3-Chloro-2-methylaniline → 4-Chloro-1H-indazole

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Reaction Steps

Scheme 3 shows the synthesis of 2-(tetrahydro-2H-pyran-2-yl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2H-indazole 10 starting by cyclization of 3-chloro-2-methylaniline 11 with potassium acetate, acetic anhydride, and isoamyl nitrite to yield 4-chloro-1H-indazole 12. The indazole nitrogen of 4-chloro-1H-indazole 12 was protected as tetrahydropyranyl (THP) with 3,4-dihydro-2H-pyran, and pyridinium p-toluenesulfonate in dichloromethane to yield 4-chloro-2-(tetrahydro-2H-pyran-2-yl)-2H-indazole 13 and a minor amount (about 10%) of the THP regioisomer, 4-chloro-1-(tetrahydro-2H-pyran-2-yl)-1H-indazole. The mixture was reacted with PdCl2(PPh3)2, tricyclohexylphosphine, bis(pinacolato)diboron, and potassium acetate in DMSO and heated to 130° C. for 16 hours to give 10, containing a minor amount (about 10%) of the THP regioisomer, 1-(tetrahydro-2H-pyran-2-yl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-indazole.

Provenance & Evidence