Catalytic Hydroamination

Catalytic Hydroamination of Unsaturated Carbon-Carbon Bonds... 

Hydroaminomethylahon of alkenes [path (c)j wiU not be considered [12]. This review deals exclusively with the hydroaminahon reaction [path (d)], i.e. the direct addition of the N-H bond of NH3 or amines across unsaturated carbon-carbon bonds. It is devoted to the state of the art for the catalytic hydroamination of alkenes and styrenes but also of alkynes, 1,3-dienes and allenes, with no mention of activated substrates (such as Michael acceptors) for which the hydroamination occurs without catalysts. Similarly, the reachon of the N-H bond of amine derivatives such as carboxamides, tosylamides, ureas, etc. will not be considered. 

K. Tani and Y. Kataoka, begin their discussion with an overview about the synthesis and isolation of such species. Many of them contain Ru, Os, Rh, Ir, Pd, or Pt and complexes with these metals appear also to be the most active catalysts. Their stoichiometric reactions, as well as the progress made in catalytic hydrations, hydroal-coxylations, and hydrocarboxylations of triple bond systems, i.e. nitriles and alkynes, is reviewed. However, as in catalytic hydroaminations the holy grail", the addition of O-H bonds across non-activated C=C double bonds under mild conditions has not been achieved yet. 

Brunet, J. J. Neibecker, D. Catalytic Hydroamination of Unsaturated Carbon-Carbon Bonds. In Catalytic Heterofunctionalization, Togni, A., Griitzmacher, H., Eds. Wiley-VCH Weinheim, 2001 pp 91-141. 

Scheme 10. Catalytic hydroamination of phenylacetylene with aniline [30].

The displacement of cyclooctene or C2H4 from an iridium(I) centre by a variety of chiral phosphines (L) leads to the formation of [ (L)IrCl 2] which, in conjunction with a source of F (phosphazenium fluoride), has been used for catalytic hydroamination of olefins. This combination leads to a 6.5 fold increase in the activity of the system and a total reversal in the enantioselectivity compared to that of the chloride analogue. There is no direct evidence of formation of a metal fluoride complex, but it is proposed that it may well form in situ and that this might explain these interesting results [75]. 

Ge, S.Z., Meetsma, A., and Hessen, B. (2008) Neutral and cationic rare earth metal alkyl and benzyl compounds with the l,4,6-trimethyl-6-pyrrolidin-l-yl-l,4-diazepane Ugand and their performance in the catalytic hydroamination cyclization of aminoalkenes. Organometallics, 27, 5339. 

Catalytic hydroamination was reported for the cyclization of 4-alkenylamines in acidic medium in the presence of 0.1 molar equivalents of dipotassium tetrachloroplatinate15,16 however the reaction was sluggish and the catalytic turnover was low. 

Catalytic hydroamination of imsaturated carbon-carbon bonds has a strong potential for the access to a large variety of amines, enamines or imines [90]. The first addition of a N-H bond to alkynes catalyzed by a ruthenium catalyst was described in 1995 by Watanabe et al. [91], and involved a ruthenium-catalyzed addition of the N-H bond of N-formyl anilines to terminal alkyne (Scheme 8.29). 

Catalytic hydroamination of unsaturated carbon carbon bonds, particularly, in heterocycles 01MI40. 

Scheme 4 Catalytic hydroamination/cyclization of an aminoalkene with an internal double bond [104,125]...

To understand the function of the ionic ate complexes in the catalytic hydroamination reactions, the neutral yttrium chloro complex 212 containing diamide ligand L44 was prepared by the reaction of YCI3 with 1 equiv of Li2L44 to compare with the ate complexes. The neutral yttrium amido complex 213 was obtained from reacting 212 with LiNlPr2 in THF (Scheme 78). 

Unfortunately, the complexes underwent facile epimerization under the condi tions of catalytic hydroamination via reversible protolytic cleavage of the metal cyclopentadienyl bond (Scheme 11.7) [36, 38 40]. Thus, the product enantioselec tivity was limited by the catalyst s epimeric ratio in solution and the absolute configuration of the hydroamination product was independent of the diastereomeric purity of the precatalyst. Complexes with a (+) neomenthyl substituent on the cyclopentadienyl ligand generally produced the R) ( ) pyrrolidines, whereas ( ) menthyl and ( ) phenylmenthyl substituted complexes yielded the (S) (+) pyrrolidines, which is in agreement with the proposed stereomodel and solution studies on the equilibrium epimer ratios in the presence of simple aliphatic amines. 

Scheme 11.10 Catalytic hydroamination/cyclization of aminoalkenes using chiral amino thiophenolate yttrium complexes [61].

Scheme 11.11 Catalytic hydroamination/cyclization of aminoalkenes using 3,3 bisftrisarylsih substituted binaphtholate rare earth metal complexes [52].

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