Mansonone structure

Figure 5. Structures of mansonones from Hibiscus tiliaceus...

Gerber has isolated (+ )-epicubenol (81) from a Streptomyces species. This compound is the enantiomer of that found in the essential oil of Cedrela toona Roxb. The syntheses of four naturally-occurring phenolic sesquiterpenoids obtained from the essential oil of elm wood have been reported, viz. (82 R = Me), (82 R = CHO), (83 R = Me), and (83 R = CHO). The known o-quinone, mansonone C (84), has also been isolated from elm wood. The structure (85) of sesquichamaenol, a minor component of the essential oil of Chamaecyparis forrnosensis, has been deduced on the basis of spectroscopic evidence and synthesis. Piers et al. have published complete details of their syntheses of a- and ) -cubebenes (86). 

Baneijee et al.66 have developed an alternative synthesis of the compound (129) whose utility in synthesis of Mansonone F (120) has been reported by Suh and collaborators.65 This is described in Scheme 13. Tetralone (127) was reduced with sodium borohydride to alcohol which on alkylation with benzyl chloride produced benzyl derivative (132). Its conversion to (133) was attempted by treatment with boron tribromide in dichloromethane. C ompound (133) (characterized b y m ass s pectroscopy) was obtained in poor yield. The major product was the diol (134), whose structure was confirmed by spectral data. It indicates that the demethylation was accompanied by debenzylation. Treatment of diol (134) with triethyl orthoformate and aluminium chloride afforded aldehyde (135) which was subjected to catalytic hydrogenation to produce compound (136). It was transformed to ketone (137) by oxidation and then made to react with methylmagnesium bromide in ether. The resulting tertiary alcohol on heating with p-toluenesulfonic acid in toluene for 24 hr produced the naphthalene (129) in 78% yield. 

One of the early examples of an intramolecular Diels-Alder reaction of benzynes involved cycloaddition to a furan that was tethered to the benzyne moiety . Diazoti-zation of anthranilic acid 669 gave in 86% yield the cycloadduct 670, which was subsequently converted to the o-naphthoquinone 671 (mansonone E 7 steps) as well as to the structurally related mansonones F and I and biflorin. ... 

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