Intermolecular hydroamination of oxygen-substituted allenes. New routes for the synthesis of N,O-chelated zirconium and titanium amido complexes

Abstract

Intermolecular hydroamination of heteroatom-substituted allenes with a bulky arylamine was carried out using a bis(amidate) bis(amido) titanium(IV) complex (1) as a precatalyst. The reaction of 2,6-dimethylaniline with oxygen-substituted allene 2c or 2d in the presence of complex 1 gives the ketimine regioisomer as the exclusive product. Reduction of such ketimine products resulted in the formation of amino ethers that were further employed as proligands for the formation of N,O-chelating five-membered titana- and zirconacycles. Such sterically demanding N,O-chelating ligands result in the high-yielding preparation of mono-ligated products. Solid-state molecular structures of all the complexes revealed distorted trigonal bipyramidal geometry about the metal centers, with a dative bond between the metal and the oxygen donor atom. These new complexes obtained using hydroamination as the key-step in ligand preparation were also shown to be useful cyclohydroamination precatalysts in their own right.

Transition‐Metal‐Catalyzed Hydroamination Reactions

“…In this case, only the branched product is observed (Table 15.5). These results show good selectivity for the branched product, and recent results show that even heteroatom-substituted allenes can be tolerated with this precatalyst [42]. While intermolecular allene hydroamination has been rarely reported, an interesting alternative is the investigation of intramolecular allene hydroamination.…”

“…Quinolines and their derivatives have been targeted using hydroamination routes over the past several years [351][352][353][354] and recent developments in the application of gold-catalyzed transformations, in particular, has furthered advances in one-pot and tandem approaches for the synthesis of these fused ring systems. In particular, Che and coworkers [355] showed that Au(I)-carbene complexes (42) can be used for tandem hydroamination-hydroarylation to prepare dihydroquinoline and quinoline products (Scheme 15.116). The use of aniline or indoline derivatives with microwave heating provides good yields in short reaction times.…”

Yttrium (amidate) complexes for catalytic C–N bond formation. Rapid, room temperature amidation of aldehydes

“…Amidate complexes of rare-earth and early transition metals have been shown to be effective catalysts for a variety of transformations. Rare-earth and group 4 (amidate) complexes can be used for the intermolecular and intramolecular hydroamination of alkynes, [29][30][31] allenes, 32,33 and alkenes. 29,[34][35][36][37][38][39][40][41] Simple amidate complexes can also promote hydroaminoalkylation in an intramolecular and intermolecular fashion.…”

Metal-Catalyzed Intermolecular Hydrofunctionalization of Allenes: Easy Access to Allylic Structures via the Selective Formation of C–N, C–C, and C–O Bonds

“…was observed by Schafer in 2011 with catalytic amount of zirconium and titanium amido complexes (Scheme 13). 45 Due to low stability of the formed imines, the latter were reduced with LiAlH4 to afford the corresponding amines. Using catalytic amount of AuBr3, Yamamoto reported in 2006 the first use of gold for the addition of various anilines to mono-and 1,3-di-subsituted allenes.…”