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High Asymmetric Induction in Lewis Acid‐Promoted Intramolecular Ene‐Type Reactions: A diastereo‐ and enantioselective synthesis of (+)‐α‐allokainic acid. Preliminary Communication
Author(s) -
Oppolzer Wolfgang,
Robbiani Christian,
Bättig Kurt
Publication year - 1980
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.19800630729
Subject(s) - chemistry , enantioselective synthesis , intramolecular force , yield (engineering) , lewis acids and bases , ene reaction , hydrolysis , asymmetric induction , diene , medicinal chemistry , organic chemistry , stereochemistry , catalysis , materials science , natural rubber , metallurgy
The monocyclic amino diacid (+)‐α‐allokainic acid 1 has been prepared enantioselectively from the ester of cis ‐β‐chloroacrylic acid and (−)‐8‐phenylmenthol by a series of four synthetic operations in over 15% yield. The crucial step is the intramolecular ‘ene‐type’ reaction of the ( Z )‐diene 4 which on treatment with a mild Lewis acid undergoes a highly accelerated, dia‐ and enantiostereoselective cyclization to give the pyrrolidines 6 and 7 in a ratio of 95:5 (Scheme 3). Subsequent ester hydrolysis regenerates the auxiliary chiral alcohol. Similar cyclization of the ( E )‐diene 5 furnished a 15:85 mixture of 6 and 7 showing an efficient reversal of the optical induction by variation of the enoate geometry.