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Synthesis of Branched Tryptamines via the Domino Cloke–Stevens/Grandberg Rearrangement

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posted on 08.12.2016, 00:00 by Rinat F. Salikov, Konstantin P. Trainov, Anastasia A. Levina, Irina K. Belousova, Michael G. Medvedev, Yury V. Tomilov
The rearrangement of cyclopropylketone arylhydrazones generated in situ from arylhydrazine hydrochlorides and ketones leads to formation of tryptamine derivatives. The use of (2-aryl­cyclo­propyl)­ethanones in the reactions with model 4-bromophenylhydrazine hydrochloride gives branched tryptamines with aryl groups in the α-position to the amino group, while (2-methylcyclopropyl)­ethanone gives a mixture of α- and β-substituted products in a ratio of 1:3. The method was found effective in the synthesis of enantiomerically pure tryptamine. Thus, (R,R)-(2-phenyl­cyclo­propyl)­ethanone gives the (S)-α-phenyltryptamine derivative with an enantiomeric excess over 99%.