Novel (R)-(+)-limonene-derived ligands: synthesis and application in asymmetric transfer hydrogenations

(R)-(+)-Limonene was transformed into mono-N-tosylated-1,2-diamine derivatives using an N-tosylaziridination procedure followed by sodium azide treatment and reduction on Pd/C. The ligands obtained proved effective in the asymmetric transfer hydrogenation protocol on aromatic ketones.

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(1S,2S,4R)-N-(2-Azido-4-isopropenyl-1-methyl-cyclohexyl)-4-methyl-benzenesulfonamideC17H24N4O2S[α]D23=+4.9 (c 1, CHCl3)Source of chirality: (R)-(+)-limoneneAbsolute configuration: (1S,2S,4R)

(1R,2R,5R)-N-(2-Azido-5-isopropenyl-2-methyl-cyclohexyl)-4-methyl-benzenesulfonamideC17H24N4O2S[α]D23=-54.0 (c 1, CHCl3)Source of chirality: (R)-(+)-limoneneAbsolute configuration: (1R,2R,5R)

(1S,2S,4R)-N-(2-Amino-4-isopropyl-1-methyl-cyclohexyl)-4-methyl-benzenesulfonamideC17H28N2O2S[α]D23=+18.6 (c 1, CHCl3)Source of chirality: (R)-(+)-limoneneAbsolute configuration: (1S,2S,4R)

(1R,2R,5R)-N-(2-Amino-5-isopropyl-2-methyl-cyclohexyl)-4-methyl-benzenesulfonamideC17H28N2O2S[α]D23=-10.4 (c 1, CHCl3)Source of chirality: (R)-(+)-limoneneAbsolute configuration: (1R,2R,5R)