Christina Ullenius

Organocuprate addition to α,β-unsaturated compounds: synthetic and mechanistic aspects

A mechanistic model for the addition of lithium dimethylcuprate to enoates and enones is proposed on the basis of chemical and NMR-spectroscopic studies. The first step of the reaction is the reversible formation of a copper(

An NMR investigation of the reaction between cinnamic acid esters and lithium dimethylcuprate. Initial formation of an olefin-copper π-complex

alkene n-complex by coordination of the C-C group to one of the copper atoms in the dimeric cluster structure (Me Culi&. The following steps lead to the irre- versible formation of the new carbon-carbon bond. With chiral substrates two diastereomeric n-complexes are postulated, the stereoselectivity being determined by the relative rates for their irreversible decay. In the reaction between methyl S-ortho-dimethylaminoethylcinnamate, 10, and lithium dimethyl- and lithium diphenylcuprate the diastereomeric product ratios are ca 5: 1. 2

NMR Spectroscopic Investigation of the Adducts Formed by Addition of Cuprates to Ynoates and Ynones: Alkenylcuprates or Allenolates?

Abstract The reaction between lithium dimethylcuprate and methyl or t-butyl trans -cinnamate has been studied by 1 H and 13 C NMR spectroscopy in the temperature range −110 to +60°C. Below −35°C conjugate addition is slow, and a large shift in the olefinic hydrogen and carbon signals is observed. The temperature dependence of the spectra is interpreted in terms of two new species in slow equilibrium, one being an olefin-copper π-complex and the other involving complexation of lithium to the ester carbonyl oxygen. Above −35°C the lithium enolate from conjugate addition of the cuprate is formed, probably via the π-complex.

Reactions with lithium dimethylcuprate and lithium dimethylaurate : Solvent effects on the conjugate addition

Alkenylcuprates or allenolates–that is the question! The structures of the adducts formed by addition of cuprates to ynones and ynoates has been a matter of controversy for several decades. New NMR spectroscopic investigations with 13C-labeled substrates now reveal that there is no simple answer to the question. Some reactants give alkenylcuprates 1, others allenolates 2 as the most stable adducts. The transformations can be regarded as carbocupration of an alkyne rather than a Michael addition.

Stereoselectivity in the transfer of the 2-(1-dimethylaminoethyl)phenyl group, R*, from LiR* 2Cu and Li(R*) (2-thienyl)Cu to enones

Abstract The reaction of lithium dimethylcuprate with E -4-phenyl-3-buten-2-one in different solvents has been investigated. Fast conjugate addition occurs in hydrocarbons, dichloromethane and diethylether, while the reaction is retarded in better coordinating solvents. In highly polar solvents such as DMF or DMSO , no conjugate addition is observed. Dichloromethane- d 2 was chosen as a convenient solvent for NMR investigations of cuprates. The reaction of lithium dimethylaurate with different enones gave no conjugate addition products, but base induced self-condensation of enones

Addition of Me2CuLi to ortho-substituted methyl cinnamates an NMR study of the π-complex formation

Abstract One diastereomer is formed in large excess (98 – 76 % diastereomeric excess) on addition of the 2-(1-dimethylaminoethyl) phenyl group, R * , to 3-penten-2-one, 2-cyclohexenone, 4-phenyl-3-buten-2-one, and 5-phenyl-2,2-dimethyl-4-penten-3-one.

Indanetricarbonylchromium: the effects of 1-syn- and 1-anti substituents on the regioselectivity of nucleophilic addition. Crystal structures of 1-syn- and 1-anti- methoxyindanetricarbonylchromium

Abstract 1H and 13C NMR spectra of solutions obtained by mixing Me2CuLi, 1, or Ph2CuLi, 2, with methyl 3-[2-(1-methoxyethyl)phenyl]propenoate, 3, labelled in C2 (99% 13C), 3∗, methyl 3-(2-methoxymethylphenyl)propenoate, 4, methyl (S)-3-[2-(1-dimethylaminoethyl)phenyl]propenoate, 5, and methyl 3-(2-dimethylaminomethylphenyl)-propenoate, 6, in CD2CI2/THF in the temperature range −90°–+20°C have shown the formation of more than one copper-alkene π-complex from each enoate. The 13C labelled enoate 3∗ on addition to 1 forms at least four isomeric π-complexes as proved by the presence of four C2 signals around 52 ppm in the 13C NMR spectrum. Two dynamic processes have been observed, interconversion of different π-complexes and the reversible formation of the π-complexes, that lead to equilibrium mixtures of the copper-enoate species before carbon-carbon bond formation.

Intramolecularly assisted addition of LiMe2 Cu to methyl cinnamates

A series of diastereomeric syn and anti Cr(CO)3 complexes of 1-substituted indanes have been prepared by thermolysis of Cr(CO)6 or by arene exchange with naphthalene-Cr(CO)3 (3). The regioselectivity of nucleophilic addition of a-nitrile carbon nucleophiles to syn and anti 1-R-indane Cr(CO)3 complexes (R = OMe 4, Me 10) has been investigated and compared with that of analogous reactions with indaneCr(CO)3 (1). The results of an X-ray study of syn- and anti-4 are presented. Nucleophilic additions are shown to be sensitive to the steric and electronic effects of the benzylic substituent and the nucleophile. When the reaction mixtures are warmed to 0°C, equilibration of the regioisomeric cyclohexadienyl intermediates takes place.

Reversible addition of carbon nucleophiles to some nitrogen-substituted η6-arenetricarbonylchromium(0) compounds

Abstract Some ortho -substituted methyl cinnamates have been prepared and their reaction with lithium dimethylcuprate investigated. A methoxymethyl group in the ortho -position caused a ten-fold enhancement of the reaction rate relative to methyl cinnamate, while the corresponding nitrogen and sulphur ligands had only minor effects on the reactivity. A model for the transition state of the reaction is suggested.

Stereoselective addition of R2CuLi to ortho-substituted methyl cinnamates intramolecular assistance and solvent effects

Abstract A study has been made of the nucleophilic addition/oxidation reactions of η6-1-methyl-1,2,3,4-tetrahydroquinolinetricarbonylchromium(0) (1), η6-1-methylindolinetricarbonylchromium(0) (2), and η6-2-N,N-dimethylaminotoluenetricarbonylchromium(0) (3) with the nucleophiles 2-lithio-2-methyl-propionitrile (A), 2-lithioacetonitrile (B) and 2-lithio-2-methyl-1,3-dithiane (C). The regioselectivity in the addition of stabilized nucleophiles is time- and temperature-dependent, indicating the onset of thermodynamic control in prolonged/high temperature reactions. The addition is reversible, as indicated by crossover experiments with benzene-Cr(CO)3, the rate for dissociation of the Cue5f8C bond being strongly dependent on both the structure of the intermediate η5-cyclohexadienyltricarbonylchromium anions as well as the structure of the nucleophile. The regioselectivity of the addition/oxidation reaction can be optimized by an appropriate choice of reaction conditions for each of the compounds 1, 2 and 3.