BINOL-TiCl

The enantioselective aldol addition reactions mediated by BINOL/TiCl (Ot-Pr)4, j complexes as catalysts are highly attractive because of the convenient accessibility of the catalyst components along with the unique substrate scope they display [130-135]. These were developed by Keck and Mikami. Two catalyst preparations, involving BINOL and either TiCl2(Oi-Pr)2 [130] or Ti(Oi-Pr)4 [133], have been dociunented. Both of these furnish aldol adducts with excellent yields and enantioselectivities (Scheme 4.31). The fact that these compounds can mediate aldol additions to a wide range of functionalized aldehydes, such as trifluoroacetaldehyde [132] and chloroacetalde-hyde [131], is impressive, as these are rare substrates in catalytic, enantioselective aldol addition reactions (Scheme 4.32). Additionally, aldehydes such... 

Cyanosilylation. The chiral titanium reagent, prepared from the lithium salt of BINOL with TiCL, has been used as a catalyst for the asymmetric addition of cyanotrimethylsilane to aldehydes. In the example shown, the cyanohydrin is obtained with <82% ee (eq 9). 

Reetz et al. reported that a chiral Ti complex prepared from TiCL). and the dilithium salt of (S)-BINOL promoted the aldol reaction of 3-mefhylbutanal with KSA 48 with only poor enantioselectivity (60%, 8% ee) [115 b]. After this pioneering work, the titanium-based catalyst system has been intensively improved to attain an efficient catalytic cycle and high stereoselectivity [147-155]. 

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