title: 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.
authors.affiliation: School of Chemistry, University of Nottingham, University Park, Nottingham, UK NG7 2RD.
authors.forename: Jalindar
authors.initials: J
authors.lastname: Padwal
authors.forename: William
authors.initials: W
authors.lastname: Lewis
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Moody
mesh_terms: D029788:Diospyros / Q000737:chemistry*; D011564:Furocoumarins / Q000737:chemistry*; D006576:Heterocyclic Compounds, 4 or More Rings / Q000737:chemistry*; D007536:Isomerism; D008958:Models, Molecular; D015394:Molecular Structure; D009285:Naphthoquinones / Q000737:chemistry*; D011809:Quinones / Q000138:chemical synthesis* / Q000302:isolation & purification
chemical_list: D011564:Furocoumarins; D006576:Heterocyclic Compounds, 4 or More Rings; D009285:Naphthoquinones; D011809:Quinones; C560348:crassiflorone