Ozone → 7-Bromoheptanal

A solution of 8-bromo-1-octene (5.0 g, 0.026 mol) in 25 mL of MeOH and 5 mL of CH2Cl2 was cooled to -40° C. and treated with O3 while the mixture was cooled to -50 to -60° C. After 30 min the mixture turned bluish and after another 10 min of O3 treatment the mixture was purged with a stream of N2 for 5 min. With the mixture still at -50° C. and covered with a blanket of N2, 2.5 mL of dimethylsulfide was added. This mixture was stirred for 1 h at -40° C., 1 h at -20° C. and then allowed to warm to -10° C. over 1 h. A vacuum from the water aspiration was applied to remove some of the excess dimethylsulfide, and the residue concentrated further on a rotary evaporator (house vacuum). The residue was treated with 10 mL of water and this mixture was extracted with hexane; the organic extracts were washed with water, then brine, dried (MgSO4) and concentrated. A portion of the crude product (0.7 g) was chromatographed under pressure to give 7-bromoheptaldehyde: NMR (CDCl3) δ1.41 (m, 4H), 1.63 (m, 2H), 1.87 (m, 2H), 2.45 (m, 2H), 3.41 (m, 2H), 9.78 (s, 1H).