One-pot synthesis of secondary and tertiary amines from R(+)-limonene by tandem hydroformylation/reductive amination (hydroaminomethylation)

In this work, we were able to synthesize, in good isolated yields, seven R(+)-limonene derived amines (five of that described for the first time) employing a rhodium catalysed hydroaminomethylation reaction. This protocol consists in an one-pot three step reaction: double bond hydroformylation, aldehyde/amine condensation and imine/enamine hydrogenation. Hydroaminomethylation, besides the high yields, has a high atom economy because just 1 mol of water is wasted per mol of limonene. Due to our catalytic optimizations, the reaction time was reduced from 48 h (described in the literature) to 10–24 h, as well as limonene isomerization was strongly minimized by the triphenylphosphine added.