Enzymatic Resolution of 7,7‘-Dihydroxy-8,8‘- biquinolyl Dipentanoate and Its Conversion to 2,2‘-Di-tert-butyl-7,7‘-dihydroxy-8,8‘-biquinolyl

Incubation of (±)-7,7‘-di(pentanoyloxy)-8,8‘-biquinolyl (4) with a crude cholesterol esterase preparation (from bovine pancreas) yielded highly enantioenriched unreacted dextrorotatory material, (+)-(aR)-4 (46%, ≥99% ee), accompanied by the expected diol product, (−)-(aS)-7,7‘-dihydroxy-8,8‘-biquinolyl (1), in modest enantiomeric excess (≥37%, ≥77% ee). Treatment of scalemic diesters 4 with t-BuLi, followed by saponification in the presence of air, gave 2,2‘-di-tert-butyl-7,7‘-dihydroxy-8,8‘-biquinolyl (2) in enantio enriched form. Biquinolyl 2 is less configurationally stable than 1, racemizing rapidly in CHCl₃ (t_1/2(rac) = 1.9 h, rt), and with a moderate rate in MeOH (t_1/2(rac) = 30.5 h, rt).