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 CH 2 Cl 2 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)