Synthesis of new mono-N-tosylated diamine ligands based on (R)-(+)-limonene and their application in asymmetric transfer hydrogenation of ketones and imines

A synthetic procedure leading to the preparation of a new family of enantiopure mono-N-tosylated-1,2-diamines derived from (R)-(+)-limonene is described. (+)-Limonene was transformed into the appropriate N-tosyl derivative using N-tosylaziridination based on chloramine-T trihydrate. Subsequent ring opening by sodium azide afforded the corresponding isomeric azides. Finally, reduction of the azide function gave enantiomerically pure mono-N-tosylated-1,2-diamines. The ligands obtained proved to be effective in the asymmetric transfer hydrogenation protocol on aromatic ketones and imines.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide

(1S,2S,5R)-N-(2-Azido-5-isopropenyl-2-methyl-cyclohexyl)-4-methyl-benzenesulfonamideC17H24N4O2S[α]D23=+3.9(c1,CHCl03)Absolute configuration: (1S,2S,5R)Source of chirality: (R)-(+)-limonene

(1S,2S,4R)-N-(2-Amino-4-isopropenyl-1-methyl-cyclohexyl)-4-methyl-benzenesulfonamideC17H26N2O2S[α]D23=+10.1(c1,CHCl3)Absolute configuration: (1S,2S,4R)Source of chirality: (R)-(+)-limonene

(1R,2R,5R)-N-(2-Amino-5-isopropenyl-2-methyl-cyclohexyl)-4-methyl-benzenesulfonamideC17H26N2O2S[α]D23=-40.0(c1,CHCl3)Absolute configuration: (1R,2R,5R)Source of chirality: (R)-(+)-limonene

(1S,2S,5R)-N-(2-Amino-5-isopropyl-2-methyl-cyclohexyl)-4-methyl-benzenesulfonamideC17H28N2O2S[α]D23=+1.1(c1,CHCl3)Absolute configuration: (1S,2S,5R)Source of chirality: (R)-(+)-limonene

(1S,2S,5R)-N-(2-Amino-5-isopropenyl-2-methyl-cyclohexyl)-4-methyl-benzenesulfonamideC17H26N2O2S[α]D23=+12.5(c1,CHCl3)Absolute configuration: (1S,2S,5R)Source of chirality: (R)-(+)-limonene