Westphalen–Lettré rearrangement

Westphalen–Lettré rearrangement is a chemical reaction that involves the rearrangement of esters of phenols under the influence of strong bases. This reaction is named after the chemists who first described it, Westphalen and Lettré. The Westphalen–Lettré rearrangement is an important reaction in the field of organic chemistry, particularly in the synthesis of complex organic molecules.

Mechanism

The mechanism of the Westphalen–Lettré rearrangement involves the deprotonation of the phenolic ester by a strong base, leading to the formation of a phenoxide ion. This ion then undergoes intramolecular attack on the ester carbonyl group, resulting in the cleavage of the C-O bond and the formation of a new C-C bond. The final step is a protonation that leads to the rearranged product. The reaction is notable for its ability to form new carbon-carbon bonds, making it a valuable tool in the synthesis of complex organic molecules.

Applications

The Westphalen–Lettré rearrangement has found applications in the synthesis of various biologically active compounds and complex natural products. Its ability to efficiently create new carbon-carbon bonds makes it a useful reaction in the construction of complex molecular architectures found in many natural products and pharmaceuticals.

Conditions

The reaction conditions for the Westphalen–Lettré rearrangement typically involve the use of a strong base, such as sodium hydride (NaH) or potassium tert-butoxide (KOtBu), and a suitable solvent, such as dimethyl sulfoxide (DMSO) or tetrahydrofuran (THF). The reaction temperature and time can vary depending on the substrates and the desired products.

Limitations

While the Westphalen–Lettré rearrangement is a powerful synthetic tool, it does have limitations. The reaction's success is highly dependent on the nature of the substrate, particularly the leaving group and the stability of the intermediate phenoxide ion. Additionally, the reaction may compete with other base-induced processes, such as elimination or substitution, which can lead to a mixture of products.

See also

• Claisen rearrangement
• Wittig reaction
• Diels-Alder reaction