Intramolecular Hydroamination/Cyclization of Aminoallenes Catalyzed by Organolanthanide Complexes. Scope and Mechanistic Aspects

Organolanthanide complexes of the general type Cp‘ 2 LnCH(TMS) 2 (Cp‘ = η 5 -Me 5 C 5; Ln = La, Sm, Y, Lu; TMS = SiMe 3 ) serve as effective precatalysts for the rapid, regioselective, and highly diastereoselective intramolecular hydroamination/cyclization (IHC) of aminoallenes having the general formula RCH C CH(CH 2 ) n CHR‘NH 2 to yield the corresponding heterocycles (R = CH 3, n -C 3 H 7, n -C 5 H 11; R‘ = H, CH 3, n -C 4 H 9, CH 2 CHCH 2 CH 2; n = 2, 3). The mono- and disubstituted pyrrolidines and piperidines produced bear an α-alkenyl functionality available for further synthetic manipulation. Kinetic and mechanistic data parallel organolanthanide-mediated intramolecular aminoalkene and aminoalkyne hydroamination/cyclization, implying turnover-limiting allene insertion into the Ln−N bond followed by rapid protonolysis of the resulting Ln−C bond. The reaction rate is zero-order in [aminoallene] and first-order in [catalyst] over 3 or more half-lives. Hydroamination/cyclization of monosubstituted aminoallenes (R = H; R‘ = H, CH 3; n = 1, 2) is less regioselective, with tetrahydropyridines being the predominant products.