Reductive aldimine

Recently, Akiyama et al. reported an enantiocontrolled [3+2] cycloaddition of chirally modified Fischer alkenylcarbene complexes 180 with aldimines 181 under Lewis-acid catalysis (Sn(OTf)2) to afford enantiomerically pure 1,2,5-trisubstituted 3-alkoxypyrrolines 182 (Scheme 40) [121]. The mode of formation of these products 182 was proposed to be a [4+2] cycloaddition, with the complexes 180 acting as a 1-metalla- 1,3-diene with subsequent reductive elimination. Upon hydrolysis under acidic conditions, the enol ethers give the enantiomerically pure 3-pyrrolidinones 183 (Table 9). 

Reductive coupling of aldimines obtained from aromatic aldehydes and aromatic amines to generate vicinal diamines mediated by indium was carried out in aqueous ethanol (Eq. 11.59)." Small indium rods were used in this study. No side-product was observed due to unimolecular reduction. The presence of NH4CI was found to accelerate the reaction. The reaction fails completely in CH3CN, DMF, or wet DMF. The use of nonaromatic substrates also resulted in the failure of the reaction. 

More recently, Tamaru and co-workers reported nickel-catalyzed reductive coupling of dienes with in situ-generated aldimines from aldehydes and amines (Equation (88)).446,446a The reaction exhibits high regio- and diastereoselectivity. 

For use of conjugated enones as nucleophilic partners in catalytic intermolecular reductive couplings to aldimines, see ... 

The [Ir(cod)2]BARF complex also showed high catalytic activity in the hydrogena-tive coupling of alkyne with aldimines to lead to reductive couphng products, aUyl amines [69]. 

As mentioned above, iridium complexes are also active in the formation of amines via the hydrosilylation/protodesUylation of imines. In the presence of 2 equiv. of HSiEts, the cationic complex [lr bis(pyrazol-l-yl)methane (CO)2][BPh4] (C4) catalyzes the reduction of various imines, including N-alkyl and N-aryl imines and both aldimines and ketimmes. Excellent conversions directly to the amine products were achieved rapidly at room temperature in a methanol solution (Scheme 14.7) [53]. 

Reduction of acid amides leads to a series of reactions in which the aldimine is a key intermediate. Aldimines are reduced at much less negative potentials than amides. The relative amounts of amine 32 and aldehyde 33 products formed depend... 

S. K. Srinivasan, S. Narasimhan u. N. Venkatasubramanian, Adv. Catal. [Proc. - Natl. Symp. Catal.], 7th, 315-319 (1985) . .Selective Reduction of Aldimines by Formic Acid in the Presence of RhH(PPhj)4 . 

Reductive coupling of aromatic aldimines leading to vicinal diamines proceeds with SmU, and is strongly accelerated by addition of a catalytic amount of or a stoichiometric amount of Yb(OTf)3. In the former... 

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