Ammonium Chloride → 2,6,6-Trimethyl-1,4-cyclohexadiene-1-carboxaldehyde

(V where R1, R2, and R3 are methyl) To a solution of 2,6,6-trimethyl-2,4-cyclohexadiene-1-carboxaldehyde IV (3.70 g, 24.8 mmol) in anhydrous dichloromethane (25 mL) was added 1,8-diazabicyclo 5.4.0!undec7-ene (DBU) (0.150 mL, 0.98 mmol) in three (3) portions over 30 min. while the mixture was stirred at 0° C. The solution was warmed to room temperature and the progress of the reaction was monitored by TLC (hexanes:EtOAc 9:1). The two isomeric aldehydes are separable on TLC (RfSM 0.85; Rf product 0.75). After 60 min., the reaction was complete. A saturated solution of ammonium chloride (20 mL) was added, followed by dichloromethane (100 mL). The organic layer was separated and washed with a saturated solution of brine, dried over MgSO4 and concentrated. The residue was purified by silica gel chromatography (SGC) using a mixture of hexanes:EtOAc 15:1 as eluent to give 3.1 g of the desired aldehyde V (83% yield). IR (neat) 2960 CH), 1716 (C=O) cm-1 ; 1H-NMR (CDCl3 ; 400 MHz) δ (ppm): 10.18 (s, 1 H, CHO), 5.44, (m, 2 H, vinyl--CH), 2.81 (s, 2 H, --CH2 --), 2.12 (s, 3 H, CH3 ring), 1.25 (s, 6 H, 2×CH3 ring); 13C-NMR (CDCl3 ; 100 MHz) δ (ppm): 191.8, 152.1,138.4, 117.4, 35.6, 34.2, 28.1, 22.6, 18.47, 14.0.