Phosphine ligands PPh

The palladium-phosphine-catalyzed cycloaddition reactions of vinyloxetanes 530 with aryl isocyanates or diaryl-carbodiimides led to 4-vinyl-l,3-oxazin-2-ones 531 or l,3-oxazin-2-imines 532, respectively (Scheme 101). In the absence of phosphine ligands (PPhs, bis(diphenylphosphino)ethane (DPPE), l,3-bis(diphenylphosphino)propane (dppp), no conversion of heterocumulenes was observed. Starting from fused-bicyclic vinyloxetanes, both types of cycloadditions proceeded in a highly stereoselective fashion, affording only the r-isomers of alicycle-condensed 1,3-oxazine derivatives <1999JOC4152>. 

Polymer-supported triphenylphosphine (Ps-PPh2) has attracted much attention as a ligand for immobilization of metal complexes, as it is the supported analog of the ubiquitous simple tertiary phosphine ligand PPhs- Also, it is commercially available from a range of suppliers. 

In 1973, Mizoroki and coworkers [7] extended their preliminary work (Scheme 1.5) to aryl bromides however, these were found to be considerably less reactive than aryl iodides Phi > PhBr PhCl. Palladium black was identified to be more efficient than PdCl2. The use of a phosphine ligand PPhs was mentioned as being slightly beneficial [7]. This was the last contribution of the Japanese group to those reactions. 

DPPP) also had the desired effect of increasing the reaction yield, affording 38 % of 149 at 65 °C (Table 7.3, Entry 4) and 70 % at 1(X) °C (Table 7.3, Entry 5). The use of the monodentate phosphine ligands PPhs and PCys (Table 7.3, Entries 6 and 7) led to no reaction and trace prodnct formation, respectively. Whilst the reasons for this are unclear, similar detrimental effects on yield have been reported with these ligands in the palladium-catalysed cyanation of aryl chlorides [50]. 

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