Mannich-like three-component synthesis of α-branched amines involving organozinc compounds: ReactIR monitoring and mechanistic aspects

The infra-red spectroscopic in situ examination of the Mannich-like three-component reaction between organozinc reagents, amines and aldehydes is described, revealing that two distinct pathways are favored, depending on the nature of the starting amine. While reactions involving primary amines proceed via in situ-formed imines, reactions involving secondary amines rather imply a hemiaminal as the key intermediate species.

Graphical abstractThe infra-red spectroscopic in situ examination of the Mannich-like three component reaction between organozinc reagents, amines and aldehydes is described. It reveals that two different pathways are favored, depending on the nature of the starting amine.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► In situ infra-red examination of Mannich-like three-component systems involving organozinc reagents. ► Reaction of primary and secondary amines with benzaldehyde and organozinc species. ► Two different reaction pathways depending on the nature of the amine. ► An imine as the key intermediate with primary amines. ► A zinc alcoholate as the key intermediate with secondary amines.