BINAP ligand amination reactions

Several studies were performed in order to establish the mechaiusm (5-7). The currently accepted mechartism, presented in Scheme 26.1 for the Pd(BINAP) catalyzed amination, involves the formation of a complex, Pd(BINAP)2 from a catalyst precursor (usually Pd(OAc)2 or Pd2(dba)3) and ligand this complex lies outside the catalytic cycle and undertakes dissociation of one BINAP to form Pd(BINAP) the following steps are the oxidative addition of the aryl halide to the Pd(BINAP), reaction with amine and base, and the reductive elimination of the product to reform Pd(BlNAP). 

Directed and Asymmetric Reduction The principles of directed and asymmetric reactions were first developed for hydrogenation, as discussed in Section 9.2. Asymmetric hydrosilation of ketones can now be carried out cata-lytically with rhodium complexes of diop (9.22). The new chiral ligand Et-duPHOS, made by Burk at du Pont, allows chiral amination of ketones via Eq. 14.50. Note how the use of the hydrazone generates an amide carbonyl to act as a ligand, as is known to favor high e.e. (see Section 9.2). Noyori s powerful BINAP ligand has been applied to a large number of asymmetric reactions. 

In another context, excellent enantioselective nickel-catalysed a-ami-nations of N-Boc-oxindoles with azodicarboxylates have been achieved by using chiral Schiff base nickel catalysts. BINAP ligands have also encountered success in asymmetric nickel-catalysed electrophilic a-aminations and also in combination with other metals such as palladium. On the other hand, the use of other sources of electrophilic nitrogen, such as nitroso compounds and iodinanes, in reactions catalysed by nickel has so far not been described. 

Helmchen and coworkers employed a,co-amino-1,3-dienes as substrates [51]. By using palladium complexes with chiral phosphino-oxazolines L as catalysts, an enantiomeric excess of up to 80 % was achieved. In a typical experiment, a suspension of Pd(OAc)2, the chiral ligand L, the aminodiene 6/1-90 and an aryltriflate in dimethylformamide (DMF) was heated at 100 °C for 10 days. Via the chiral palladium complex 6/1-91, the resulting cyclic amine derivative 6/1-92 was obtained in 47% yield and 80% ee (Scheme 6/1.23). Using aryliodides the reaction time is shorter, and the yield higher (61 %), but the enantiomeric excess is lower (67% ee). With BINAP as a chiral ligand for the Pd°-catalyzed transformation of 6/1-90 and aryliodide, an ee-value of only 12% was obtained. 

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