Primary amines from alkenes and carbonyl compounds: highly selective hydrogenation of oximes using a homogeneous Ru-catalyst

Abstract

The efficient production of aliphatic primary amines is still a major challenge despite their production on a large scale. Particularly when considering the overall production route starting from alkenes, current strategies suffer in at least one reaction step from poor regio- or chemoselectivity. This work presents an efficient and selective synthesis protocol for primary aliphatic amines via their corresponding aldoximes. These are readily produced from the condensation of hydroxylamine and the respective aldehydes. This straightforward condensation can be carried out either with isolated aldehydes or with crude reaction solutions from the hydroformylation of alkenes. It allows a straightforward separation of the aldoximes via their precipitation, which then serve as intermediates for the final reduction. In a newly developed protocol for aldoxime reduction, yields of up to 90% of the desired primary amines from several different aldoximes are achieved. The ruthenium/triphos catalyst system showed activities exceeding 7500 h⁻¹, which is significantly faster than other amination protocols, and complete conversion is achieved within minutes. Our approach allows the synthesis of the polyamide-12 precursor (methyl 12-aminododecanoate) from the unsaturated, renewable oleochemical methyl 10-undecenoate via the hydroformylation, condensation, reduction sequence on up to 6 g scale with up to 68% overall selectivity.