Stereoselective Synthesis of 1,3-Diols Asymmetric Aldol Reactions

2 Stereoselective Synthesis of 1,3-Diols Asymmetric Aldol Reactions 

A slightly different sitrration is observed if Lewis adds ate required for the nucleophilic attack. The Mukaiyama aldol reaction is such an example. Here silyl enol ethers or ketene acetals are used in combination with Lewis acids. Recently an excellent analysis for the observed selectivities and transition state models was proposed by Wrest and Helquist [5]. In addition to the anti transition state, they could 

SCHEME 2.97 Ireland mechanism for the control of enolate formation. 

SCHEME 2.98 Zimmennan-Traxler transition state (substitution at boron atom has been removed for clarity). 

The synergistic effects of aU the described factors can even be slightly more complicated if the cyclic Zimmennan-Traxler 

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