Boric Acid → 5,6-Dihydroxyindole

Participants

Reaction Steps

At the completion of the reaction, which will generally require from about 30 minutes to about 3 hours, preferably from about 45 minutes to about 2 hours, the reaction system may be acidified to a pH of about 5 or less, preferably about 4.5, by the addition of acetic acid. The reaction mixture is then extracted, preferably after filtration, with ether or dichloromethane one or more times, under a nitrogen gas atmosphere, to recover the product 5,6-dihydroxyindole. According to a particular feature of the invention, the isolated yield of 5,6-dihydroxyindole can be further increased by carrying out the isolation of the product 5,6-dihydroxyindole by adding to the acetic acid mixture a compound which will protect the hydroxy groups to give the product compound in a form which is more stable in air. For example, addition of acetic anhydride to the filtered mixture gives 5,6-diacetoxyindole on heating. It is also possible to form the borate ester ##STR8## by addition of boric acid to the acetic acid reaction mixture. Generally, any protecting group which is stable to acetic acid can be added to the filtered reaction mixture to give the protected 5,6-dihydroxyindole.

Provenance & Evidence