Stereoselective Synthesis and Reactivity of Dienyl Zirconocene Derivatives
作者:Ilan Marek、Nicka Chinkov、Swapan Majumdar
DOI:10.1055/s-2004-829189
日期:——
Stereoselective dienyl zirconocene derivatives have been prepared via a tandem allylic C-H bond activation isomerization-elimination reaction. These reagents can be either trapped directly with electrophiles or transmetalated to copper to participate in several carbon-carbon bond formations. When the transmetalation is performed on allylic as well as vinylic zirconocene derivatives, the reaction occurs with inversion of stereochemistry of the dienyl system.
Vinyl-substituted (Z)-stilbenes are stereoselectively synthesised on treatment of 4-arylbuta-2,3-dien-1-ols with arylboronic acids in the presence of a rhodium(I) catalyst. The reaction proceeds through the regioselective addition of organorhodium(I) species across the aryl-substituted carbon–carbon double bond of the allene moiety and subsequent δ-elimination of Rh(I)–OH.
New Approach to the Stereoselective Synthesis of Metalated Dienes via an Isomerization−Elimination Sequence
作者:Nicka Chinkov、Swapan Majumdar、Ilan Marek
DOI:10.1021/ja027027y
日期:2002.9.1
Treatment of Cp2ZrBu2 with enol ether containing a remote double bond lead to conjugated metalated diene as single isomer via a tandem isomerization-elimination sequence. 2-Arylsulfonyl 1,3-dienes can also be used as a source of dienyl zirconocene derivatives, and the stereochemistry of the diene is dependent on the transmetalation reaction.
Stereoselective Preparation of Dienyl Zirconocene Complexes via a Tandem Allylic C−H Bond Activation-Elimination Sequence
作者:Nicka Chinkov、Swapan Majumdar、Ilan Marek
DOI:10.1021/ja036751t
日期:2003.10.1
zirconocene derivatives were easily prepared, as unique geometrical isomers, from simple non-conjugated unsaturated enolethers with (1-butene)ZrCp2 complexes. This new methodology is based on a tandem allylic C-H bond activation-elimination sequence and the mechanism has been mapped out by deuterium labeling experiments. The stereochemical outcome of this process was determined by addition of several electrophiles
Z- as well as E-isomers of 1,2-diarylbutadienes undergo Diels-Alder reactions with nitrosobenzenes regiospecifically, but the adducts have different structures (3 or 4, respectively) in both cases. From kinetic results it is concluded that the somewhat anomalous cycloaddition of the E-isomers is facilitated and directed by the intermediate formation of a CT-complex.