合成路线1

Condensation of dichloronitrotoluene (I) with diethyl oxalate in the presence of KOEt afforded phenylpyruvate (II), and subsequent reductive cyclization gave indole-2-carboxylate (VI). Alternatively, condensation of 3,4-dichlorophenyl hydrazine (III) with ethyl pyruvate (IV) provided hydrazone (V). Then, Fischer indole synthesis with p-TsOH in refluxing toluene yielded a mixture of 5,6-dichloroindole (VI) and the corresponding 4,5-dichloroindole. Ester reduction using LiAlH4 in THF afforded alcohol (VII), which was subsequently oxidized to aldehyde (VIII) with MnO2 in Et2O. Condensation of (VIII) with phosphonate (IX) in the presence of NaH provided E-indolylpropenoate (X). Then, the sequence of DIBAH reduction, followed by oxidation of the resulting allyl alcohol (XI) with MnO2 in EtOAc furnished aldehyde (XII).