The coumarin→indole transformation—a method for preparing 4-halo-5-hydroxyindoles from coumarins
作者:Elia J. L. Stoffman、Derrick. L. J. Clive
DOI:10.1039/b914580j
日期:——
Readily accessible 3-alkoxycarbonyl-6-hydroxy-5-halocoumarins can be converted into 4-halo-5-hydroxyindoles by a sequence whose essential steps are conjugate reduction or conjugate addition, decarboxylation, lactone opening with ammonia, phenolic oxygen protection, Hofmann rearrangement to an N-Boc ethylamine, oxidation to a quinone and deprotection of the nitrogen. The resulting β-aminoethyl quinone cyclizes to a mixture of quinone imine and indole, and the imine tautomerizes to the indole spontaneously or on treatment with rhodium on alumina.