1-Bromo-3-chloropropane → 3-[(3-Chloropropyl)thio]-4-methyl-5-(4-methyl-1,3-oxazol-5-yl)-4H-1,2,4-triazole

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Reaction Conditions

Reaction Steps

This material (498 g, 1 wt) was dissolved in dry tetrahydrofuran (5 vol), under nitrogen, cooled to 0° C. DCC (1.62 wt, 1 eq) was added portionwise followed by HOBt (1.07 wt, 1 eq). The mixture was warmed to 25±2° C. and stirred for 30 min. 4-Methyl-3-thiosemicarbazide (0.83 wt, 1 eq) was then added and the mixture further stirred for 2 h at 25±2° C. The mixture was filtered and the cake was washed with fresh tetrahydrofuran (1 vol) and dried on the filter for a few hours. The cake was suspended in 1 M aqueous NaOH (13 vol) and heated to 70° C. for 30 min. After this time, the mixture was cooled to 25±2° C. and a solid was removed by filtration. The cake was washed with 1 M aqueous NaOH (10 vol). The combined mother liquors were cooled to 0° C. and acidified to ca. pH 5 with HCl (aqueous, 16%; NOTE: keep temperature while adding HCl below +10° C.). The suspended product was isolated by filtration washing with water (2×3 vol). The cake was dried at 40° C. for 18 h in high vacuum to obtain 4-methyl-5-(4-methyl-1,3-oxazol-5-yl)-2,4-dihydro-3H-1,2,4-triazole-3-thione (respectively a tautomeric form thereof; 290 g, 37%). NaOEt (21% solution in EtOH, 2.08 vol, 1.1 eq) was added to EtOH (20 vol) under nitrogen atmosphere. 4-Methyl-5-(4-methyl-1,3-oxazol-5-yl)-2,4-dihydro-3H-1,2,4-triazole-3-thione (respectively a tautomeric form thereof; 290 g, 1 wt) was added in one portion and the resulting mixture stirred at 25±2° C. until a clear solution was obtained. Then 1-bromo-3-chloropropane (0.54 vol, 1.1 eq) was added and the solution stirred at 40° C. for 24 h then cooled to 25° C. After filtration water (20 vol) was added and the ethanolic phase was removed by vacuum distillation (internal temperature ˜40° C.). The mixture was extracted with EtOAc (41 vol). The aqueous layer was removed and the organic phase was evaporated to dryness. Dichloromethane (4 vol) was added. The organic solution is purified through a short silica gel column (18 wt of silica), eluting with EtOAc (200 vol) to give the title compound as a solid foam (267.64 g, 66%).

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