The Peterson Olefination

Like boron, silicon can be very useful in the synthesis of alkenes, as from a particular starting material - a β-hydroxysilane, both cis and trans alkenes can be made depending on whether the reaction is carried out in acid or base:

Acidic Conditions

NB - anti-periplanar elimination in the final step.

Basic Conditions

NB - syn-periplanar elimination in the final step. The final step is analogous to part of the Wittig Reaction.