Keck allylation reaction activation

Keck almost simultaneously reported two procedures using chiral titanium catalysts 6A and 6B for the enantioselective addition of allyltributyltin to aldehydes [11]. In the first procedure, the catalyst 6A is prepared from a 1 1 mixture of (R)-binaphthol and titanium tetraisopropoxide. The second procedure for the preparation of 6B, in contrast, requires a 2 1 mixture of BINOL, Ti(0 Pr)4, and a catalytic amount of CF3SO3H or CF3CO2H. Using 10 mol % of the catalyst 6A or 6B, a variety of aromatic, aliphatic, and a,P-unsaturated aldehydes are efficiently transformed into the corresponding optically active homoallylic alcohols with high enantioselectivity. An improved procedure was later published for the catalytic asymmetric allylation reactions using the 2 1 BINOL/Ti catalytic system [12]. 

Lipshutz and coworkers synthesized an optically active BINOL analog by copper-catalyzed intramolecular biaryl coupling and applied the complex with Ti(0 Pr)4 7 to Keck s asymmetric allylation [23]. In the reaction with benzalde-hyde or cyclohexanecarboxaldehyde, almost identical results were obtained with regard to both yields of isolated product and enantiomeric excesses. 

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