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A New Enantioselective Total Synthesis of Natural Vincamine via an Intramolecular Mannich Reaction of an Silyl Enol Ether

✍ Scribed by Wolfgang Oppolzer; Hartmut Hauth; Paul Pfäffli; Roland Wenger

Publisher: John Wiley and Sons
Year: 1977
Tongue: German
Weight: 615 KB
Volume: 60
Category: Article
ISSN: 0018-019X
DOI: 10.1002/hlca.19770600533

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✦ Synopsis

Abstract

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.

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