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(−)‐Sparteine‐Mediated Asymmetric Intramolecular Carbolithiation of Alkenes: Synthesis of Enantiopure Cyclopentanes with Three Consecutive Stereogenic Centers
Author(s) -
Hoppe Dieter,
Woltering Michael J.,
Oestreich Martin,
Fröhlich Roland
Publication year - 1999
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/(sici)1522-2675(19991110)82:11<1860::aid-hlca1860>3.0.co;2-8
Subject(s) - stereocenter , cyclopentanes , chemistry , sparteine , enantiopure drug , intramolecular force , carbanion , electrophile , stereochemistry , deprotonation , medicinal chemistry , enantioselective synthesis , organic chemistry , catalysis , ion
An asymmetric intramolecular carbolithiation reaction was developed by combining the (−)‐sparteine‐mediated enantiotopos‐differentiating deprotonation and the anionic 5‐ exo‐trig cyclization. Achiral 6‐phenylhex‐5‐enyl carbamates were efficiently cyclized furnishing regio‐, diastereo‐ (dr >99 : 1), and enantioselectively (er >98 : 2) 1,2‐ trans ‐substituted cyclopentanes. The intermediate primary benzylic lithium‐carbanion pairs were – in spite of their configurative lability – diastereoselectively substituted by versatile electrophiles creating a third consecutive stereogenic center. Additionally, some 4‐functionalized 6‐phenylhex‐5‐enyl carbamates were also cyclized in high yield to provide enantiomerically pure cyclopentanes incorporating three adjacent stereogenic centers.