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A Model Study of Intramolecular Asymmetric Radical Cyclizations of α‐Ester and α‐Amide Radicals
Author(s) -
Yeh RuLong,
Jiaang WeirTom,
Tsai YeunMin
Publication year - 1997
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.199700039
Subject(s) - chemistry , intramolecular force , tributyltin hydride , amide , stereoselectivity , radical , malonate , conformational isomerism , ring (chemistry) , medicinal chemistry , camphor , hydride , asymmetric induction , stereochemistry , organic chemistry , enantioselective synthesis , molecule , catalysis , hydrogen
Starting from malonate, a practical route was developed for the synthesis of α‐phenylthio acid 3. Several chiral compounds including (‐)‐menthol, (‐)‐8‐pbenylmenthol and a camphor based oxazolidinone 8 reacted with 3 to give α‐phenylthio esters or amide. These sulfides cyclized efficiently when reacted with tributyltin hydride. Among the chiral auxiliaries used, 8‐phenylmenthyl group displayed moderate asymmetric induction (64% ee for cis ‐product and 40% ee for trans ‐product). Based on this results, a transition state model was proposed to explain the observed stereoselectivity. In this model, due to π,π‐orbital overlap of the phenyl ring and the carbonyl, the si ‐face of the most stable conformer of the radical was shielded. This controlled the carbon‐carbon bond formation to occur from the re ‐face.