Synthesis of allylic amines through the palladium-catalyzed hydroamination of allenes

Palladium(II) 3-iminophosphine (3IP) complexes: Active precatalysts for the intermolecular hydroamination of 1,2-dienes (allenes) and 1,3-dienes with aliphatic amines under mild conditions

“…Lastly, all attempts at hydroamination using Nmethyl aniline resulted in the rapid formation of Pd black without any detectable hydroamination products. So, overall the reactivity trend for the [(3IP Ar )Pd(allyl)]OTf catalytic system appears to favor more basic amines, in stark contrast with other known catalysts that have more success with the less basic amines [33,35,43]. Additionally, hydroamination product isolation was straightforward with excellent recovery (>80%) of the amines produced.…”

Transition‐Metal‐Catalyzed Hydroamination Reactions

“…Diastereoselective and enantioselective allene hydroamination can also be targeted; with advances in enantioselective catalysis using late transition metals being reviewed in Section 15. Gazes and Yamamoto [91,92] reported some of the first late-transition-metalcatalyzed intermolecular allene hydroamination reactions, and an extension of this work disclosed the application of Au(III) salts in the preparation of allylamines using arylamine substrates. Most importantly, using this catalytic system, axial chirality of the allene starting material could be transferred to the allylic amine products with good retention of enantiomeric excess (Scheme 15.39).…”

“…Indeed, steady advancement in the application of such late transition metals for these transformations has been realized and extensive examples of hydroamination with alkynes, allenes, dienes, vinyl arenes, and alkenes have been achieved in intra-and intermolecular transformations with variability in observed selectivities (both regio-and stereoselectivities) and proposed mechanistic profiles for these transformations. With late transition metals, the most common mechanistic proposals can be summarized into three broad categories: (i) nucleophilic attack on neutral π-complexes [87][88][89], (ii) nucleophilic attack on allylic complexes (including those derived from dienes and vinyl arenes) [69,[90][91][92][93][94][95][96], and (iii) insertion of C-C multiple bonds into metal-amide or metal-hydride bonds [97,98]. Common to late transition metal catalysts used for this transformation is the use of metal precursors with weakly coordinating counterions, such as TfO − or TsO − , presumably to accommodate the alkene/alkyne coordination that is required during the catalytic cycle.…”

Asymmetric Hydroamination

“…The high Markovnikov regioselectivity results from the electronically favored secondary insertion of the vinyl arene in the palladium hydride bond. Similar mechanistic models have been suggested for the late transition metal-catalyzed hydroamination of allenes [18][19][20], dienes [17,[21][22][23], and trienes [24]. Generally, the g 3 -allyl species were identified as the resting state of the catalyst during the hydroamination reaction, indicating that nucleophilic attack is rate determining [15,23].…”