An efficient method for the transformation of naturally occurring monoterpenes into amines through rhodium-catalyzed hydroaminomethylation

The hydroaminomethylation (hydroformylation/reductive amination) of the naturally occurring monoterpenes, i.e., limonene, camphene, and β-pinene, was studied having as condensation counterparts the amines di-n-butylamine, morpholine or n-butylamine. Moderate to good yields (75–94%) were obtained employing [Rh(cod)(μ-OMe)]2 as pre-catalyst in the presence or not of triphenylphosphine or tribenzylphosphine as ancillaries in toluene, at 100 °C and 60 bar of an equimolar mixture of carbon monoxide and hydrogen. Some of the hydroaminomethylation products derived from limonene have biological activity and the products derived from camphene and β-pinene are new.

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► Naturally occurring monoterpenes were transformed into homologous amines.
► The transformation was made in one-pot (hydroaminomethylation).
► Rhodium complexes promote both hydroformylation and enamine hydrogenation.
► The concurrent double-bond isomerization was minimized by the use of phosphines.
► This study allowed insights about the nature of the catalytically active species.