The coumarin-->indole transformation--a method for preparing 4-halo-5-hydroxyindoles from coumarins.
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 beta-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.
Stoffman
Elia J L
EJ
Chemistry Department, University of Alberta, Edmonton, Alberta, Canada T6G 2G2.
Clive
Derrick L J
DL
D003374:Coumarins / Q000737:chemistry*; D003500:Cyclization; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D013237:Stereoisomerism
D003374:Coumarins; D007211:Indoles; C030374:indole; C030123:coumarin