Catalytic enantioselective electrophilic aromatic

Despite the prevalence and importance of atropisomerism in organic structures, the field of asymmetric catalysis has not yet recorded extensive success in the development of catalysts, which control this stereochemical feature. Indeed, catalytic reactions of this nature are presently rare and only modest atropi-somer selectivity has been observed. In this context. Miller s group recently developed the DKR of biaryl atropisomers via peptide-catalysed asymmetric bromination. The reaction proceeded via an atropisomer-selective electrophilic aromatic substitution reaction using a simple bromination reagent such as A7-bromophthtalimide. As shown in Scheme 5.27, a series of chiral bromi-nated biaryl compounds could be prepared with excellent enantioselectivities of... 

In the presence of 168 a (9mol%) and a phosphine oxide (Bu),P(O) and Ph2P(O)Me for aromatic and ahphatic aldehydes, respectively, 36 mol%), slow addition of TMSCN achieves excellent enantioselectivity with a wide range of aldehydes (86-100%, 83-98% ee). The Al complex has been proposed to work as a bifunctional catalyst for dual activation of the two reactants - the Lewis acidic Al center enhances the electrophilicity of aldehydes and the Lewis basic phosphine oxide induces cyanide addition by nucleophihc activation (Scheme 10.240). This catalytic asymmetric cyanosilylation has been used for the total synthesis of epothilones [652]. 

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