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On the Mechanism and Stereoselectivity of the Copper(I)‐Catalyzed Cyclopropanation of Olefins − A Combined Experimental and Density Functional Study
Author(s) -
Bühl Michael,
Terstegen Frank,
Löffler Frank,
Meynhardt Bernd,
Kierse Stefanie,
Müller Michael,
Näther Christian,
Lüning Ulrich
Publication year - 2001
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 - 10.1002/1099-0690(200106)2001:11<2151::aid-ejoc2151>3.0.co;2-4
Subject(s) - cyclopropanation , chemistry , carbene , selectivity , copper , diazomethane , olefin fiber , density functional theory , catalysis , phenanthroline , medicinal chemistry , ethyl diazoacetate , stereoselectivity , aryl , computational chemistry , stereochemistry , crystallography , organic chemistry , alkyl
The mechanism of copper(I)‐catalyzed olefin cyclopropanation with diazomethanes has been studied at the BP86/AE1 level of density‐functional theory. For the model system Cu(diazabutadiene) + + ethene + diazomethane, copper carbene complexes are confirmed as viable intermediates, with rate‐determining barriers of the order of 25 kcal/mol (energies including zero‐point corrections) or 14 kcal/mol (when entropic contributions are included). For another model system, Cu(2,9‐dimethyl‐1,10‐phenanthroline) + + styrene + diazoacetate, very small anti / syn selectivities (resulting in trans / cis‐ cyclopropanes) have been found both computationally and experimentally. Cu(carbene) complexes with macrocyclic phenanthroline‐based ligands 1 (aryl bridgeheads and ether linkages) and 2 (calix[6]arene) have been optimized at the BP86/SDD level. A qualitative explanation for the trans selectivity observed with 1 , based on the tilted, cleft‐like conformation of 1· (CuCHCO 2 Me) + , is put forward. Similar conformations are found in structures of related acyclic mono‐ and diarylphenanthrolines (either free or complexed with Cu 2+ or Pd 2+ ), which have been determined by X‐ray crystallography. The observed cis selectivity of 2 is probably related to the fact that in 2· (CuCHCO 2 Me) + the calixarene macrocycle effectively blocks one hemisphere of the catalyst.