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Stereospecific Side Chain Activation in Cyclobutadiene–Fe(CO) 3 Chemistry: A Theoretical and Experimental Study on the Structure and Configurational Stability of Cationic, Radical and Anionic Intermediates
Author(s) -
Pfletschinger Anja,
Schneider Ulrich,
Lex Johann,
Schmalz HansGünther
Publication year - 2007
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200700342
Subject(s) - chemistry , cationic polymerization , stereospecificity , reactive intermediate , racemization , proton affinity , computational chemistry , hydride , stereochemistry , medicinal chemistry , hydrogen , polymer chemistry , ion , organic chemistry , protonation , catalysis
The configurational stability of reactive intermediates (cation, radical and anion) derived from ethylcyclobutadiene–Fe(CO) 3 by formal abstraction of a hydride, a hydrogen atom or a proton from the pseudobenzylic position was investigated. Density functional calculations (Becke3lyp) predicted that all these reactive intermediates can be regarded as planar chiral structures having a significant configurational stability. The racemization barriers were calculated to be 38.8 kcal mol –1 for the cationic, 16.9 kcal mol –1 for the radical and 44.8 kcal mol –1 for the anionic intermediate. In an experimental part of the study, derivatives of the 1‐hydroxyethyl‐substituted complex, which was enantioselectively prepared by CBS reduction of the acetyl complex, were subjected to S N 1‐type as well as single‐electron‐transfer‐driven umpolung reactions. The observed stereospecificity of these transformations (retention of configuration) is in accordance with the predicted configurational stability of the involved reactive intermediates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)