SYNTHESIS OF 2-SUBSTITUTED INDOLE WITH HANTZSCH ESTER CATALYZED BY PALLADIUM

摘要

An efficient reductive cyclization of o-nitrobenzyl ketone compounds was achieved by using a Hantzsch 1,4-dihydropyridine ester as a biomimetic reducing agent in the presence of catalytic palladium on carbon. 2-Substituted indoles were obtained in good yields. Investigation of the mechanism suggests that palladium hydride promotes the reduction of nitro group, and acetic acid was beneficial for the loss of water to produce the intended product. This reaction system can not only broaden the use of Hantzsch 1,4-dihydropyridine ester, but it also provides a novel approach for preparing indole compounds.