RESUMO
Metal azides generated in situ by ion exchange exhibit divergent reactivity in reaction with cyclic N-alkoxy,N-siloxy-enamines. Depending on the nature of metal and the [M]/N3- ratio, addition of the azide ion to the C,C-double bond proceeds with regioselective cleavage of either exo- or endo-cyclic N-O bond leading to cyclic or open-chain α-azidooxime derivatives, respectively. Mechanistic studies in combination with solvent state FTIR spectroscopy and DFT calculations revealed that covalently bound metal azides (Co, Cu, Zn) transfer N3- anion to the C,C-double bond through a Lewis acid-assisted SN ' substitution of trialkylsilyloxy-group. More ionic metal azides (N1, Mg, Al, Sc, Ni, Yb) tend to react by initial nucleophilic attack of N3- anion on the silicon atom generating conjugated nitrosoalkenes. α-Azidooxime derivatives prepared by using the designed protocols were stereoselectively reduced to valuable 1,2-diaminoalcohols bearing up to four contiguous stereogenic centers. By reducing the α-azidooxime fragment in a stepwise manner site-selective protection and reductive amination of each of the emerging primary amino groups was achieved.
RESUMO
The synthesis of α-nitroxy-substituted oxime derivatives has been achieved by an unprecedented metal-assisted addition of a nitrate anion to bis(oxy)enamines, which are readily available from nitronates or nitroalkanes. The method has a broad scope and provides access to α-nitroxy-oximes and their cyclic ethers including nitroxy-substituted isoxazolines and dihydro-1,2-oxazines, which are of interest as potential NO-donors and intermediates in the synthesis of bioactive molecules.
