合成路线1

A further route to benzyl ester (X) is shown in the next scheme: Protection of 2,4,6-trimethylaniline (XI) with Boc2O gave carbamate (XII). Condensation of (XII) with diethyl oxalate in the presence of sec-butyllithium produced the intermediate ketoester (XIII), which was deprotected and cyclized under acidic conditions to yield indole (V). Hydrolysis, followed by alkylation with benzyl bromide as above provided the corresponding benzyl ester (X). An alternative and more direct procedure consisted in the condensation of protected aniline (XII) with dibenzyl oxalate, and then cyclization upon treatment with trifluoroacetic acid. The intermediate indole (X) was N-alkylated with tert-butyl bromoacetate and NaH to give the indole diester (XIV). Subsequent deprotection of the benzyl ester group by hydrogenation over Pd/C gave rise to diacid mono tert-butyl ester (XV). Optionally, the analogous methyl ester (XVII) was prepared by alkylation of indole (X) with methyl bromoacetate, followed by benzyl group hydrogenolysis.