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      Novel route to 3,4-dihydroxyallylbenzene (aka 4-allyl-pyrocatechol)
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Psychokitty:

The title of the article is "The Base Catalysed Rearrangement of Catechol
Mono-allyl Ethers" published in Journal of the Chemical Society, Chemical
Communications, 1974, p.494.

According to the article, if catechol mono-allyl ether is rearranged
"in ethanol containing one equivalent of NaOEt at 78 deg C" a 1:4 ratio
of 2,3-allylpyrocatechol to 3,4-allylpyrocatechol is the end product.

This is good news bees. Catechol mono-allyl ether is fucking easy and hell to
make from catechol and allylbromide (both commercially available). And both
sodium ethoxide and ethanol are just as readily available.

My only confusion is in regard to the vagueness about the volume of ethanol and
weight of sodium ethoxide to use. Are the ratios equal volumes and weights of
reagents 1:1:1 of catechol mono-allyl ether,ethanol, and NaOEt?

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Rhodium:

No, they are referring to 1:1 of NaOEt/allyl ether, and then use an excess of
refluxing absolute ethanol as the solvent for the rearrangement. I guess that
with the free phenol group completely deprotonated (by NaOEt) the benzene
molecule behaves differently to give predominately para allylpyrocatechol.

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Psychokitty:

Here's the synthesis of the intermediate pyrocatechol mono-allyl ether:

Taken from JACS vol. 52, 1930, pp.1700-1706
"The Behavior of Allyl Derivatives of Catechol and Resorcinol Toward Heat"

"Monoallyl Ether or Pyrocatechol:

Molar quantities of potassium carbonate and catechol were mixed in 200 mL of
acetone, with some evolution of heat. The flask containing this mixture was then
fitted with a stirrer and attached to a reflux condenser. A mole of allylbromide
(or one mole of allylchloride and NaI [I got this information from another
source]) was added slowly and with constant stirring. When about three-fourths
of it had been added, external cooling of the flask was necessary to prevent too
vigorous boiling. The remaining allylbromide was added with less evolution of
heat. Refluxing on a water bath with continual stirring was continued for four
hours. After cooling, the solid material was filtered off and washed with 50 mL
of acetone. The washing were added to the first filtrate and the acetone was
removed by distillation. A test portion of the residual oil was placed in a few
mL of sodium hydroxide solution. Since it seemed to dissolve completely, this
demonstrated the absence of any great amount of the diallyl ether. The oil was
then fractionally distilled and the portion coming over at 108-113 deg C @ 18
torr was collected; yield 70%."

The above proceedure originally used resorcinol as its experimental model. But
the figures for catechol and its monoallyl ether are correct as inticated in the
article's table.

Here's more information:

"General Method of Preparation of the Allyl Ethers:

In general, the catechol or resorcinol was refluxed (Note: This period of
refluxing was necessary for good yields even where there was a considerable heat
of reaction at the outset) for four to five hours in acetone solution with the
calculated quantity of allyl bromide and with a slight excess of fused potassium
carbonate. For convenience in working up the products, a minimum volume of
acetone was usually taken. Ordinarily the weight of the catechol or resorcinol
compound exceeded the weight of the solvent used. At the termination of the
reflux period the mixture was diluted with three or four times its weight of
water, the layer of oil which separated was removed, and the aqueous layer
thrice extracted... After drying over anhydrous sodium sulfate or potassium
carbonate, the ether was removed and the residual material fractionated in
vacuo...  Purification by vacuum distillation was frequently impossible because
of prior rearrangement. In such cases the rearranged product was purified
instead. The monoallyl ethers gave the characteristic color reactions with
ferric chloride solution. They yielded no precipitate with lead acetate solution
in acetone."

Don't know about that last part about rearrangement occurring during vacuum
distillation. The monoallyl ether of catechol DOES have a distillation temp at
reduced pressure and temperature. Maybe this is only in reference to the
monoallyl ether of resorcinol. Either way, I suppose the intermediate monoallyl
ether could be purified by first making the sodium phenolate in water, wash with
solvent and then reconstitue the monoallyl ether with the addition of some acid.
Who knows? What I am sure of is that the above proceedure is VERY easy to
perform and seems to be quite flexible. Perhaps PTCs could be used to effect
this reaction more quickly and in higher yield using the Williamson synthesis
instead.

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Psychokitty:

The reaction time and volume of solvent to use. My guess is that the both of
these factors would be critical to the success of the reaction as NaOEt is a
strong base and with continued excessive exposure to the formed
allylpyrocatechol, it could very well effect a double bond migration that would
confusingly provide the experimentor with a mixture of catechol propenyl
benzenes, the properies of which would be anyone's best guess.

Sooooooo, am I right in assuming that the article does NOT indeed indicate how
much solvent to use and nor even generally how long the reaction should go?

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Rhodium:

The amount of solvent is probably of little importance, as long as you use at
least 2-3 parts of it to one part ether. The first time the reaction is run you
can probably follow it with TLC to estimate the proper reaction time (unless
someone finds a better description in beilstein).

The NaOEt will react completely with the free phenol, forming ethanol and the
sodium phenolate salt. Neither is a strong enough base to mess with the allyl
chain.

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Psychokitty:
      
So are you then saying that "1:1 allyl ether/NaOEt" is in equimolar amounts or
in equal weights? 

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Rhodium:

Equimolar amounts of ether/NaOEt, and then 2-3 times the weight of the ether in
ANHYDROUS ethanol as solvent. Reflux for a few hours and then evaporate the
solvent, and take up the residue in 2M NaOH. Wash with DCM, acidify and extract
with DCM. Evaporate the solvent and distill off the allyl-catechols.

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Psychokitty:
          
Here's another synthesis for the intermediate mono-allyl ether of pyrocatechol 
and the final allylpyrocatechol:

Taken from CA vol. 61 11919 c:

A 75% yield of monoally ether of pyrocatechol (I) bp @ 1.5 torr 81°C was 
obtained by reaction of 100 g of pyrocatechol and 100 g of allyl chloride in 
anhyd. Me2CO with 15 g NaI and 106 g Na2CO3. A study of this reaction shows 
anhyd. Me2CO to be the best solvent; NaI is necessary for better yields [yields: 
68% with and 43% without NaI in PrOH; 46% with and 43% without in CH2OH2]."

And then the go on with the claisen rearrangement:

"When 100 g. I was heated 35-40 min at 160-170 deg C an exothermal reaction 
with temp. jump to 270 deg C took place, producing a liquid, which on fractional 
distillation, gave 35-8% 3,4-dihydroxy-1-allylbenzene (II) bp @ 1-2 torr 123-5°C, 
mp 48°C, and 47.5% 2,3-dihydroxy-1-allylbenzene bp @ 5 torr 95°C, mp 24°C."

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