Mechanistic Insights into the Reaction of Enantiomerically Pure Lithiosilanes and Electrophiles: Understanding the Differences between Aryl and Alkyl Halides

Abstract

AbstractThe reactivity of enantiomerically pure lithiosilanes against aliphatic and aromatic halo electrophiles has been investigated with the focus on product composition and enantiomeric ratios as a basis for a better understanding of ongoing mechanisms. Both parameters are strongly influenced by both the organic group and the corresponding halide of the used electrophile. Thus, high stereoselectivities and yields are only obtained if one distinct reaction mechanism dominates. In the case of aliphatic electrophiles, experimental and quantum chemical studies support the preference of an SN2 mechanism for chlorides resulting in retention of configuration on silicon, whereas bromides tend to react under inversion through a halide–lithium exchange (ate complex). For aromatic electrophiles these relationships change: chlorides and bromides both favor the formation of an ate complex over nucleophilic aromatic substitution, leading to inversion of configuration on silicon.