Highly chemoselective reduction of N-Boc protected lactams

N-Boc protected lactams can be reduced chemoselectively in the presence of other groups such as esters, nitriles, carbamates or double bonds by first reducing the amide carbonyl group into the corresponding hemiaminal using lithium triethylborohydride followed by further reduction of the hemiaminal intermediate with triethylsilane/Boron trifluoride etherate. This method preserves the chirality present in the substrate.