Gregor Kiefer

Atom‐Transfer Radical Addition Reactions Catalyzed by RuCp* Complexes: A Mechanistic Study

Kinetic and spectroscopic analyses were performed to gain information about the mechanism of atom-transfer radical reactions catalyzed by the complexes [RuCl2Cp*(PPh3)] and [RuClCp*(PPh3)2] (Cp*=pentamethylcyclopentadienyl), in the presence and in the absence of the reducing agent magnesium. The reactions of styrene with ethyl trichloroacetate, ethyl dichloroacetate, or dichloroacetonitrile were used as test reactions. The results show that for substrates with high intrinsic reactivity, such as ethyl trichloroacetate, the oxidation state of the catalyst in the resting state is +3, and that the reaction is zero-order with respect to the halogenated compound. Furthermore, the kinetic data suggest that the metal catalyst is not directly involved in the rate-limiting step of the reaction.

Olefin Cyclopropanation by a Sequential Atom-Transfer Radical Addition and Dechlorination in the Presence of a Ruthenium Catalyst†

Keywords: carbocycles ; cyclopropanes ; magnesium ; radicals ; ruthenium ; Gaba(C) Receptors ; Tert-Butyllithium ; Kharasch Reaction ; Copper-Complexes ; Reducing Agent ; Atrc Reactions ; Cyclization ; 1,3-Dihalopropanes ; Analogs ; Alpha,Omega-Dihaloalkanes Reference LCS-ARTICLE-2009-011doi:10.1002/anie.200904278View record in Web of Science Record created on 2009-09-28, modified on 2017-05-12

Oxidative Coupling Reactions of Grignard Reagents with Nitrous Oxide

Catalysis with laughing gas: N2O in combination with transition-metal catalysts allow the oxidative homo- and cross-coupling of Grignard reagents. The reactions can be performed under mild conditions despite the inert character of N2O.

1-Alkynyltriazenes as Functional Analogues of Ynamides.

The chemical reactivity of 1-alkynyltriazenes has been investigated and is found to parallel the reactivity of ynamides. The similarity in reactivity of these two classes of compounds is demonstrated by addition reactions with acids, by cycloaddition reactions with ketenes, tetracyanoethene, and cyclopropanes, as well as by intramolecular cyclization reactions. The presence of reactive triazene groups in the products enables subsequent transformations. Overall, our results suggest that 1-alkynyltriazenes should become valuable reagents in synthetic organic chemistry.

Divergent Asymmetric Synthesis of Polycyclic Compounds via Vinyl Triazenes

Vinyl triazenes were obtained by enantioselective [2+2] cycloaddition reactions of bicyclic alkenes with 1-alkynyl triazenes in the presence of a RuII catalyst with a chiral cyclopentadienyl ligand. These triazenes serve as unique vinyl cation surrogates. Under acidic conditions, the triazene functionality can be replaced with a variety of groups, including halides, alkoxides, sulfoxides, amides, arenes, and heteroarenes, thus providing efficient access to a pool of chiral polycyclic compounds.