Synthesis of Naphtho[2,3-b]indolizine-6,11-dione Derivatives by Iodine Oxidation of 2-Alkyl-1,4-naphthoquinones in the Presence of Substituted Pyridines

Iodine oxidation of 2-alkyl-1,4-naphthoquinones (1) in the presence of substituted pyridines (2) afforded naphtho[2,3-b]indolizine-6,11-dione derivatives (3). Other oxidant systems (MnO2/I- or Fe(ClO4)(3))/I-2) can be used and 2-alkylbenzoquinones reacted in lower yield. Iodination of 3 by I, and dibenzoyl peroxide occurred selectively at position 12.