Chiral 8-Amino-5,6,7,8-tetrahydroquinoline Derivatives in Metal Catalysts for the Asymmetric Transfer Hydrogenation of 1-Aryl Substituted-3,4-dihydroisoquinolines as Alkaloids Precursors

Chiral diamines based on 8-amino-5,6,7,8-tetrahydroquinoline backbone, known as CAMPY (L1) or the 2-methyl substituted analogue Me-CAMPY (L2) were employed as novel ligands in Cp*metal complexes for the ATH of a series of substituted dihydroisoquinolines (DHIQs) known for being key intermediates in the synthesis of biologically active alkaloids. Different met-al-based complexes were evaluated in this kind of reaction, with rhodium catalysts, C3 and C4, proved most effective both in terms of reactivity and enantioselectivity. Although the modest enantiomeric excess values obtained (up to 69% ee in the case of substrate I), a satisfactory quan-titative conversion was successfully fulfilled even in the case of the most demanding hindered substrates when La(OTf)3 was used as beneficial additive, opening up the possibility for a ra-tional design of novel chiral catalysts alternative to the Noyori-Ikariya (arene)Ru(II)/TsDPEN catalyst.