Suzuki-Miyaura coupling stereochemistry

Suzuki-Miyaura Coupling. The Suzuki-Miyaura coupling reaction is very useful for construction of carbon-carbon bonds under mild conditions. Because it is tolerant of many functional groups, it has been employed widely in the synthesis of many natural products and related compounds. The stereochemistry of such coupling reactions proceeds with retention of configuration at both the C-X and C-(9-BBN) centers, confirmed recently hy independent studies from the groups of Woerpel and Soderquist. ... 

The Suzuki-Miyaura coupling joins an alkenyl or aryl borate with an alkenyl or aryl halide in the presence of a palladium catalyst. The stereochemistry of alkenyl reactants is preserved in the coupling. 

Suzuki-Miyaura coupling (Scheme 13.6). Detailed studies revealed that the transmetalation step is stereospeeifle and this step is likely to be stereochemistry determining. They also believe that the stereoselective transmetalation might oeeur either by a desymmetrization if both boronates are equivalent or by a dynamic kinetic resolution if the geminal boron atoms are not equivalent. 

Last but not least, theoretical calculations on the investigated asymmetric Suzuki-Miyaura coupling showed that the mechanism for the transmetalation step differs from the typical reaction pathway proposed in the literature. This is owing to the relative lability of the bis-hydrazone ligand, which can easy dissociate one of the N atoms directly coordinated to Pd. As far as the stereochemistry of the reaction is concerned, calculations so far do not provide an explanation for the high enantios-electivities observed in the experiments. Two possible reasons are either the true pathway for the reaction has not been identified yet, or an interconversion among... 

Suzuki-Miyaura cross-coupling polymerization of 1,4-bis((Z)-2-bromovinyl)benzenes with aryl-bis-boronic acids. The interest has been in an alternative approach, where rather than building a PPV with a pre-ordained stereochemistry, a postpolymerization yyn-selective reduction on a poly(phenylene ethynylene) (PPE) is used [125]. This scheme has the advantage that high molecular weight PPEs can be synthesized using either Pd-catalysis or alkyne metathesis. This route could also potentially allow for the access to an additional array of PPVs that are uniquely accessible from PPEs. The transformation of the triple bonds in PPEs and other acetylene building blocks to alkenes has considerable potential. 

As the overall cross-coupling reaction proceeds with inversion of stereochemistry and reductive ehmination is well known to undergo retention of stereochemistry, the result imphes that transmetaUation in this reaction proceeds predominantly with retention of stereochemistry. In addition to this study, in 1998, Woerpel and Soderquist [102] independently studied the stereochemistry of transmetaUation for the Suzuki-Miyaura cross-coupling reactions of alkyl boranes with aryl or alkenyl hahdes. Their deuterium labehng study revealed that the transmetaUation of alkyl boranes 163 or 166 proceeds with retention of stereochemistry to give products 165 or 167. Soderquist proposed a closed four-membered cyclic transition state 168 to account for the retention of stereochemistry observed during the reaction. 

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