Propargyl bromide → 4-Hydroxy-6-methyl-3-propargylthio-2-pyrone

Reaction equation

[OH:1][C:2]1[CH:7]=[C:6]([CH3:8])[O:5][C:4](=[O:9])[C:3]=1[SH:10].[CH2:11](Br)[C:12]#[CH:13].[Br-].[NH+]1C=CC=CC=1>N1C=CC=CC=1>[OH:1][C:2]1[CH:7]=[C:6]([CH3:8])[O:5][C:4](=[O:9])[C:3]=1[S:10][CH2:13][C:12]#[CH:11]

Participants

Procedure

A solution of 39.5 g. (0.250 mole) of 4-hydroxy-3-mercapto-6-methyl-2-pyrone in 250 ml. of pyridine was cooled to 15°C. in an ice bath. Propargyl bromide (29.7 g., 0.250 mole) was then added in one portion, causing the temperature of the reaction mixture to rise to 53°C. When the temperature began to subside, the flask was placed on the steam bath and heated at 80°C. for one hour, during which pyridinium bromide by-product precipitated. The reaction mixture was then cooled and poured into a mixture of ice and 500 ml. of concentrated hydrochloric acid. After this mixture had been kept cold in an ice bath for one hour, the crystalline product, which formed, was collected on a filter and dried; m.p. 143.5°-146°C., weight 27.2 g. More product was obtained by extraction of the filtrate with methylene chloride, giving a total yield of 41.9 g., (85 percent). Two recrystallizations (Darco) from ethanol afforded the pure 4-hydroxy-6-methyl-3-propargylthio- 2-pyrone as light tan crystals, m.p. 148°-149°C. (dec.).