Concentration effects in chelation controlled reactions

The diastereo selcctivities of addition reactions of allyltrimethylsilane to an α-benzyloxyaldehyde were found to be relatively insensitive to the amount of added TiCl 4 , and to the absolute concentration of the 1:1 aldehyde/TiCl 4 , complex. In contrast, diastereoselectivities of similar additions to a structurally related β-benzyloxyaldehyde were highly dependent on these variables.