[CH:1]1([C:4]2[CH:9]=[CH:8][CH:7]=[C:6]([CH:10]3OCC[O:11]3)[N:5]=2)[CH2:3][CH2:2]1.S(O)(C1C=CC(C)=CC=1)(=O)=O.O>CC(C)=O.O>[CH:1]1([C:4]2[N:5]=[C:6]([CH:10]=[O:11])[CH:7]=[CH:8][CH:9]=2)[CH2:3][CH2:2]1A mixture of 2-cyclopropyl-6-[1,3]dioxolan-2-yl-pyridine (0.9 g, see subpart (b) above) and a catalytic amount of TsOH hydrate in a mixture of acetone (10 mL) and water (2 mL) was heated to reflux overnight until most of the starting materials were consumed according to TLC. It was then cooled down to room temperature and concentrated. The residue was dissolved in diethyl ether and washed with saturated sodium carbonate, and then water, and then dried over MgSO4 and concentrated. The concentrate was purified on silica gel column with 100% CH2Cl2 to yield 6-cyclopropyl-pyridine-2-carbaldehyde as a bright liquid (0.65 g, 94%). 1H NMR (CDCl3, 300 MHz), δ 9.90 (s, 1H), 7.58(m, 2H), 7.23 (m, 1H), 2.01 (m, 1H), 1.02-0.92 (m, 4H).
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