Prenyl Dihydric Phenols

Reference has been made in the previous section to the isoiation (ref, 16) of the two isomeric Cg prenyiorcinols. Two of the tweive products from the reaction of orcinoi with 2-methyl-3-buten-2-oi in aqueous formic acid were shown to be the isomeric chromans, 2,2-dimethyi-5-hydroxy-7-methyichroman and 2,2-dimethyi- 

7-hydroxy-5-methyichroman. which were identicai with two compounds reported from the reaction of 3,3-dimethyiallyl diphenyl phosphate with orcinoi (ref. 28). The former was prepared from 3-methylbut-2-enol and diphenylphosphorochloridate. Upon heating with an excess of orcinoi at 120°C during several hours it gave diphenyl hydrogen phosphate and the two chromans 

As found (refs. 16,28), bis Cg prenyl derivatives of orcinoi can also give rise to isomeric tricyclic benzodipyrans such as the two compounds depicted. Certain of the remaining components of the reaction mixture could be isomeric mono O-prenyl C-prenyl compounds which in turn would be expected to afford 5- or 7-prenyl ethers of 2,2-dimethylchromans and the presence of C/0 triprenylorcinols and their transformation products might be anticipated. 

The products from the cyclisation of the two geranylorcinols in aqueous formic acid (ref. 16) have been studied and were found to consist of three chromans of the structure indicated. 

In addition two tricyclic hexahydroxanthenes (R = Me) resulted having the structures shown from spectroscopic evidence on related trans and c/s-fused 

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Probably because prenyl derivatives of dihydric phenols are more involved naturally and more reactive than those of the monhydric series as the precursors of many cyclic oxygen ring compounds they have attracted synthetic interest. Although the alkylation of hydroquinones affords good yields, the more reactive resorcinol series do not respond well and isomer formation occurs. Thus, (ref.9), hydroquinone as the disodium salt in hot benzene with 3-methylbuten-2-yl chloride gave 4-hydroxy-2-(3-methylbuten-2-yl)phenol in 66%... 

Although many of the complex natural chromene, chroman, pyran and benzofuran structures clearly have arisen from reactive prenyl precursors which themselves have invariably not been isolated, certain prenyl derivatives of dihydric phenols have served as model compounds in cyclisation processes likely to be the pathways towards those naturally occurring compounds. 2-Prenylphenols and 2- and 4-prenylresorcinols and orcinols with C5, C o, and... 

As examples of functionalised compounds aurogalaucin (ref.35) and flavoglaucin provide a link with synthetic monoprenyl dihydric phenols of the type discussed in 12.4. Although these two compounds (Table 12.1) do not appear to have been synthesised a study of their biosynthesis (ref. 36) illustrates a potential laboratory route through oxidation of 7-heptylsalicylic acid, synthesised by standard methods (ref. 83), by procedures such as Teuber oxidation with Fremy s salt followed by reduction, conversion of the methoxycarbonyl to the formyl group by hydride reduction and oxidation of the benzylic alcohol and finally prenylation, which would probably be non-specific. 

Synthesis of Prenyl Derivatives of Dihydric and Polyhydric Phenols... 

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