The deprotection of benzyl ether (Bn-), allyloxycarbonyl- (Alloc-) and benzyloxycarbonyl (Cbz-) protected aromatic and aliphatic alcohols, and amines using commercially available a Ni-Al alloy or Pd/C-Al in water is described. The removal of protecting groups is carried out via hydrogenolysis under mild conditions using water as solvent and hydrogen source. The slow dissolution of Al in water results in the controlled, in situ formation of hydrogen gas and the additional metal component (Ni or Pd), serves as the hydrogenation catalyst. Although the deprotection of benzyl ethers can be performed using the Ni-Al alloy H2O system it did not perform well in the other examples. Switching to the Pd/C-Al-H2O allowed the deprotection of a broader range of starting materials (Bn-, Alloc- and Cbz-) under milder conditions. The reactions with Pd/C-Al-H2O are accomplished in high conversions and selectivities for various protected aromatic and aliphatic alcohols and amines. Eliminating the use of an explosive gas under pressure for the hydrogenolysis process, the absence of harmful waste and the use of water as reaction medium make this approach a safer, greener and more sustainable alternative to currently used methods. The general scheme of deprotection reactions is as follows:

Development of a new environmentally benign deprotection method using Pd/C-Al-H2O

256th National Meeting (2018)

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