The starting ester methyl 4-[2-allyl-6-(2-cyclopentylacetamido)-3-oxo-2H,3H-indazol-1-ylmethyl]-3-methoxybenzoate was itself prepared as follows. Using a similar procedure to that described in Example 42, except starting from methyl 4-[6-(2-cyclopentylacetamido)-3-hydroxyindazol-1-ylmethyl]-3-methoxybenzoate (that is, reaction of this compound with allyl bromide in N,N-dimethylformamide in the presence of sodium hydride), a mixture of methyl 4-[2-allyl-6-(2-cyclopentylacetamido)-3-oxo-2H,3H-indazol-1-ylmethyl]-3-methoxybenzoate, and methyl 4-[3-allyloxy-6-(2-cyclopentylacetamido)indazol-1-ylmethyl]-3-methoxybenzoate was obtained. The mixture of compounds was heated neat at 200° C. for 18 hours, and the product isolated by flash chromatography on silica gel (60 g.), eluting with 1:30:70 v/v/v acetic acid:ethyl acetate:dichloromethane, to give methyl 4-[2-allyl-6-(2-cyclopentylacetamido)-3-oxo-2H,3H-indazol-1-ylmethyl]-3-methoxybenzoate in 81% yield, as an oil with satisfactory NMR spectral data.
