Two-ligand catalysis

In the first experiments the two-ligand catalysis approach was followed /-butyldimethylphosphine borane, bispidine 137 and substoichiometric amounts (0.2 equiv.) of ( )-sp or Me-134. Later it has been found that the absence of the stoichiometric ligand (one-ligand catalysis) also lead to satisfactory results. " For example, an application of the catalytic enantioselective deprotonation can be seen in Scheme 5.55 (Table 5.21). 

A broad comparison between one- and two-ligand catalysis for the catalytic enantioselective deprotonation of phosphine borane 29 with either -BuLi or i-BuLi has been recently carried out by O Brien and co-workers (Scheme 5.56). In the two-ligand catalysis they employed bispidine 137, LiDMAE or A-methylmorpholine. 

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