Hydroaminomethylation of eugenol with di-n-butylamine catalyzed by rhodium complexes: Bringing light on the promoting effect of Brönsted acids

The hydroaminomethylation of eugenol with di-n-butylamine was performed employing a bis[(1,5-ciclooctadiene)(μ-methoxy)rhodium(I)] as pre-catalyst. In the absence of phosphines, the catalyst was efficient in the process, but the regioselectivity for amines was poor. For phosphine-promoted catalyst, the chemoselectivity at the hydroformylation step improved, but the hydrogenation of enamine intermediates was hampered. The regioselectivity within the class of amines was surprisingly high (>96%) for the linear product. The addition of triflic acid (10–20 mol%) improved significantly the efficiency of HAM. Employing the 2,2′-bis((diphenylphosphino)methyl)-1,1′-binaphthyl as ancillary and triflic acid as a promoter, the linear product was obtained in up to 93% yield.

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► The hydroaminomethylation of eugenol is reported for the first time.
► New amines are produced with yields reaching 93%.
► Brönsted acids with non-coordinating anions are better promoters.
► Trifluoromethanesulfonic acid is an excellent promoter for hydroaminomethylation.