Imines reductive coupling

Under the conditions of iridium-catalyzed hydrogenation, alkyne-carbonyl and alkyne-imine reductive coupling occurs in the absence of stoichiometric byproducts. For example, iridium-catalyzed hydrogenation of nonconjugated alkynes in the presence of ot-ketoesters delivers the corresponding a-hydroxy esters in... 

Oda S, Sam B, Krisehe MI (2015) Hydroaminomethylation beyond carbonylation allene-imine reductive coupling by ruthenium-catalyzed transfer hydrogenation. Angew Chem Int Ed 54 8525-8528... 

Scheme 2 Mechanism of the electrochemical or metal-promoted reductive coupling of imines in an acidic medium...

Schemes Sm-promoted reductive coupling of chiral C-aryl imines...

In the future, further studies should be addressed to improve the chemose-lectivity and diastereoselectivity of the reductive coupling process, especially searching for novel reagents and milder experimental conditions. As a matter of fact, a few novel reductive couphng procedures which showed improved efficiency and/or stereoselectivity have not been further apphed to optically active imines. For example, a new electrochemical procedure which makes use of the spatially addressable electrolysis platform with a stainless steel cathode and a sacrificial aluminum anode has been developed for imines derived from aromatic aldehydes, and the use of the N-benzhydryl substituent allowed 1,2-diamines to be obtained with good yields and dl-to-meso ratios... 

Moreover, a dramatic increase of the reaction rate was observed when the coupUng of aromatic imines mediated by samariiun diiodide was carried out in the presence of both water and a tertiary amine or tetramethylethylene-diamine (TMEDA) [29], causing the almost instantaneous formation of the 1,2-diamine, although with undetermined diastereoselectivity. Similarly, the samarium diiodide promoted reductive coupling of iminiiun ions formed in situ by reacting ahphatic aldehydes with secondary amines and benzotriazole occurred at temperatures as low as - 70 °C [30]. Even in this case a mixture of diastereomers with undetermined ratio was obtained nevertheless, the item of diastereoselectivity induced by a chiral amine (auxiliary) is worthy of investigation. 

An approach to the preparation of asymmetrically 1,2-disubstituted 1,2-diamines has been reported the zinc-copper-promoted reductive coupling of two different N-(4-substituted)phenyl aromatic imines, one bearing a 4-methoxy and the other a 4-chloro substituent, in the presence of either boron trifluoride or methyltrichlorosilane, gave a mixture of the three possible 1,2-diamines, where the mixed one predominated [31 ]. Low degrees of asymmetric induction were observed using 1-phenylethylamine, phenylglycinol and its 0-methyl ether, and several a-amino acid esters as the chiral auxiharies meanwhile the homocoupling process was not avoided (M.Shimizu, personal communication). 

The asymmetric synthesis of unsymmetrical vicinal diamines by samarium diiodide induced reductive coupling of nitrones derived from aUphatic aldehydes with optically pure N-tert-butanesulfinyl aromatic imines has been recently reported [41]. For example, the reaction between nitrone 55 and... 

The Cp2VCl2/R3SiCl/Zn catalytic system can be used for the reductive coupling of the imines 29 (Scheme 18) [55]. These components of the ternary catalyst are essential and, interestingly, meso-diastereoselectivity is observed in contrast to the coupling with cat. Cp2TiCl2/Sm system. The selectivity de-... 

Catalytic Reductive Coupling of Alkenes and Alkynes to Carbonyl Compounds and Imines Mediated by Hydrogen... 

Scheme 13 Enantioselective carbonyl (Z)-dienylation via reductive coupling of acetylene to aldehydes and imines mediated by hydrogen...

Ihmels H, Otto D (2005) Intercalation of Organic Dye Molecules into Double-Stranded DNA - General Principles and Recent Developments. 258 161-204 Iida H, Krische MJ (2007) Catalytic Reductive Coupling of Alkenes and Alkynes to Carbonyl Compounds and Imines Mediated by Hydrogen. 279 77-104 Imai H (2007) Self-Organized Formation of Hierarchical Structures. 270 43-72 Indelli MT, see Chiorboli C (2005) 257 63-102 Inoue Y, see Borovkov VV (2006) 265 89-146 Ishii A, Nakayama J (2005) Carbodithioic Acid Esters. 251 181-225 Ishii A, Nakayama J (2005) Carboselenothioic and Carbodiselenoic Acid Derivatives and Related Compounds. 251 227-246... 

Cyclization of 2-(l-alkynyl)XV-alkylidene anilines is catalyzed by palladium to give indoles (Equation (114)).471 Two mechanisms are proposed the regioselective insersion of an H-Pd-OAc species to the alkyne moiety (formation of a vinylpalladium species) followed by (i) carbopalladation of the imine moiety and /3-hydride elimination or (ii) oxidative addition to the imino C-H bond and reductive coupling. 

Reductive Coupling of Conjugated Enynes and Diynes with Activated Aldehydes and Imines... 

Reductive coupling of imines 43 (R1 = Me, Ph or 2-pyridyl R2 = Me, Pr, t-Bu or PI1CH2) in THF under the influence of a low-valent titanium species, produced by the action of magnesium amalgam on titanium(IV) chloride, gave the DL-diamines... 

The [lrCl(cod)]2-catalyzed reductive coupling of acrylates and imines provides trans-P-lactams with high diastereoselectivity (Equation 10.39) [67]. With regards to the reaction mechanism, in situ generated Ir-hydride reacts with acrylate 148 to produce an Ir enolate, which then reacts with the 147 to afford the P-amido ester 149. 

The following combinations have also been reported of titanium-mediated reductive coupling of imines TiCU-Mg in DME (or THF), TiCU-Li in DME (or THF), TiCU-EtjN in Catalytic use of... 

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