Alkylamines intermolecular hydroamination

Additional catalytic investigation of p-diketiminate scandium complexes by Piers and coworkers showed that well-characterized complexes 121 and 122 with the bulky ligand L27 were highly active catalysts for intramolecular hydroamination to form nitrogen heterocycles. The catalytic reaction was monitored by determining starting material and product with NMR. Both the neutral complex 121 and the CIP complex 122 are effective catalysts (10 mol%) for the intramolecular hydroamination of 5-phenyl-4-pentyl-l-amine (R = H, R = Ph, n = 1 in Scheme 42). However, they are not active catalysts for the potential application to the intermolecular hydroamination of 1-hexyne with alkylamines [82],... 

More recently, reactivity investigations have explored the scope of reactivity of previously developed catalysts. With respect to advances in group-lO-catalyzed allene hydroamination, Widenhoefer [229] explored Pt(II) neutral and cationic species for the intermolecular hydroamination of allenes with secondary alkylamines to make aUylamine products with excellent regioselectivity and diastereoselectivity (E/Z) (Scheme 15.43). This work builds upon a 2005 report for neutral Pt(II) compleiKs for the intermolecular hydroamination of alkenes with secondary amines [230, 231]. In the 2010 report, a variety of cyclic and acyclic alkylamines can be used as substrates, although neither arylamines nor primary amines are disclosed as substrates. This system is also limited to monosubstituted allenes. Consistent with long-standing proposals [231], outer-sphere addition of the amine to a cationic Pt(II) It-allene complex is proposed [229]. 

In 1999, Doye disclosed that dimethyltitanocene is a catalyst widely applicable to intermolecular hydroamination of alkynes with primary aryl- and alkylamines [302]. In the case of unsymmetrically substituted alkynes, the reaction occurs with high re-gioselectivity, forming the anti-Markovnikov products exclusively (Scheme 14.127). Kinetic studies suggest that the reaction mechanism involves the formation of a Ti-imido complex as the catalytically active species. Doye further developed a tandem Ti-catalyzed protocol of alkyne hydroamination and imine reduction, affording secondary amines in a fully catalytic one-pot reaction [303]. 

Schafer found that the bulky bis(amidate) complex is an effective catalyst for intermolecular hydroamination of terminal alkyl alkynes with alkylamines, giving exclusively the anti-Markovnikov aldimine product [309]. The same titanium complexes can also be utilized in the hydroamination of substituted allenes in good yields (Scheme 14.132). Under the catalysis of an imidotitanium complex, the highly strained methylenecyclopropane can undergo hydroamination reaction with either aromatic or aliphatic amines, to give ring-opened imine products in good to excellent yields and chemoselectivities [310]. 

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