A Practical Method for Selective Cleavage of a tert-Butoxycarbamoyl N-Protective Group from N,N-Diprotected α-Amino Acid Derivatives Using Montmorillonite K-10

A new, practical, and mild procedure for the selective cleavage of a tert‐butoxycarbonyl group (Boc) in N‐Boc‐N‐acyl‐diprotected amines is described. When applied to α‐amino acids, complete integrity of the stereochemistry was observed. The use of N,N‐di‐Boc‐α‐amino‐δ‐ and γ‐hydroxy esters provided both δ‐ and γ‐lactones in very good yields. The method is based on the use of Montmorillonite K‐10 either in CH2Cl2 at room temperature or in toluene at 65 °C and is compatible with the presence of a large range of functional and other protecting groups in the substrates. In most cases virtually pure samples are obtained after filtration and removal of solvents. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)