Stereospecific Peterson reaction (Base elimination - Diastereoisomer 1)
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In a base-promoted Peterson reaction the hydroxy group is deprotonated, and the oxyanion attacks the silicon atom intramolecularly. Elimination takes place via a syn-periplanar transition state. This is because the oxygen and the silicon are now bound together and it is the strength of this bond that drives the elimination forward. As was shown previously, the acid-promoted Peterson reaction of this diastereoisomer gives predominantly the E-alkene, whereas the base-promoted Peterson reaction produces the more sterically demanding Z-alkene.