Gabriel–Colman rearrangement

Gabriel–Colman rearrangement is a significant chemical reaction in organic chemistry, particularly in the synthesis of heterocyclic compounds. This rearrangement involves the transformation of phthalimide derivatives into ortho-aminobenzophenones through the action of strong bases. The reaction is named after the chemists Siegmund Gabriel and James Colman, who first reported the process in the early 20th century.

Overview

The Gabriel–Colman rearrangement is a versatile reaction that allows for the synthesis of complex aromatic compounds from relatively simple precursors. The reaction mechanism involves the deprotonation of a phthalimide derivative, followed by an intramolecular rearrangement, and finally, hydrolysis to yield the ortho-aminobenzophenone product. This reaction is particularly useful in the synthesis of pharmaceuticals and agrochemicals due to its efficiency and the broad availability of starting materials.

Mechanism

The mechanism of the Gabriel–Colman rearrangement begins with the deprotonation of the phthalimide derivative by a strong base, typically sodium hydride (NaH) or potassium tert-butoxide (KOtBu). This step generates a carbanion, which then undergoes an intramolecular nucleophilic attack on the adjacent carbonyl group. The resulting intermediate undergoes rearrangement to form a new carbon-nitrogen bond, leading to the formation of an imine or enamine intermediate. Hydrolysis of this intermediate under acidic or basic conditions yields the final ortho-aminobenzophenone product.

Applications

The Gabriel–Colman rearrangement has found widespread application in organic synthesis, particularly in the construction of complex aromatic compounds. Its ability to introduce amino groups ortho to carbonyl functionalities in benzophenones makes it a valuable tool in the synthesis of pharmaceuticals, dyes, and agrochemicals. Additionally, the reaction has been utilized in the synthesis of natural products and in the modification of steroids.

Variants

Several variants of the Gabriel–Colman rearrangement have been developed to expand its scope and applicability. These include modifications to the reaction conditions, such as the use of different bases or solvents, as well as the use of alternative substrates. These variants have enabled the synthesis of a wider range of compounds, including those with additional functional groups or stereochemical complexity.

See Also

• Phthalimide
• Aminobenzophenone
• Organic synthesis
• Rearrangement reaction