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This chapter delves into the realm of skeletal rearrangement reactions including Carbon-Carbon, Carbon-Nitrogen, and Carbon-Oxygen rearrangements. Topics covered include Wagner-Meerwein and Hofmann rearrangements, Baeyer-Villiger oxidation, and synthetic applications. It highlights the mechanism, conditions, and products of various rearrangements, essential for understanding the connectivity changes in carbon skeletons. The chapter provides insight into controlled rearrangements, rare anionic rearrangements, and Pericyclic reactions.
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Chapter 14Skeletal-Rearrangement Reactions • Carbon-Carbon Rearrangements • Carbon-Nitrogen Rearrangements • Carbon-Oxygen Rearrangements • Synthetic Applications • Summary
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
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
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
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
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
