Synthesis of enantiomerically pure 1,5,7-trimethyl-3-azabicyclo[3.3.1]nonan-2-ones as chiral host compounds for enantioselective photochemical reactions in solution

The synthesis of the title compounds is described. As common starting material, 1,5,7-trimethyl-2,4-dioxo-3-azabicyclo[3.3.1]-nonan-7-carboxylic acid chloride (4) was employed which is in turn available from cis,cis-1,3,5-trimethylcyclohexane- 1,3,5-tricarboxylic acid (Kemp's triacid). For the synthesis of the diastereomeric menthyl esters 1 and 2, the chloride 4 was initially substituted by (-)-menthol and its imide part was subsequently reduced to an amide by consecutive treatment with sodium borohydride and triethylsilane. The enantiomerically pure hosts 3a and 3b were obtained from the racemate by resolution of their N-menthoxycarbonyl derivatives. The racemic compounds rac-3a and rac-3b were prepared from the acid chloride 4 and the ortho-hydroxyanilines 9a and 9b via amide formation, condensation to the oxazole and reduction. Structural data are provided which prove the absolute configuration of compound ent-3b and the relative configuration of compound, rac-3a.