Practical synthesis of aminoethyl-o-carboranes

A convenient synthesis of [(N,N'-dibenzylamino)ethyl]-o-carboranes (3) is reported. Under catalytic hydrogenolysis conditions (H-2/Pd-C), o-carboranylamines with N-benzyl groups were selectively removed to give the corresponding secondary amines (4). Thus, a highly selective cleavage of one N-benzyl group was achieved by using Pd catalyst under mild and acidic reaction conditions. This method is efficient and compatible with other o-carboranyl alkyl groups such as methyl and phenyl groups present in the substrate. Alternatively, primary aminoethyl-o-carborane (7) can be prepared by monoalkylation of o-carborane, followed by selective deprotection of the silyl group.