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         Synthesis of 4-allyl-pyrocatechol (3,4-dihydroxy-allyl-benzene)
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4-allyl-pyrocatechol from Eugenol (by Startinout)

1mol Al turnings (or foil or powder all work well, powder is the quickest closely 
followed by foil then turnings a distant third) is combind with 1.5mol (note the 
excess of Al) of Iodine in 1000mL of cyclohexane (exchange solvent as needed but 
not ether!!!!!). This mix is stirred under reflux until the red colour has turned 
to a grey (about 1.5hrs with powder, 2-3 with foil, 4+ with turnngs). At this 
point the heat is turned off and the AlI3 in solvent allowed to cool to room 
tempeature with stirring. in a dropping funnel, eugenol (1mol), tetra n-butyl 
ammonium iodide(1/360 mol) and a little cyclohexane are combined. This is slowly 
dripped into the AlI3/cyclohexane with vigourous stirring and inert gas sheilding. 
After all the eugenol has been added the solutiuon is brought to reflux (it is a 
tan coloured slurry at this point, but upon refluxing turns less viscous) for 1 
hour. The solution is then cooled in an ice bath and hydrolysed with ~600mL of 
water, slowly.

The resultant mix is filtered under nitrogen and the solid collected immersed in 
ethyl acetate, this is swirled for a couple of minutes, then filtered. The ethyl 
aceate is seperated from the water (collected through the filtration) and removed 
and what you have left is a tan coloured solid with a charactistic 'smoke' smell 
and a melting point 45-51, althought this range could be tightened by 
recrystalisation or vac distillation with hot water in the condenser.

A few notes:

- If you are quick then maybe you can not bother with the inert atmoshpere in the 
  workup, however the filtering takes a long time (don't even consider using 
  gravity) beacause the Al is very finely divided and clogs up the filter paper.
- It seems the reactant ratios are critical so get them right.
- The workup is a shit for large quantities, any suggested impovements would be 
  appreciated. Note particularily that the next step (adding the methylene bridge) 
  requires the catechol to be dissolved in DMF, so we need to figure out a way to 
  end up with the 4-allyl catechol in DMF. Looking forward to your suggestions.

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       The Base Catalysed Rearrangement of Catechol Mono-allyl Ethers
                   J. Chem. Soc. Chem. Comm. 494 (1974)
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Summary: The base catalysed rearrangement of catechol mono-allyl ether at 78°C 
involves successive sigmatropic rearrangements to give products that differ from 
those obtained by sigmatropic rearrangements under normal Claisen conditions.

The thermal rearrangement of catechol mono-allyl ether (1) is reported [1] to give 
at 160-200°C a mixture of products, 3-allyl-catechol (3) and 4-allylcatechol (4), 
in the ratio 5:4, apparently resulting from competing ortho- and para-Claisen 
rearrangements [2]. Our investigation of this reaction shows that the ratio of the 
products, (3) and (4), and the rate of the rearrangement are sensitive to the 
pH at which the reaction is carried out. Thus in ethanolic HCl (2 drops HCl in 
25 ml EtOH) at 180°C the ratio of (3):(4) is 2:1 and in ethanol containing 
1 equiv. of NaOEt at 78°C the reaction proceeds at approximately the same rate 
and the ratio (3):(4) is 1:4. These preliminary observations suggested that the
rearrangement of (1) is base catalysed and that the rearrangement of the anion 
of (1) takes a different course from that of the un-ionised phenol.

References:
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[1] JCS 1663 (1927) and Chem. Abs. 61, 11919 (1964) and Ind. J. Chem. 2, 323 (1964)
[2] Quart. Rev. 22, 391 (1968) and Chem. Brit. 5, 108 (1969)


Rhodium:

The predominantly formed 4-allyl-catechol is readily converted into safrole by 
methylenation of the phenol groups with dichloromethane and K2CO3 in acetone. 

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3,4-dihydroxy-allyl-benzene:

mp: 46 ... 48.5°C, cryst. solvents: benzene / petroleum, ether, light petroleum
bp: 123 - 124 (1 torr), 
    123 - 125 (1 - 2 torr), 
    156 - 158 (16 torr), 
    155 - 157 (13 torr), 
    147 - 149 (10 torr), 
    141 - 144 (7 torr), 
     98 - 102 (5 torr),
          139 (4 torr), 
    120 - 123 (2 torr)

Solubility: 25 g/l in H2O at 26°C

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