Selective Removal of the Tert-butoxycarbonyl Group From Secondary-amines - Znbr2 As the Deprotecting Reagent

ZnBr2 in dichloromethane is a convenient reagent for mild and selective removal of the tert-butoxycarbonyl group from secondary amines. Among the available protections for the amino function, the tert-butoxy-carbonyl (t-Boc) group remains the most popular, owing to the convenience of its introduction and removal.1 There are several deprotecting conditions, adjustable to different chemical environments, but generally protic media or strong Lewis acids2 are recommended. We report here a new deprotecting reagent, ZnBr2 in dichloromethane, which removes t-Boc and is compatible with acidic sensitive functionalities, as exemplified for allylsilane 1 (scheme 1). When a carboxyethyl function (1a) was used as the nitrogen masking group, the expected heterocyclization to adduct 2a occurred in presence of ZnBr23, but if the t-Boc (1b) was present, in the same conditions the secondary amine 2b was obtained. © 1989, Taylor & Francis Group, LLC. All rights reserved.