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-Dipp(2)C(6)H(3)-, Dipp = 2,6-iPr(2)C(6)H(3)-), 4, was the most active catalyst. Although the neutral species DcpAlEt(2) (Dcp = 2,6-(2,6-Cl2C6H3)(2)C6H3-), 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. (C) 2011 Elsevier B.V. All rights reserved.