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Padwa A, Cochran JE, Kappe CO. Tandem Pummerer-Diels-Alder Reaction Sequence. A Novel Cascade Process for the Preparation of 1-Arylnaphthalene Lignans. J Org Chem. 1996;61(11):3706-3714doi: 10.1021/jo960295s.
Padwa, A., Cochran, J. E., & Kappe, C. O. (1996). Tandem Pummerer-Diels-Alder Reaction Sequence. A Novel Cascade Process for the Preparation of 1-Arylnaphthalene Lignans. The Journal of organic chemistry, 61(11), 3706-3714. https://doi.org/10.1021/jo960295s
Padwa, Albert, et al. "Tandem Pummerer-Diels-Alder Reaction Sequence. A Novel Cascade Process for the Preparation of 1-Arylnaphthalene Lignans." The Journal of organic chemistry vol. 61,11 (1996): 3706-3714. doi: https://doi.org/10.1021/jo960295s
Padwa A, Cochran JE, Kappe CO. Tandem Pummerer-Diels-Alder Reaction Sequence. A Novel Cascade Process for the Preparation of 1-Arylnaphthalene Lignans. J Org Chem. 1996 May 31;61(11):3706-3714. doi: 10.1021/jo960295s. PMID: 11667219.
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J Org Chem. 1996 May 31;61(11):3706-3714. doi: 10.1021/jo960295s.

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

The Journal of organic chemistry

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

Affiliations

  1. Department of Chemistry, Emory University, Atlanta, Georgia 30322.

PMID: 11667219 DOI: 10.1021/jo960295s

Abstract

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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