Solid-phase synthesis of 4-aminopiperidine analogues using the Alloc protecting group:: an investigation of Alloc removal from secondary amines

A useful method for Alloc removal from secondary amines on solid-phase has been optimised. The use of Me2NH . BH3 (40 equiv., 40 min) as scavenger of the allyl cations in a palladium-catalysed process with Pd[PPh3](4) leads to quantitative removal of the Alloc group without any allyl back alkylation. Other scavengers such as morpholine or PhSiH3 are clearly inferior. Furthermore, this study has highlighted differences in the reaction kinetics of the deprotection step between secondary and primary amines such as those from alpha -amino acids. (C) 2001 Elsevier Science Ltd. All rights reserved.