General procedure for the synthesis of N,3-dimethylbenzylamine:
1. 40% aqueous methylamine (4.3 mL, 55.1 mmol) was added to a methanolic (50 mL) solution of 3-methylbenzaldehyde (6.4 mL, 54.0 mmol).
2. After 20 minutes of reaction, the mixture was cooled in an ice bath and sodium borohydride (3.07 g, 81.1 mmol) was added in portions over 20 minutes.
3. The mixture was gradually warmed to room temperature and stirred overnight.
4. Upon completion of the reaction, the mixture was concentrated under reduced pressure and subsequently partitioned between water (100 mL) and dichloromethane (100 mL).
5. The aqueous layer was further extracted with dichloromethane (2 × 50 mL), all organic extracts were combined and washed with 2N hydrochloric acid (3 × 30 mL).
6. The aqueous layer was further washed with dichloromethane (50 mL) and subsequently adjusted to pH 12 with concentrated ammonia and extracted with dichloromethane (3 × 100 mL).
7. The organic extracts were combined, washed with brine, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to afford N,3-dimethylbenzylamine (5.46 g, 75% yield), which could be used in subsequent steps without further purification.
Product characterization: 1H NMR (300 MHz, CDCl3) δ 7.26-6.05 (m, 4H), 3.72 (s, 2H), 2.46 (s, 3H), 2.35 (s, 3H).
