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A New Enantioselective Total Synthesis of Natural Vincamine via an Intramolecular Mannich Reaction of an Silyl Enol Ether
Author(s) -
Oppolzer Wolfgang,
Hauth Hartmut,
Pfäffli Paul,
Wenger Roland
Publication year - 1977
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19770600533
Subject(s) - chemistry , intramolecular force , enantioselective synthesis , silyl enol ether , enol , mannich reaction , silylation , organic chemistry , stereochemistry , medicinal chemistry , combinatorial chemistry , catalysis
Natural Vincamine ( 1 ) has been synthesized in an enantioselective manner starting from the ethylpentenal 7 . In the key step a mixture of the diastereoisomeric racemates, 14 and 15 , was directly obtained from the silyl enol ether 11 and the dihydro‐β‐carboline 12 by the way of an intramolecular Mannich reaction of the intermediate 13 (Scheme 4) . The undesired stereoisomers, 14 and 15b , were recycled to 15a using the related reversible Mannich reaction 18 ⇄ 14 + 15 , followed by crystallization of the salt from 15a and (+)malic acid. 15a was converted to natural vincamine ( 1 ) in several steps including the known transformation 20→1 .