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Synthese des Azocino[4.3‐ b ]indol‐Grundgerüstes von Strychnos‐Alkaloiden
Author(s) -
Fritz Helmut,
SoleymaniJamarani Mohammad,
Bats Jan Willem,
Teuber HansJoachim
Publication year - 1993
Publication title -
liebigs annalen der chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0170-2041
DOI - 10.1002/jlac.1993199301115
Subject(s) - chemistry , sodium hydride , strychnos , indole test , derivative (finance) , pyridine , benzophenone , stereochemistry , oxime , ring (chemistry) , medicinal chemistry , decarboxylation , carbazole , organic chemistry , catalysis , alkaloid , financial economics , economics
Synthesis of the Azocino[4.3‐ b ]indole Core Structure of Strychnos Alkaloids Michael addition of ethylmalonic dimethyl or diethyl ester with cyclohexenone and subsequent Fischer indole ring closure afford the (tetrahydrocarbazolyl)malonic esters 4a – c . Decarboxylation of 4a leads to the corresponding butyric acid methyl ester 5 which is oxidized by DDQ to the 4‐oxo derivative 6a (byproduct: carbazole 7 ). Oximation of 6a to 8a and acylation of the oxime group to 8b , c as well as hydrogenation of this group yield 9a , b . Subsequent hydrogenation of the tetrahydrocarbazole ring by means of borane/pyridine yields the hexahydrocarbazole derivatives 10a and b . By cyclisation in boiling o ‐xylene (sodium hydride catalysis) 10a is converted into the tetracyclic 1,5‐methanoazocino[4.3‐ b ]indole derivative 11a with an alkaloid analogous ethyl side chain. The X‐ray structural analysis of the corresponding phenylsulfonyl derivative 11b confirms constitution and stereochemistry. As a diastereoisomer of 11a the byproduct 11c could be isolated.