Issue 9, 2011

Synthesis of the reported structure of crassiflorone, a naturally occurring quinone isolated from the African ebony Diospyros crassiflora, and regioisomeric pentacyclic furocoumarin naphthoquinones

Abstract

A synthesis of the structure reported for the natural product crassiflorone, a furocoumarin naphthoquinone, is described. The key steps are a Diels–Alder reaction to form 2-bromo-8-hydroxy-6-methylnaphthoquinone, followed by O-protection and copper(II) mediated coupling to 4-hydroxy-5-methylcoumarin to establish the pentacyclic framework whose structure was unambiguously confirmed by X-ray crystallography. Since the spectroscopic data of the synthetic material did not match those reported for the natural product, three further regioisomeric furocoumarin naphthoquinones were prepared by copper(II) mediated coupling of 4-hydroxy-5- or 8-methyl coumarins with 5-benzyloxy-2-bromo-7-methyl- or 8-benzyloxy-2-bromo-6-methyl-1,4-naphthoquinone. Again the spectroscopic data did not match those of the natural material and therefore the true structure of crassiflorone remains unknown.

Graphical abstract: Synthesis of the reported structure of crassiflorone, a naturally occurring quinone isolated from the African ebony Diospyros crassiflora, and regioisomeric pentacyclic furocoumarin naphthoquinones

Article information

Article type
Paper
Submitted
22 Dec 2010
Accepted
01 Feb 2011
First published
16 Mar 2011

Org. Biomol. Chem., 2011,9, 3484-3493

Synthesis of the reported structure of crassiflorone, a naturally occurring quinone isolated from the African ebony Diospyros crassiflora, and regioisomeric pentacyclic furocoumarin naphthoquinones

J. Padwal, W. Lewis and C. J. Moody, Org. Biomol. Chem., 2011, 9, 3484 DOI: 10.1039/C0OB01231A

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