Boron tribromide → 5',7'-dimethyl-1'-(quinolin-2-ylmethyl)-3',4'-dihydro-1'H-spiro[cyclobutane-1,2'-quinolin]-6'-ol

6′-Methoxy-5′,7′-dimethyl-1′-(quinolin-2-ylmethyl)-3′,4′-dihydro-1′H-spiro[cyclobutane-1,2′-quinoline] (250 mg) was dissolved in CH2Cl2 (10 mL). At 0° C., 2.5 mL of BBr3 (2 mL, 1M solution in CH2Cl2) was added to the flask. The mixture was stirred at 0° C. for 20 minutes and then at room temperature for 30 minutes. After removing the solvent and BBr3, the reaction was quenched by adding into it water. The aqueous solution was then extracted with ethyl acetate (3×20 mL). The organic layer was combined, dried over Na2SO4 and evaporated. The residue was purified by column chromatography (silicagel, 12% ethyl acetate/hexane), giving 5′,7′-dimethyl-1′-(quinolin-2-ylmethyl)-3′,4′-dihydro-1′H-spiro[cyclobutane-1,2′-quinolin]-6′-ol as a dark yellow solid (26 mg). 1H-NMR (300 MHz, CD3OD) δ=8.10 (m, 2H); 7.72-7.92 (m, 2H); 7.74 (m, 2H); 6.00 (s, 1H); 4.83 (s, 2H); 2.76 (s, 6H); 2.32 (m, 2H); 2.07 (s, 5H); 2.00 (s, 3H); 1.94 (m, 2H); 1.72 (m, 2H) ppm. MS: (m/z)=359 (100, M+H+)