Hydroamination of allenes

The hydroamination of allene with morpholine or allylamines has been attempted with palladium-based catalysts. Usually, a mixture of 1 1 telomers (hydroamination products) and 1 2 telomers is obtained, the latter being the major [308, 309] or only... 

The [(T -C3H5)PdCl]2/dppf/AcOH catalytic system has been used for the bis(hy-droamination) of 3-alken-l-ynes to alkenic 1,4-diamines (Eq. 4.94), a reaction which seems to be mechanistically related to the hydroamination of allenes since an a-al-lenic amine CH2=C=CH(R )CH2NR2 is believed to be an intermediate [318]. 

A Pd(0) /benzoic acid system has been found to catalyze the hydroamination of certain arylalkynes with secondary amines, a reaction which is also mechanistically related to the hydroamination of allenes, affording high yields of aUyhc amines (Eq. 4.95) [319]. 

An interesting example of a gold-catalyzed cycloisomerization of P-aminoallene 168 to tetrahydropyridine 169 is depicted below <06OL4485>. Patil et al. report a similar gold-catalized hydroamination of allenes to produce 2-vinyl piperidine 170 in good yield <06TL4749>. 

Ackermann and Bergman developed a highly reactive titanium precatalyst for the intramolecular hydroamination of allenes 149 [101]. The products 150 and in one... 

Hydroamination of Allenes Different related amines can also be cyclized. The use of free amino groups led to long reaction times (several days), but sulfonamides, acetyl or BOc as protecting group led to fast conversion (in the latter case, problems of diastereoselectivity were observed). Optimization studies showed that, although cationic gold (I) complexes were not effective for these conversions, AuCI was a very good catalyst for these reactions. 

Initial studies by Yamamoto et al. developed a highly efficient gold-catalyzed intramolecular hydroamination of allenes under very mild conditions [42]. 

Hydroamination of allenes and 1,3-dienes in the presence of Ni(II), Pd(II), and Rh(III) complexes yields product mixtures composed of simple addition products and products formed by addition and telomerization.288 Nickel halides308 and rhodium chloride309 in ethanol [Eq. (6.51)] and Pd(n) diphosphine complexes310 are the most selective catalysts in simple hydroamination, while phosphine complexes favor telomerization 288... 

Cazes et al. reported the Pd-catalyzed intermolecular hydroamination of substituted allenes using aliphatic amines in the presence of triethylammonium iodide leading to allylic amines [19]. In a way similar to the Pd-catalyzed hydrocarbona-tion reactions we reported that the hydroamination of allenes [20], enynes [21], methylenecyclopropanes [22], and cyclopropene [10] proceeds most probably via oxidative addition of an N-H bond under neutral or acidic conditions to give allylic amines. The presence of benzoic acid as an additive promotes the Pd-medi-ated inter- and intramolecular hydroamination of internal alkynes [23]. Intramolecular hydroamination has attracted more attention in recent years, because of its importance in the synthesis of a variety of nitrogen-containing heterocycles found in many biologically important compounds. The metal-catalyzed intramolecular hydroamination/cyclization of aminoalkenes, aminodienes, aminoallenes, and aminoalkynes has been abundantly documented [23]. 

The enantioselective hydroaminations of allenes with chiral phosphine catalysts was accomplished with substrates that had a terminal symmetric substitution and with the amines protected as carbamates or sulfonamides. The same symmetric substituents were necessary for the enantioselective transformation nsing chiral counterions. However, very recently, high enantiomeric excesses were reached with trisubstituted asymmetric allenes by a dynamic kinetic enantioselective hydroamination of allenyl carbamates (eqnation 110), even thongh the E/Z ratio of the prodncts was not optimal. 

While no catalytic intermolecular asymmetric hydroamination of allenes has... 

The hydroamination of alkynes is a highly atom-efficient approach to the synthesis of enamines and imines, as well as to the synthesis of A-heterocyclic compounds such as indoles and pyrroles, which are widely occurring functional groups in biologically active molecules. Also included in this section is the hydroamination of allenes and alkenes, as the reaction of these substrates with chiral bimetallic catalysts has been shown to yield the chiral amine products with high enantioselectivity. 

Scheme 15.39 Hydroamination of allenes with transfer of chirality using an Au catalyst.

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 gold-catalyzed allene hydroamination, Bertrand has shown that the previously discussed cationic CAAC complexes for Au(I) (Table 15.17) are very important in the hydroamination of allenes with ammonia (Section 15.3.3) [179], and with both primary and secondary amines [235]. Notably, both aryl- and alkylamines can be used, and both 1,1-disubstituted allenes and monosubstituted allenes can be used as substrates to give allylamine products. In the case of monosubstituted allenes, mixtures of the T/Z diastereomers resulted. Depending on the amine substrate... 

Scheme 9.19 Intermolecular hydroamination of allenes and alkynes according to Bertrand and coworkers [38],...

Hydroamination of 7i-bonds is one of the most straightforward methods for the construction of C N bonds and, as such, has attracted a lot of attention. NHC- Au catalysts, in line with results obtained in hydration and hydroalkoxylation reactions (vide supra), proved highly efficient in this field and the inter-and intramolecular hydroamination of various alkenes," allenes," and alkynes" were reported with a number of NHC- Au complexes. Among these reports, Widenhoefer published an elegant bis-hydroamination of allenes, leading... 

LaLonde RL, Sherry BD, Kang EJ, Dean Toste, F. Gold(I)-catalyzed enantioselective intramolecular hydroamination of allenes. J. Am. Chem. Soc. 2007 129(9) 2452-2453. 

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