Late alkyne substrates catalysts

As in the P(III) chemistry above, both late metal (Pd) and lanthanide catalysts have been used for P(V)-H additions to alkynes, alkenes, aldehydes, and imines. In addition, titanium, aluminum, and zinc catalysts have been employed. Typical P(V) substrates include dialkyl phosphites P(0R)2(0)H and phosphine oxides PR2(0)H. 

Alkyne hydroamination has been extensively reviewed [3, 4, 10] and important contributions using late transition metals have been realized to give the Markovnikov-type products most typically. Interestingly, in 2007, Fukumoto reported a tris(pyrazolyl borate)rhodium(l) complex for the anti-Markovnikov hydroamination of terminal aUcynes with both primary and secondary amine substrates, although yields with primary amines are always reduced compared to those with secondary amines (Scheme 15.26). Desirable functional group tolerance is also noteworthy for this regioselective hydroamination catalyst [187]. 

At this stage, the hydroamination of both terminal and internal alkynes with primary and secondary amines can be achieved by judicious choice of substrate and catalyst. Notably, hydroamination with primary aUcylamines using late transition metals is rarely reported [187, 189-191], although the related reaction with anihne derivatives can be mediated by complexes of groups 9-12 metals. Once again, to reduce the nucleophilicity of the amine partner, protected amines are often used as alternative substrates. 

The development of catalytic methods for the hydroamination of nonactivated alkenes, allenes, and alkynes has received considerable attention in recent years [1]. These highly atom-economical processes allow direct access to industrially and biologically relevant classes of compounds such as amines, enamines, and imines from cheap and readily available starting materials. This has recently led to an ever-increasing range of molecular compounds that have been identified as catalysts for these transformations (Scheme 13.1). Whereas rare-earth catalysts have been found to be mainly active in intramolecular hydroamination, other catalysts - in particular those of the late transition metals - are frequently limited to the addition of weakly basic substrates (aniline, sulfonamides, carboxamides, etc.) to alkenes, alkynes, and allenes. 

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