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Chapter 14 Skeletal-Rearrangement Reactions

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

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Chapter 14 Skeletal-Rearrangement Reactions

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

  2. Chapter 14Skeletal-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

  3. Chapter 14Skeletal-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 -CO2H 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

  4. Chapter 14Skeletal-Rearrangement Reactions • Carbon-Oxygen Rearrangements • The Baeyer-Villager Oxidation • converts a ketone to an ester (or cyclic lactone) • reagent is a peracid, such as CF3CO3H, CH3CO3H, 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

  5. Chapter 14Skeletal-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

  6. 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

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