Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
Epimerization in Intramolecular Carbanilide Cyclization to Hydantoins: A Computational Study
Young-Dae GongSoo-Kyung KimSung-eun YooMark J. Kurth
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2002 Volume 75 Issue 11 Pages 2477-2480

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Abstract

An efficient and diastereoselective route for the synthesis of 2,5,6,7-tetrasubstituted-1H-pyrrolo[1,2-c]imidazoles has been developed using intramolecular azomethine ylide cycloaddition and carbanilide cyclization. Ab initio calculations at the 6-31G (d,p) basis set reveal that the thermal stability of diastereomers determine the epimerization during the intramolecular carbanilide cyclization (→ hydantoin). These stereochemical results are consistent with an endo-like cycloaddition of a trans,anti-azomethine ylide followed by base-mediated C7a-H epimerization (C7a-Hβ → C7a-Hα) to deliver the thermodynamically preferred trans,anti,trans-(Ha-Hb, Hb-Hc, Hc-Hd)-pyrrolidine stereochemistry (3) which is ca. 20.1 kJ/mol more stable than the trans,anti,cis-pyrrolidine stereochemistry. In the case of 2-hydroxy-1-naphthaldehyde, naphthalene ring steric effects result in a different stereochemical arrangement about each pyrrolidine ring.

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© 2002 The Chemical Society of Japan
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