反应详情

Tetrahydrofuran (600 ml) was cooled down to −78° C. under argon atmosphere. At this temperature, a 1.7 M solution of tert-butyllithium in n-pentane (200 ml) was added dropwise. After 15 minutes at −78° C., a solution of 22.4 g (106.1 mmol) 5-bromo-3-methyl-1H-indazole in THF (300 ml) was added dropwise at such a rate that the temperature of the solution did not exceed −70° C. The mixture was stirred for 30 minutes before N,N-dimethylformamide (24.5 ml) was added dropwise. After 20 min, the cooling bath was removed, and stirring was continued for 1 h before water (250 ml) was added carefully. The mixture was extracted several times with ethyl acetate (500 ml). The combined organic layers were washed with saturated aqueous sodium chloride solution, dried over sodium sulfate, and concentrated under reduced pressure to yield 18.5 g of crude 3-methyl-1H-indazole-5-carbaldehyde, which was used in the next step without further purification.

1. customdid not exceed −70° C
2. additionwas added dropwise
3. waitAfter 20 min
4. customthe cooling bath was removed
5. waitwas continued for 1 h before water (250 ml)
6. additionwas added carefully
7. extractionThe mixture was extracted several times with ethyl acetate (500 ml)
8. washThe combined organic layers were washed with saturated aqueous sodium chloride solution
9. dry with materialdried over sodium sulfate
10. concentrationconcentrated under reduced pressure