Cationic organoaluminum compounds as intramolecular hydroamination catalysts

Cationic dialkylaluminum and m-terphenylalkylaluminum compounds catalyze the intramolecular hydroamination of primary and secondary aminopentenes. The reaction rates are strongly dependent on the substrate and the catalyst substituents. The bulky species [Dipp∗AlEt][CHB11H5I6] (Dipp∗ = 2,6-Dipp2C6H3–, Dipp = 2,6-iPr2C6H3–), 4, was the most active catalyst. Although the neutral species DcpAlEt2 (Dcp = 2,6-(2,6-Cl2C6H3)2C6H3–), 7, and Dipp∗AlEt2, 8, showed some catalytic activity, they were more than 25 times less reactive than their cationic counterparts [DcpAlEt][CHB11H5Cl6], 3, and 4. The cyclization of secondary benzylaminopentenes with [Et2Al][CHB11H5I6], 1, was strongly dependent on the substitution of the C-2 olefinic carbon.

Cationic low-coordinate organoaluminum compounds catalyze the intramolecular hydroamination of aminopentenes. Bulky m-terphenyl substituents significantly increase the catalyst activities.Figure optionsDownload as PowerPoint slideHighlights
► Cationic low-coordinate organoaluminum compounds catalyze the intramolecular hydroamination of aminopentenes.
► Neutral organoaluminum compounds bearing bulky m-terphenyl substituents also catalyze this reaction albeit much slower.
► The catalysts can be prepared in situ.