Hydrogen Bromide → 1,2,3,6-Tetrahydro-1-methyl-4-(2,4,6-trimethoxyphenyl)-3-pyridinol

Participants

Reaction Conditions

Reaction Steps

75.7 ml (0.44 mol) of 33% strength HBr in glacial acetic acid were added to 100 ml of glacial acetic acid and 50 g (0.44 mol) of 1-methylpiperidin-4-one (III) were then rapidly added dropwise at 20-25° C. with ice cooling. 70.4 g (0.44 mol) of bromine were added dropwise at 20-25° C. under nitrogen in the course of 30 min to the suspension of the hydrobromide obtained in this way, a clear, yellowish solution being obtained. This was stirred at 25° C. for 60 min and 67.2 g (0.40 mol) of 1,3,5-trimethoxybenzene (V) were then added to the reaction solution. After 15 min, a further 40.8 g (0.4 mol) of acetic anhydride were added with cooling and the mixture was stirred at 25° C. for 1 h. After this, 750 ml of water were allowed to run in and the mixture was heated at 80° C. for 9.5 h. The reaction mixture was then cooled to 5-10° C. and adjusted to pH 5.5 by dropwise addition of 200 ml of conc. sodium hydroxide solution in the course of 30 min. In the course of this, unreacted 1,3,5-trimethoxybenzene precipitated. The suspension was filtered and the filtrate was adjusted to pH 14 at 5-10° C. using a further 200 ml of conc. sodium hydroxide solution. In the course of this, the allyl alcohol (VII) initially precipitated in slightly oily form, but on longer stirring became solid and could then be readily filtered off with suction. The batch stood overnight at room temperature. The pale yellow precipitate was then filtered off with suction, washed with 300 ml of water to neutral pH and dried well. Crude yield: 87.2 g of pale yellow crystals. The crude product was then stirred with 100 ml of acetone, filtered off with suction and dried in vacuo.

Provenance & Evidence