Pd-Catalysed Arylation of Secondary Phosphine Boranes

With 41b (R = t-Bu) the reaction was monitored by P NMR speetroscopy and stopped before it reached 50% conversion, to maximise the enantioselectivity in the kinetic resolution. The reaction is sluggish at room temperature but runs smoothly at 40 °C. Several typical bidentate ligands were tested and the results are listed in Table 6.11. 

Under these reaction conditions, several ligands give raeemic products (entries 1-5), including the DuPhos ligand, which had been successfully employed in similar reactions. In contrast, ligands of entries 6-9 gave more 

The diastereomeric ratio changes upon heating until thermodynamic equilibration is reached. The major diastereomer, with the absolute configuration p, was separated and characterised crystallographically. It seems that, at least 

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More recently, Livinghouse and co-workers studied the effect of Cu(I) on Pd-catalysed arylation of secondary phosphine boranes. Apart from a marked beneficial effect on the coupling elSciency, they discovered that Cu(I) is able to suppress the base-mediated racemisation of the phosphide borane intermediate, to generate a configurationally stable metallophosphide 47 (Scheme 6.22). Consequently, tertiary phosphine boranes 48 were obtained with retention of configuration, in good yields and excellent enantioselectivities. 

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