Synthesis of primary amines
Treatment of ketones with ammonia in ethanol and titanium(IV) isopropoxide, followed by in situ reduction with sodium borohydride allows a highly chemoselective reductive mono-alkylation of ammonia. A simple workup afforded primary amines in good to excellent yields. Reductive alkylation of ammonia with aldehydes afforded the corresponding symmetrical secondary amines selectively.
B. Miriyala, S. Bhattacharyya, J. S. Williamson, Tetrahedron, 2004, 60, 1463-1471.
By optimizing the metal hydride/ammonia mediated reductive amination of aldehydes and hemiacetals, primary amines were selectively prepared with no or minimal formation of the usual secondary and tertiary amine byproduct. The methodology was performed on a range of functionalized aldehyde substrates, including in situ formed aldehydes from a Vasella reaction.
E. M. Dangerfield, C. H. Plunkett, A. L. Win-Mason, B. L. Stocker, M. S. M. Timmer, J. Org. Chem., 2010, 75, 5470-5477.
The use of aqueous ammonia is essential for a palladium-catalyzed allylic amination for the preparation of primary amines. It is noteworthy that ammonia gas did not react at all. The first catalytic asymmetric synthesis using aqueous ammonia as a nitrogen source has also been demonstrated.
T. Nagano, S. Kobayashi, J. Am. Chem. Soc., 2008, 131, 4200-4201.
An experimentally simple Microwave-assisted reductive alkylation of methyl carbamate with a range of aldehydes provides, after basic work-up, structurally diverse primary amines. This method is particularly amenable to high-throughput synthesis.
F. Lehmann, M. Scobie, Synthesis, 2008, 1679-1681.
The synthesis of free α-chiral amines by a one-pot multicomponent procedure involves the formation of N-diphenylphosphinoylimines from commercially available starting materials and the subsequent enantioselective addition of diakylzinc reagents using an air-stable precatalyst complex.
Cote, A. B. Charette, J. Org. Chem., 2005, 70, 10864-10867.
An electrophilic amination of Grignard reagents with 4,4,5,5-tetramethyl-1,3-dioxolan-2-one O-phenylsulfonyloxime followed by acidic hydrolysis of the resulting imines gives primary amines.
M. Kitamura, T. Suga, S. Chiba, K. Narasaka, Org. Lett., 2004, 6, 4619-4621.