the Erythrinane Skeleton

et al. 1998

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α-Thiocarbocations generated from Pummerer reactions of several o-imido sulfoxides were intercepted by adjacent carbonyl groups to produce α-amido-substituted isobenzofurans as transient intermediates. When an olefinic tether was present, intramolecular Diels−Alder cycloaddition occurred followed by a ring-opening−elimination sequence that produced an N-acyliminium ion. Deprotonation of the iminium ion led to oxindole derivatives in good yields. When the iminium ion contained both a blocking substituent, such as a carbomethoxy group, as well as an activated aromatic π-tether, the N-acyliminium ion intermediate underwent stereoselective spirocyclization to afford cis-3,4-benzoerythrinane or homoerythrinane derivatives in good yield. The overall triple cascade sequence represents an efficient one-pot approach toward the erythrina skeleton in which the spirocyclic ABC skeleton is assembled in a single operation. The scope and limitations of the triple cascade were explored by varying both the olefinic and nucleophilic tethers. The required sulfoxide precursors for these Pummerer-induced transformations were easily synthesized starting from 2-[(ethylthio)methyl]benzoic acid. The tandem Pummerer/Diels−Alder/N-acyliminium ion cyclization was used for the synthesis of indoloisoquinoline 38. Since compound 38 was converted to 47 which, in turn, was transformed into erysotramidine (2), its preparation represents an extraordinarily facile, formal synthesis of this member of the Erythrina alkaloid family.

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Section: Resultsmentioning

confidence: 99%

A Triple Cascade Sequence as a Strategy for the Construction of the Erythrinane Skeleton

et al. 1998

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“…This method is particularly useful since carboxylic acid 15 can be prepared in large quantities and can serve as an intermediate for the preparation of other acid analogs ( i.e. amides, esters) which we have employed in related Pummerer-based transformations . Finally, the oxidation of sulfides 11 and 17 to the desired sulfoxides 18 and 19 was carried out in very high yield using NaIO 4 as the oxidizing reagent .…”

Section: Resultsmentioning

confidence: 99%

Tandem Pummerer−Diels−Alder Reaction Sequence. A Novel Cascade Process for the Preparation of 1-Arylnaphthalene Lignans

Padwa

Kappe

1996

J. Org. Chem.

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The alpha-thiocarbocation generated from the Pummerer reaction of an o-benzoyl-substituted sulfoxide is intercepted by the adjacent keto group to produce an alpha-thio isobenzofuran as a transient intermediate which undergoes a subsequent Diels-Alder cycloaddition with added dienophiles. Acid-catalyzed ring-opening of the cycloadduct followed by aromatization gave an arylnaphthalene derivative. With acetylenic dienophiles, the tandem cyclization-cycloaddition sequence provided tetralones which result from a pinacol-type rearrangement of the primary cycloadducts. The versatility of the approach is highlighted through the synthesis of taiwanin C and E and justicidin E. The alpha-thiocarbocation generated from the Pummerer reaction of benzo[1,3]dioxol-5-yl-[6-[(ethylsulfinyl)methyl]benzo[1,3]dioxol-5-yl)methanone is intercepted by the adjacent keto group to produce an alpha-thioisobenzofuran as a transient intermediate which undergoes a subsequent Diels-Alder cycloaddition with dimethyl maleate. The initially formed Diels-Alder cycloadduct was readily converted to 5-benzo[1,3]dioxol-5-yl-8-(ethylthio)naphtho[2,3-d][1,3]dioxole-6,7-dicarboxylic acid dimethyl ester by loss of water on treatment with p-toluenesulfonic acid. Desulfurization of the thionaphthalene with Ra/Ni followed by hydrolysis of the less hindered methyl ester afforded 5-benzo[1,3]dioxol-5-ylnaphtho[2,3-d][1,3]dioxole-6,7-dicarboxylic acid 6-methyl ester which was further transformed into taiwanin C and justicidin E in good yield. Oxidation of the initial Diels-Alder cycloadduct with NaIO(4) in the presence of RuCl(3) followed by extrusion of ethyl sulfinate gave a naphthol derivative which can be converted into taiwanin E.

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“…The resulting anionic aza- ortho -quinodimethane intermediate 14 then, by [1,5]-hydrogen shift gives the ortho -benzylaniline-derived Schiff base 15 , which undergoes cyclization to give the indoline derivative 16 , and this by subsequent elimination of SO 2 and protonation yields 17 . The latter, like many indolines [ 46 – 48 ] probably is susceptible to very rapid oxidation upon work-up in air to give the corresponding indole 18 .…”

Section: Resultsmentioning

confidence: 99%

Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides

Rassadin¹,

Scholz²,

Klochkova³

et al. 2017

Beilstein J. Org. Chem.

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Generation and Subsequent Cycloaddition Chemistry of α-Amino Isobenzofurans Formed by Cationic Cyclization

Cited by 21 publications

References 21 publications

A Triple Cascade Sequence as a Strategy for the Construction of the Erythrinane Skeleton

A Triple Cascade Sequence as a Strategy for the Construction of the Erythrinane Skeleton

Tandem Pummerer−Diels−Alder Reaction Sequence. A Novel Cascade Process for the Preparation of 1-Arylnaphthalene Lignans

Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides

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