The use of Boc 2 O as a coupling agent in the homologation of N-urethane protected-α-amino acid to its β-homomers by the Arndt-Eistert method is described. The homologation gives good yields without racemization. The use of Boc 2 O as a coupling agent not only allows the easy scale up of the process but also it is cost effective. CO urethane); 1 H NMR (δ, CDCl 3 ): 0.9 (3H, J = 7.5, t), 0.93 (3H, J = 7.1, d), 1.32 (11H, m), 1.5 (1H, m), 4.24 (1H, m), 5.3 (1H, s) and 5.42 (1H, J = 8.3, d).Boc-D-isoleucyldiazomethane (II g). 1.55 g (5 mmol) of I g, after the reaction gave 1.18 g (92.5%) of II g; mp 85-86 ЊC; Anal. Calc. for C 12 H 21 N 3 O 3 (255.28): C, 56.45; H, 8.28; N, 16.45; Found C, 56.32; H, 8.30; N,16.50%; IR ν max. cm Ϫ1 2107 (CHN 2 ), 1700 (CO urethane); 1 H NMR (δ, CDCl 3 ): 0.9 (3H, J = 7.5, t), 0.93 (3H, J = 7.1, d), 1.3 (11H, m), 1.55 (1H, m), 4.24 (1H, m), 5.35 (1H, s) and 5.45 (1H, J = 8.3, d).