Results from studies of the Arndt–Eistert homologation of N-methyl-α-amino acids with concomitant ester and amide formation is discussed. The applicability of the use of ultrasound was investigated in the Wolff rearrangement of diazoketones for the production of esters and amides. This methodology was then applied to a novel ‘N-methyl coupling’ that allows simultaneous β-amino acid formation. Conventional ‘PyBroP N-methyl couplings’ were also performed as a comparison to establish the validity of the method.