Arndt–Eistert reaction

[4] The preparation of the beta-amino acid from phenylalanine illustrates the Arndt–Eistert synthesis carried out with the Newman–Beal modification, which involves the inclusion of triethylamine in the diazomethane solution.

[8] Diazomethane is toxic and potentially violently explosive, which has led to safer alternative procedures,[9] For example, diazo(trimethylsilyl)methane has been demonstrated.

[13][14] In addition, primary diazoalkanes are very reactive, incompatible with acidic functionalities, and will react with activated alkenes including α,β-unsaturated carbonyl compounds to give 1,3-dipolar cycloaddition products.

An alternative to the Arndt–Eistert reaction is the Kowalski ester homologation, which also involves the generation of a carbene equivalent but avoids diazomethane.

The alpha-diazoketone (RC(O)CHN2) product undergoes the metal-catalyzed Wolff rearrangement to form a ketene, which hydrates to the acid.