Anwendungsbreite der reduktiven Kupplung aromatischer Aldimin‐Derivate mit niedervalenten Titan‐Reagenzien zu 1,2‐Diarylethylendiaminen

Scope and Limitations of the Reductive Coupling of Aromatic Aldimine Derivatives with Formation of 1,2-Diarylethylenediamine Units, Using Low-Valent Titanium Reagents Besides the adducts from lithium amides to aromatic aldehydes, iminium salts, animals, and N-silylimines of aromatic aldehydes are coupled by the black suspension obtained from TiCL4 and Mg turnings in tetrahydrofuran (THF). The 1,2-diarylethylenediamines with tertiary and primary amino groups thus obtained are formed with no or only moderate diastereoselectivity (products 4a–d(Scheme 2) and 5–e(Scheme 3), respectively); the amine component may contain a strained ring or additional heteroatoms as in azetidin, bis(2-methoxyethyl)amine, piperazine, morpholine, and thiomorpholine (products 6a–e; Table 1). By an in-situ procedure, ethylenediamines exclusively trans-diaryl-substituted piperazine and perhydro-1,4-diazepine derivatives (products 7a–f; Table 2). Enantiomerically pure monocyclic trans,cis-5-alkyl-2,-3-diaryl-piperazines and diazabicyclo[4.3.0]nonanes and -[4.4.0]decanes are obtained by employing suitable diamines prepared from the amino acids (S)-alanine, (S)-phenylalanine, (S)-proline and from (S,S)- or (R,R)-cyclohexane-1,2-diamine, respectively (products 11a–i, 7e; Table 4). The configuration of all products are derived from the high-field NMR spectra, some of which are discussed in detail (Figs. 1 and 2, Tables 3 and 5); all new compounds are fully characterized by their physical data. Depending upon the structure of the components employed, the yields of purified products range from as low as 7% to essentially quantitative.