Preparation of Pincer 4-Functionalized 2-Aminomethylbenzo[h]quinoline Ruthenium Catalysts for Ketone Reduction

Abstract

Reaction of 1-naphthylamine with ethyl benzoylacetate gives the corresponding benzoyl acetamide derivative 1, which undergoes cyclization to 4-phenylbenzo[h]quinolin-2(1H)-one (2) in the presence of H2SO4. Bromination with POBr3, followed by reaction with n-BuLi and DMF, gives 4-phenylbenzo[h]quinoline-2-carbaldehyde (4), which is converted to the corresponding oxime hydrochloride 5 with NH2OH·HCl. Hydrogenation of 5 catalyzed by 10% Pd/C (type 338) leads to 4-phenyl-2-aminomethylbenzo[h]quinoline hydrochloride (HCNNPh·HCl, 6) isolated in high yield. Similarly, the 4-methyl-2-aminomethylbenzo[h]quinoline derivative (HCNNMe·HCl, 12) is prepared starting from 1-naphthylamine and 2,2,6-trimethyl-4H-1,3-dioxin-4-one, following the route for 6. Reaction of RuCl2(PPh3)3 with a diphosphine (PP), the HCl salt 6, and NEt3 in 2-propanol leads to the pincer complexes RuCl(CNNPh)(PP) (PP = Ph2P(CH2)3PPh2, 13; Ph2P(CH2)4PPh2, 14; 1,1′-bis(diphenylphosphino)ferrocene, 15). The methyl derivatives RuCl(CNNMe)(PP) (PP = P...