合成路线1

Alkylation of N,N-dimethyl-1,3-propanediamine (II) with ethyl bromoacetate (I) afforded the diamino ester (III). Basic hydrolysis of (III) and subsequent nitrosation of the resulting diamino acid (IV) yielded the nitrosamine (V). Cyclization of (V) in hot acetic anhydride as the dehydrating agent gave rise to sydnone (VI). Lithiation of (VI), followed by condensation with aldehyde (VII), produced adduct (VIII) as an inseparable mixture of diastereomers. The hydroxyl group of (VIII) was then protected as the methyl ether (IX) by alkylation with iodomethane and NaH. The azomethyne intermediate, generated by ejection of CO2 from (IX) upon heating in xylene, underwent an intramolecular 1,3-dipolar cycloaddition with the olefin double bond to furnish the indazole derivative (X). Finally, the target compound was obtained by aromatization of (X) under acidic conditions in the presence of platinum catalyst.