Cp₂VCl₂-Catalyzed Meso-Selective Pinacol Coupling Reaction of Aldimines in the Presence of Chlorosilane and Zinc Metal

Abstract

A catalytic reductive coupling of aldimines was achieved by using a catalyst Cp2VCl2/PhMe2SiCl/Zn system. The influence of the catalyst, chlorosilane, co-reductant, solvent, and temperature on both the yield and diastereoselectivity of the coupling products was investigated in detail. As a result, the present Cp2VCl2-catalyzed reductive coupling of aldimines in the presence of PhMe2SiCl and zinc metal provided the corresponding 1,2-diamines in good yield with high meso selectivity (up to 92% meso), while the reductive coupling of aldehydes, ketones, and aldimines by the hitherto known catalytic methods leads to the preferential formation of dl isomers of the coupling products.

An Aldimine Cross‐Coupling for the Diastereoselective Synthesis of Unsymmetrical 1,2‐Diamines

“…In accordance with a chelated transition state, the anti-configurated products are predominantly formed, albeit with low diastereoselectivity: At best, an anti/syn ratio of 4.3:1 was observed. The relative configuration of the main products could be determined based on the reported characteristic 1 H and 13 C chemical shifts of vicinal diamines as well as the NOE data of the diastereomeric formaldehyde aminals of the diamines 4 a and 4 m. [19][20][21][22] In attempts to improve the diastereoselectivity of the reduction, we found that the reaction of the pure diimines 3 with BH 3 ·THF containing NaBH 4 furnishes preferentially the syn-configurated diamines 4 in quantitative yield (Table 2, Method A). Compounds of this type may be applied as combinatorially diverse pseudo-C 2 -symmetric N,N ligands for asymmetric aldol reactions, [23] dihydroxylations, [24] and reductions.…”

Eine gekreuzte Aldiminkupplung zur diastereoselektiven Synthese von unsymmetrischen 1,2‐Diaminen

“…Die Konfiguration der Hauptprodukte konnte mithilfe der in der Literatur beschriebenen charakteristischen 1 H-und 13 C-chemischen Verschiebungen sowie vergleichender NOE-Messungen an den diastereomeren FormaldehydAminalen der Diamine 4 a und 4 m zugeordnet werden. [19][20][21][22] Bei Versuchen zur Erhöhung der Diastereoselektivität der Reduktion fanden wir, dass über den Umweg einer Oxidation der Additionsprodukte zu den Diiminen 3 die synkonfigurierten Diamine 4 erhalten werden können, wenn [23] Dihydroxylierungen [24] oder Reduktionen [25] verwendet werden können. Setzt man bei der Reduktion mit BH 3 ·THF statt NaBH 4 Phthalsäure zu (Tabelle 2, Methode B), [26] entstehen hingegen die anti-konfigurierten Produkte.…”

Crystal Structure of (R*, R*)-N, N′-Di(4-bromophenyl)-1,2-di(2-hydroxyphenyl)-1,2-ethylenediamine•2DMSO

“…Few general routes exist for their diasteroselective preparations. 2 As part of our ongoing program it is of interest to study the crystal structure of the title compound ( Fig. 1).…”

“…The stereochemistry was assigned by comparing the resonances of the benzylic protons, as reported in the literature. 2 The molecular structure of the title compound appeared as shown in Fig. 2.…”