The Peterson reaction is stereospecific
المؤلف:
Jonathan Clayden , Nick Greeves , Stuart Warren
المصدر:
ORGANIC CHEMISTRY
الجزء والصفحة:
ص689-690
2025-07-09
500
The stereospecificity of this elimination involving silicon arises because it is an E2 elimination proceeding via an anti-periplanar transition state. In principle, it can therefore be used to make single geometrical isomers of alkenes, the geometry depending on the relative stereo chemistry of the starting material. However, this use of the Peterson reaction is limited by difficulties in making diastereoisomerically pure starting materials.
There is another, complementary, version of the Peterson reaction that uses base to promote the elimination. The starting materials are the same as for the acid-promoted Peterson reaction. When base (such as sodium hydride or potassium hydride) is added, the hydroxyl group is deprotonated and the oxyanion attacks the silicon atom intramolecularly. Elimination takes place this time via a syn-periplanar transition state—it has to because the oxygen and the silicon are now bonded together, and it is the strength of this bond that drives the elimination forward.
The two versions of the Peterson reaction give opposite geometrical isomers from the same diastereoisomer of the starting material, so from any single diastereoisomer of hydroxy silane we can make either geometrical isomer of alkene product by choosing whether to use acid or base. The problem is still making those single diastereoisomers! you saw that anti-periplanar transition states are usually preferred for elimination reactions because this alignment provides the best opportunity for good overlap between the orbitals involved. Syn-periplanar transition states can, however, also lead to elimination—and the base-promoted Peterson reaction should remind you of the Wittig reaction, with its four-membered cyclic intermediate. It is with the Wittig reaction, and a detailed discussion of its stereoselectivity.
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