Tetrabenzyltitanium: An Improved Catalyst for the Activation of sp3 CH Bonds Adjacent to Nitrogen Atoms

A detailed study of intra‐ and intermolecular hydroaminoalkylation reactions by activation of CH bonds adjacent to nitrogen atoms performed with a number of different titanium‐based catalysts and the identification of tetrabenzyltitanium ([TiBn4], Bn=benzyl) as a preferred catalyst for practical synthetic hydroaminoalkylation procedures is described. In the presence of 5 mol % of this catalyst, geminally disubstituted and unsub‐ stituted primary 1‐amino‐6‐heptenes undergo selective cyclizations to 1‐amino‐2‐methylcyclohexanes. In comparison to [Ti(NMe2)4], improved yields are obtained with [TiBn4] for most of the substrates. Only in the case of the strongly Thorpe–Ingold‐activated 1‐amino‐2,2‐diphenyl‐6‐heptene is a better yield obtained with [Ti(NMe2)4], especially when the reaction is performed at 145 °C. Whereas secondary N‐aryl aminoalkenes undergo intramolecular hydroaminoalkylation with poor efficiency, the corresponding intermolecular reactions of N‐aryl amines with alkenes can be achieved in the presence of 10 mol % of [Ti(NMe2)4] or [TiBn4]. With two exceptions, [TiBn4] again turned out to be catalytically more active than [Ti(NMe2)4]. A number of reactions which can not be achieved at all with [Ti(NMe2)4] take place in the presence of [TiBn4], including the first successful transition metal‐catalyzed hydroaminoalkylation of styrene by a CH activation process.