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Total Synthesis of the Spirocyclic Oxindole Alkaloids Corynoxine, Corynoxine B, Corynoxeine, and Rhynchophylline
Author(s) -
Wanner Martin J.,
Ingemann Steen,
van Maarseveen Jan H.,
Hiemstra Henk
Publication year - 2013
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201201505
Subject(s) - chemistry , oxindole , aldehyde , total synthesis , substituent , ring (chemistry) , allylic rearrangement , stereochemistry , organic chemistry , catalysis
Racemic total syntheses of four spirocyclic oxindole alkaloids are reported. The general starting material was an N ‐2‐butenylated 2‐hydroxytryptamine, which underwent a base‐mediated Mannich spirocyclisation with a functionalised aldehyde to generate the C‐ring. The second key step was a Pd‐catalysed cyclisation of an α‐keto ester enolate (in the original aldehyde) onto an allylic carbonate (in the N ‐substituent) to form the D‐ring. The stereoselectivities of the key steps were moderate, but the isomers were readily purified, so that the natural products could be conveniently prepared, three of them for the first time.