Endoperoxides of naphthalenes. Synthesis and reactions of substituted 2,3-epoxynaphthalene 1,4-endoperoxides

Sasaoka, Michio; Hart, Harold

doi:10.1021/jo01317a013

Cited by 13 publications

(1 citation statement)

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“…Epoxidation with m-chloroperoxybenzoic acid dichloromethane afforded a single diastereomer syn-7 as shown by the NM product. This is in accordance to literature-known epoxidations of simple EPOs [51] and can be explained by steric interactions and hydrogen bondi oxide bridge. The epoxide syn-7 was isolated by column chromatography in analytically pure form (Scheme 3).…”

Section: Methodssupporting

confidence: 93%

Stereoselective [4+2] Cycloaddition of Singlet Oxygen to Naphthalenes Controlled by Carbohydrates

2021

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Stereoselective reactions of singlet oxygen are of current interest. Since enantioselective photooxygenations have not been realized efficiently, auxiliary control is an attractive alternative. However, the obtained peroxides are often too labile for isolation or further transformations into enantiomerically pure products. Herein, we describe the oxidation of naphthalenes by singlet oxygen, where the face selectivity is controlled by carbohydrates for the first time. The synthesis of the precursors is easily achieved starting from naphthoquinone and a protected glucose derivative in only two steps. Photooxygenations proceed smoothly at low temperature, and we detected the corresponding endoperoxides as sole products by NMR. They are labile and can thermally react back to the parent naphthalenes and singlet oxygen. However, we could isolate and characterize two enantiomerically pure peroxides, which are sufficiently stable at room temperature. An interesting influence of substituents on the stereoselectivities of the photooxygenations has been found, ranging from 51:49 to up to 91:9 dr (diastereomeric ratio). We explain this by a hindered rotation of the carbohydrate substituents, substantiated by a combination of NOESY measurements and theoretical calculations. Finally, we could transfer the chiral information from a pure endoperoxide to an epoxide, which was isolated after cleavage of the sugar chiral auxiliary in enantiomerically pure form.

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Section: Methodssupporting

confidence: 93%