On substituting TMCS by trimethylbromosilane (TMBS) high yields of α-bromoacetals are obtained, without added salts; starting from 1,1-dimethoxyhexane, for example, yields are 94% (84% starting from hexanal), while methylester is <1%. In this case, however, the reaction must proceed through an ionic mechanism since from norbornene the MnO 2 -TMBS reagent system gives a very complex pattern of products. Molecular bromine is very likely involved ...
