Squaric Acid Derivatives Prevent the Removal ofN-Cbz andN-Fmoc Groups under Catalytic Hydrogenation Reaction

Abstract

Under the catalytic hydrogenation conditions (H2/Pd-C), squaric acid derivatives 4 and 7 were found to be effective additives for chemoselective reduction of olefins and an alkyne having an N-Cbz or N-Fmoc group where the amino group remained to be protected. Benzyl esters having an N-Cbz or N-Fmoc group were also selectively removed to give the corresponding N-protected carboxylic acids.