Aryl aldimines, reduction

Coupling of aldimines.1 The Ti(II) reagent obtained from TiCl4 and Mg effects reductive coupling of aryl aldimines to 1,2-diarylethylenediamines as a 1 1 mixture of meso- and /-isomers. 

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]. 

CycUzations. In a catalytic process 2-aryl-3-alkenylindoles are generated from aldimines derived from o-alkynylanilines. Cyclization reactions of enynes and dienynes under reductive conditions (HCOOH)" or in the presence of aryl iodides to participate in a coupling process are useful. 

Indium chloride is known to have little water sensitivity and this has led to the discovery of a novel multicomponent synthesis of monocyclic 1,4-diazepines from aldehyde, amine, and a,p-xmsaturated ketone [89]. The initial step was the bimolecular reductive coupling of the aldimine formed in situ leading to the formation of N, N -diphenyl-l,2-diaryl-l,2-diamino ethane, which underwent aza-Michael addition to the a,p-xmsaturated ketone. The product 129 (Scheme 26) was isolated by simple recrystallization and obtained in very good yield witir excellent diastereose-lectivity favoring the trans-isomer. In the dimerization of tire radical Zn anion of aldimine, the repulsion of the lone pair on nitrogen and steric hindrance between the aryl groups seemed to have contributed toward frans-selectivity. 

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