Methyl 1H-Indazole-3-carboxylate
1. A solution of indazole-3-carboxylic acid (100 g) in MeOH (1500 ml) was treated with conc. H2SO4 (100 ml).2. Heated at reflux for 4 h.
3. The mixture was concentrated in vacuo and dissolved in EtOAc (2500 ml).
4. The organic phase was washed with sat. aq. NaHCO3 (1000 ml), H2O (1000 ml), and brine (1000 ml) and dried (MgSO4).
5. Solvent was evaporated under reduced pressure to give 83 g of a white solid.
Methyl 1-Pentyl-1H-indazole-3-carboxylate
1. To a cooled (0 *C) solution of Methyl 1H-Indazole-3-carboxylate (100 g) in THF (1000 ml) was added t-BuOK (70 g).2. The mixture was warmed to rt, stirred for 1 h, and cooled (0 *C), and the appropriate 1-bromopentane (80 ml) was added dropwise.
3. The mixture was warmed to rt and stirred for 48 h, and H2O (1000 mL) was added.
4. The layers were separated, the aqueous layer was extracted with EtOAc (2x500 ml), and the combined organic phases were washed with H2O (3x500 ml) and brine (1000 ml) and dried (MgSO4).
5. Solvent was evaporated under reduced pressure to get (67 g, 77%) as a clear glass-like solid.
1-Pentyl-1H-indazole-3-carboxylic Acid
1. A solution of the appropriate methyl 1-Pentyl-1H-indazole-3-carboxylate (100 g) in MeOH (1000 ml) was treated with 1M aq. NaOH (600 ml) and stirred for 24 h.2. The solvent was reduced in vacuo, and the residue was dissolved in H2O, acidified with 1M aq.HCl, and extracted with EtOAc (2x500 ml).
3. The organic phase was dried (MgSO4), and the solvent was evaporated under reduced pressure to afford the free acid, which was used in the subsequent coupling step without further purification, to yield (68 g, 72%) as a white solid.
ADB-PINACA ((S)-N-(1-Amino-3,3-dimethyl-1-oxobutan-2-yl)-1-pentyl-1H-indazole-3-carboxamide)
1. A solution of 1-Pentyl-1H-indazole-3-carboxylic Acid (100 g) in DMF (1000 ml) was treated with EDC (1 equiv), BtOH (1.5 equiv), DIPEA (180 g), L-tert-leucinamide (86 g) and stirred for 24 h.2. The mixture was partitioned between and H2O (2000 ml) and EtOAc (1000 ml), the layers were separated, and the aqueous layer was extracted with EtOAc (2x1000 ml).
3. The combined organic phases were dried (MgSO4), and the solvent was evaporated under reduced pressure.
4. The crude products were purified by recrystallization to get 92 g of a white solid (yield 63%).
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