Chapter 14 Skeletal-Rearrangement Reactions Carbon-Carbon Rearrangements Carbon-Nitrogen Rearrangements Carbon-Oxygen Rearrangements Synthetic Applications Summary

Chapter 14 Skeletal-Rearrangement Reactions Carbon-Carbon Rearrangements –Cationic Rearrangements 1,2 Hydrogen Shift, Wagner Meerwein alkyl migration, Pinacol –Anionic Rearrangements (rare, phenyl shift) –Pericyclic Rearrangements Molecular Orbital symmetry Previous examples Decarboxylation, and Diels-Alder Sigmatropic Shifts –1,5 Hydrogen and Carbon Shifts –1,3 Hydrogen and Carbon Shifts –3,3 Carbon Shifts (called Cope Rearrangement) Cope Rearrangement Electrocyclic Reactions

Chapter 14 Skeletal-Rearrangement Reactions Carbon-Nitrogen Rearrangements 3 common features –A good leaving group attached to the heteroatom –A free lone pair of electrons on the heteroatom –a migrating group on an adjacent atom –The Beckmann Rearrangement converts a ketone to an amide, under mild conditions, does not go to the -CO 2 H group mechanism is via a nitrilium ion, resonance stabilized with lone pair the larger group migrates 3º alkyl > 2º alkyl, aryl > 1° alkyl > methyl –The Hofmann Rearrangement converts a primary amide to primary amine, with one fewer carbon

Chapter 14 Skeletal-Rearrangement Reactions Carbon-Oxygen Rearrangements –The Baeyer-Villager Oxidation converts a ketone to an ester (or cyclic lactone) reagent is a peracid, such as CF 3 CO 3 H, CH 3 CO 3 H, or m-CPBA the larger group migrates (like the Beckmann rearrangement) 3º alkyl > 2º alkyl, aryl > 1° alkyl > methyl –The Claisen Rearrangement A Pericyclic rearrangement (like the Cope rearrangement) Occurs via a 6 membered cyclic intermediate

Chapter 14 Skeletal-Rearrangement Reactions Synthetic Applications –Review Table 14.1 p723 Using Rearrangements to Prepare Various Functional Groups Review of Reactions Review of Reactions from Chapters 8-14 –Review Table 14.2 Summary of Synthetic Methods, very important for next Chapter know reactant, product, reaction conditions and reagents Summary

Chapter 14 Summary Rearrangements result in changes in the connectivity in a carbon skeleton. Carbon-Carbon –Wagner-Meerwein, an alkyl group migrates, rearrangement via more stable intermediate (3º > 2º > 1º) –Anionic Rearrangements rare –Pericyclic Rearrangements controlled by molecular orbital symmetry rules (electrocyclic, cycloaddition and sigmatropic) Carbon-Nitrogen –Beckmann via nitrilium, converts oxime to amide, mild conditions, the larger group migrates 3º alkyl > 2º alkyl, aryl > 1° alkyl > methyl –Hofmann via isocyanate, converts amide to amine, one less carbon Carbon-Oxygen –Baeyer-Villiger, converts ketone to ester (lactone) with peracid, larger groups migrates 3º alkyl > 2º alkyl, aryl > 1° alkyl > methyl –Claisen, a Pericyclic reaction, like the Cope rearrangement