Hydrogenation 2 aryl substituted quinolines

Binol-derived phosphoroamidite PipPhos (19) has been successfully used as a ligand for the Ir-catalyzed asymmetric hydrogenation of 2- and 2,6-substituted quinolines [39], 2- and 2,6-substituted quinoxalines [40], and IV-aryl imines [41] (Fig. 16). 

Catalyst 40 and 41 have been employed in the synthesis of a-substituted anti-a,P-diamino phosphonic acid derivatives [50] and P-amino acids [51], respectively. Subsequent modifications of the reaction conditions and catalyst structure (catalyst 42 in Figure 29.4) allowed also the synthesis of a-substituted xyn-a,P-diamino acid derivatives of phenylalanine [52]. Further studies, aimed at improving catalyst 40 activity by addition of over-stoichiometric amounts of triflic acid, led to catalysts such as 43, which showed increased effectiveness in promoting the addition of unactivated nitroalkanes to either electron-poor or -rich aryl N-Boc imines [53]. Although it seems that this type of catalysis is performed by activation through hydrogen bond, the concurrent intervention of the basic nitrogen of the quinoline moiety could not be ruled out... 

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