Chapter 14 SkeletalRearrangement Reactions CarbonCarbon Rearrangements CarbonNitrogen Rearrangements

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 p 723 • Using Rearrangements to Prepare Various Functional Groups • 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