Production method of 1-Adamantyl-3-mesityl-4,5-dimethylimidazolium tetrafluoroborate contains 3 steps. The synthetic routes are as follows:

A. 3-(Mesitylamino)butan-2-one. A 250-mL, single-necked round-bottomed flask equipped with a -coated magnetic stir bar is charged with 3-hydroxybutan-2-one (13.2 g, 150 mmol, 1.5 equiv), mesitylamine (13.52 g, 100 mmol, 1.0 equiv), toluene (150 mL) and a catalytic amount of concentrated HCl (approximately 0.05 mL). The flask is then fitted with a Dean-Stark trap topped with a reflux condenser fitted with a nitrogen inlet. The solution is heated at reflux in a silicon oil bath for 3 h and the water generated is collected in the Dean-Stark trap (ca. 1.5 mL). The resulting yellow solution is allowed to cool to ambient temperature and the solvent is removed by rotary evaporation (25 °C, 8 mmHg). The oily residue is transferred to a 50-mL, one-necked, round bottomed flask and is purified by short path distillation under high vacuum (3 × 10^-2 mmHg) to give 16.72 g (81%) of 3-(mesitylamino)butan-2-one as a pale yellow oil, bp 94-98 °C.

B. N-Mesityl-N-(3-oxobutan-2-yl)formamide. An oven-dried, 100-mL, three-necked, round-bottomed flask equipped with two rubber septa, a nitrogen inlet and a Teflon-coated stir bar is charged with 3-(mesitylamino)butan-2-one (16.4 g, 80 mmol, 1.0 equiv) and anhydrous THF (25 mL). Acetic formic anhydride (10.6 g, 120 mmol, 1.5 equiv) is added in one portion to this solution, and the resulting mixture is stirred at ambient temperature for 22.5 h. The resulting brown mixture is transferred to a 100-mL, one-necked flask and is concentrated by rotary evaporation (25 °C, 8 mmHg) to a volume of approximately 20 mL before it is added on top of a wet-packed silica gel column (diameter: 7 cm, height: 22 cm, pre-treated with hexanes/EtOAc, 4:1). The product is eluted with hexanes/EtOAc, 3:1) to give 14.34 g (77%) of N-mesityl-N-(3-oxobutan-2-yl)formamide as a white, crystalline solid.

C. 1-Adamantyl-3-mesityl-4,5-dimethylimidazolium tetrafluoroborate. A 500-mL, three-necked, round-bottomed flask equipped with a pressure-equalizing dropping funnel, a nitrogen inlet, an internal thermometer, and a Teflon-coated stir bar (length: 4 cm) is charged with N-mesityl-N-(3-oxobutan-2-yl)formamide (13.7 g, 59 mmol, 1.0 equiv) and acetic anhydride (59 mL, 622 mmol, 10.6 equiv). The flask is immersed in an ice/water bath before aqueous HBF4 (48% w/w, 7.53 mL, 59.3 mmol, 1.01 equiv) is added dropwise through the addition funnel over a period of approximately 5 min to the stirred reaction mixture. Once the addition is complete, the resulting brown solution is stirred at ambient temperature for 3 h. Anhydrous Et₂O (400 mL) is then added, leading to the separation of 5-acetoxy-3-mesityl-4,5-dimethyl-oxazolinium tetrafluoroborate as a pale brown oil. The supernatant organic layer is carefully decanted and the residual oil is rinsed twice with Et₂O (2 × 200 mL). The remaining viscous oil is then suspended in toluene (100 mL). 1-Adamantylamine (11.54 g, 76.3 mmol, 1.3 equiv) is added and the resulting mixture is vigorously stirred at ambient temperature for 3 h. Addition of anhydrous Et₂O (200 mL) again causes the formation of two phases. The top Et₂O layer is discarded and the viscous bottom phase is carefully rinsed with anhydrous Et2O (2 × 200 mL) to remove excess adamantylamine. The resulting pale yellow semi-solid is suspended in toluene (150 mL) and then acetic anhydride (16.6 mL, 176.1 mmol, 3.0 equiv)  and aq. HBF4 (48% w/w, 2.24 mL, 17.6 mmol, 0.3 equiv) are introduced. The dropping funnel and internal thermometer are then replaced by a reflux condenser and a glass stopper and the mixture is stirred and heated to reflux in a silicon oil bath for 22 h. After reaching ambient temperature, the mixture is transferred to a one-necked flask, the solvent is removed by rotary evaporation (25 °C, 8 mmHg), the resulting brown syrup is triturated with anhydrous Et₂O (3 × 75 mL or until the ether layer is colorless), and the ether layers are discarded. The resulting white solid product is collected and dried under vacuum (0.2 mmHg) to give 14.87 g (58%) of pure 1-adamantyl-3-mesityl-4,5-dimethylimidazolium tetrafluoroborate. Crystals for elemental analysis are obtained by dissolving a sample of the product in a minimum amount of CH2Cl2 and careful layering of the resulting solution with anhydrous Et₂O (Et₂O/CH₂Cl₂, 7:1). The resulting solution is kept at ambient temperature for 3 d, resulting in the precipitation of 1-adamantyl-3-mesityl-4,5-dimethyl-imidazolium tetrafluoroborate as colorless prisms which are collected and dried under vacuum (0.2 mmHg).