dear bees,
there are many routes to come to P2P's. The very common safrol-->isosafrole-->performic-->rearrangement-->MDP2P gives about 60% over all, the wacker processes drawback is the need for palladiumsalts. Some years ago there was discussed a procedure on the hive, going via the intermediate MDP2Pol (prepared from safrol and sulfuric acid). However, results didn't seem to be reproducible.
In an attempt to work out a simple route to P2P's, otto tried a two step procedure on eugenol methyl ether (3,4-dimethoxyallylbenzene) as follows:
addition of formic acid along the double bond[/br]
eugenol methyl ether (2 mL, 11.6 mmol) and formic acid (20 mL) were put into a pressure tube and kept at 120 degrees Celsius over night. The cooled mixture was partitioned between 20 mL of ethyl acetate and 50 mL brine. The organic phase was washed twice with bicarbonate solution untill no more CO2 evolves. Evaporation of the organic phase left 2.4 g of a reddish oil[1].
hypochlorite oxidation[/br]
the above product was dissolved in 20mL of ethyl acetate and some (~200 mg) PTC (benzyltrimethylamoniumchloride)was added. Then, a buffer solution (10 mL, phophate buffer pH 7) and bleach (10 mmol, ~1 equivalent) was added and the mixture was kept under heavy stirring for 30 minutes. At this time, stirring was discontinued and a sample for GC was taken from the upper layer [2]. Another 2 equivalents of bleach were added and after further 30 minutes a GC sample was taken again [3].
[1] Compare Kwart H, Drayer D (1974) J.Org.Chem. 39:2157-2166. on
https://www.thevespiary.org/rhodium/Rhodium/pdf/allylbenzene.hcooh.addition.pdf
The reddish oil shows one major peak in GC-MS having a mass of 224 which corresponds to the formate of 3,4-DMP2Pol. Some minor peaks (less than 3 area% each): another peak M=224 (supposingly the 3,4-DMP1Pol formate), a peak M=180 (the propylbenzene, some reduction occured?), a peak M=196 (3,4-DMP2Pol itself)
[2] Inspired by
https://www.thevespiary.org/rhodium/Rhodium/chemistry/ptc.naocl.oxidation.html
No other product than the 3,4-DMP2Pol (M=224) visible.
[3] Two peaks. Major 3,4-DMP2Polformate (M=224); minor M=258, typical Cl-pattern (supposingly 6-chloro-3,4-DMP2Polformate)
results[/br]
As shown in previous experiments, addition of HCOOH to 3,4-dimethoxyallylbenzene works nicely and in high yields (~90%). For hydrolysis of the formate, a simple water wash is not sufficient, the formate can be isolated by aqueous workup. The bleach oxidation method used will not work with esters, it might be useful however in aromatic chlorination.
Looking back on the discussions about oxidation of H2SO4-addition derived MDP2Pol (as in, for example Post No 108724)
, otto is in doubt, wether MDP2Pol was formed there at all. To him it looks like MDP2Pol hydrogen sulfate was produced all over.
otto
