In a different strategy, 3-methoxysalicylaldehyde (VII) was protected as the silyl ether (VIII) using t-butyldimethylsilyl chloride and Et3N. Wittig reaction of aldehyde (VIII) with (9-hydroxynonyl)triphenylphosphonium bromide (IX) afforded olefin (X). This was alternatively prepared by addition of Grignard reagent (XI) to the aldehyde (VIII) to give carbinol (XII), which was further subjected to dehydration and acetal hydrolysis under acidic conditions to afford (X). Catalytic hydrogenation of olefin (X) furnished the 10-aryl decanol (XIII). The heptadecenyl side chain of (XVI) was then constructed by Swern oxidation of alcohol (XIII) to the corresponding aldehyde (XIV), followed by Wittig reaction with heptyltriphenylphosphonium bromide (XV). Desilylation of (XVI) with tetrabutylammonium fluoride gave the phenol precursor (VI), which was finally oxidized to the desired quinone by the same method as above.
Alternatively, the bis-methoxymethyl ether (XVIII), prepared from 2-bromo-6-methoxyhydroquinone (XVII), was subjected to palladium-catalyzed coupling with 9-decen-1-ol (XIX) to afford adduct (XX). After catalytic hydrogenation of olefin (XX), the resultant saturated alcohol (XXI) was oxidized to aldehyde (XXII) under Swern conditions. Wittig condensation of (XXII) with the phosphonium salt (XV) led to the heptadecenyl derivative (XXIII). Subsequent hydrolysis of the methoxymethyl ethers of (XXIII) by means of HBr in EtOH furnished the deprotected hydroquinone (XXIV). This was finally oxidized to the title quinone employing silver carbonate in benzene.
Irisquinone was originally isolated from some Iris species. The total synthesis of this compound has been reported by several procedures. 10-cis-Heptadecenoic acid (I) was converted to the Weinreb amide (II) via the corresponding acid chloride. Regiospecific ortho-lithiation of veratrole (III), followed by acylation with the N-methoxy amide (II), afforded ketone (IV). Selective mono-demethylation of (IV) with boron trichloride yielded phenol (V). Clemmensen reduction of the keto group of (V) employing zinc amalgam furnished 2-(cis-10-heptadecenyl)-6-methoxyphenol (VI). This was finally oxidized to the target quinone by means of oxygen gas in the presence of salcomine.