Asymmetric transfer hydrogenation of quinolines using tethered Ru(II) catalysts

The first report of an asymmetric transfer hydrogenation, in formic acid/triethylamine, of quinolines is described. Using a Ru(II) catalyst containing a 4-carbon tether, products of up to 73% ee were formed, whilst a Rh(III)-tethered catalyst gave products of up to 94% ee.

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N-((1R,2R)-2-(4-(3,5-Dimethylcyclohexa-1,4-dienyl)butylamino)-1,2-diphenylethyl)-4-methylbenzenesulfonamideC33H40N2O2See = 100%[α]D35=-5.3 (c 0.5, CHCl3)Source of chirality: enantiomerically pure starting material, (RR)-TsDPENAbsolute configuration: (1R,2R)

2-Methyl-1,2,3,4-tetrahydroquinolineC10H13Nee = 46%[α]D27=+46.7 (c 0.5, CHCl3)Source of chirality: asymmetric reduction of quinolineAbsolute configuration: (R)

2-Ethyl-1,2,3,4-tetrahydroquinolineC11H15Nee = 41%[α]D28=+35.6 (c 0.5, CHCl3)Source of chirality: asymmetric reduction of quinolineAbsolute configuration: (R)

2-Propyl-1,2,3,4-tetrahydroquinolineC12H17Nee = 42%[α]D24=+54.1 (c 0.5, CHCl3)Source of chirality: asymmetric reduction of quinolineAbsolute configuration: (R)

2-Butyl-1,2,3,4-tetrahydroquinolineC13H19Nee = 41%[α]D26=+46.6 (c 0.5, CHCl3)Source of chirality: asymmetric reduction of quinolineAbsolute configuration: (R)

2-Phenyl-1,2,3,4-tetrahydroquinolineC15H15Nee = 73%[α]D27=-31.3 (c 0.5, CHCl3)Source of chirality: asymmetric reduction of quinolineAbsolute configuration: (S)

2-Phenethyl-1,2,3,4-tetrahydroquinolineC17H19Nee = 50%[α]D25=+45.5 (c 0.5, CHCl3)Source of chirality: asymmetric reduction of quinolineAbsolute configuration: (R)

2-(3,5-Dimethoxyphenethyl)-1,2,3,4-tetrahydroquinolineC19H23NO2ee = 67%[α]D24=+39.5 (c 0.5, CHCl3)Source of chirality: asymmetric reduction of quinolineAbsolute configuration: (R)

2-(2-(6-Bromobenzo[d][1,3]dioxol-5-yl)ethyl)-1,2,3,4-tetrahydroquinolineC18H18BrNO2ee = 47%[α]D25=+25.6 (c 0.5, CHCl3)Source of chirality: asymmetric reduction of quinolineAbsolute configuration: (R)