[OH-].[Na+].P(Br)(Br)[Br:4].[CH3:7][C:8]1([CH3:15])[CH2:13][CH2:12][C:11](=O)[CH2:10][CH2:9]1.[C:16]([O-:19])(=O)C.[Na+]>CN(C)C=O.C(Cl)(Cl)Cl>[Br:4][C:11]1[CH2:12][CH2:13][C:8]([CH3:15])([CH3:7])[CH2:9][C:10]=1[CH:16]=[O:19]
A 3-necked round bottom flask equipped with a nitrogen inlet, a thermometer and an outlet connected to a scrubber containing a solution of 2M NaOH was charged with anhydrous chloroform (15 ml) and anhydrous N,N-dimethylformamide (2.5 ml (32.3 mmol). The solution was cooled to ˜3° C. (internal temperature) under nitrogen before phosphorus tribromide (2.8 ml, 30.0 mmol) was introduced dropwise at a rate so that the reaction was maintained at ˜3° C. After the addition was complete the reaction was allowed to warm slowly to ˜10° C. and then the temperature was raised to 70° C. where it was maintained for 30 min. The reaction was cooled to rt and 4,4-dimethylcyclohexanone (1.4 g, 11.1 mmol) was added slowly over 20 min. After the addition was complete the reaction was warmed to 70° C. and it was stirred for 1.5 h. The mixture was then cooled to rt and poured onto a solution of 4M sodium acetate (15 ml). The pH of the resulting solution was adjusted to ˜7 using a solution of 5M NaOH and the mixture was then extracted with heptanes (×5). The combined organic fractions were dried (Na2SO4), filtered and concentrated under reduced pressure to give 2-bromo-5,5-dimethyl-cyclohex-1-ene carbaldehyde as a yellow oil (1.4 g, 58%). 1H NMR (MeOD) □ 10.05 (1H, s), 2.82 (2H, m), 2.10 (2H, m), 1.59 (2H, t), 0.96 (6H, s).
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