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Influence of solvent polarity on the stereoselectivity of the uncatalyzed [4+2] cycloaddition of cyclopentadiene to an N , N ′‐fumaroyl bis‐(six‐membered ring [(2 R )‐10a‐homobornane‐10a,2‐sultam])
Author(s) -
Pia̧tek Anna,
Chapuis Christian,
Jurczak Janusz
Publication year - 2003
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.684
Subject(s) - chemistry , cyclopentadiene , stereoselectivity , cycloaddition , solvent effects , steric effects , solvent polarity , selectivity , stereochemistry , polarizable continuum model , ring (chemistry) , solvent , medicinal chemistry , computational chemistry , organic chemistry , catalysis
A new six‐membered ring (2 R )‐bornane‐10a,2‐sultam was tested as chiral auxiliary for the [4+2] cycloaddition of cyclopentadiene to the bis‐fumaroyl derivative (−)‐ 1f and shows under chelating conditions similar complete selectivity to Oppolzer's sultam. Inversion of the π‐face selectivity is nevertheless observed under uncatalyzed conditions under the influence of solvent polarity, varying from 82% de for the (2 R ,3 R ) cycloadduct 2f in trifluoroethanol to 70% de in favour of the (2 S ,3 S ) diastereoisomer in hexane as solvent. A predictive linear correlation is observed between the stereoselectivity and the solvent parameters according to the Abboud–Abraham–Kamlet‐Taft model. PM3 calculations allowed a rationalization of these results based on the transition‐state dipole moment. Illustrated by an x‐ray analysis of cycloadduct (2 S ,3 S )‐ 2f , the main structural differences and influences in terms of steric and stereoelectronic factors are discussed by comparison of the five‐ versus six‐membered ring homologues. Copyright © 2003 John Wiley & Sons, Ltd.