Reactions of [2‐(2‐Naphthyl)phenyl]acetylenes and 2‐(2‐Naphthyl)benzaldehyde O‐Phenyloximes: Synthesis of the Angucycline Tetrangulol and 1,10,12‐Trimethoxy‐8‐methylbenzo[c]phenanthridine

Abstract

The Suzuki–Miyaura coupling reaction between (1,4,5‐trimethoxynaphthalen‐2‐yl)boronic acid and 2‐iodo‐3‐methoxy‐5‐methylbenzaldehyde gave the intermediate 3‐methoxy‐5‐methyl‐2‐(1,4,5‐trimethoxynaphthalen‐2‐yl)benzaldehyde. Conversion of this benzaldehyde into the alkyne 2‐(2‐ethynyl‐6‐methoxy‐4‐methylphenyl)‐1,4,5‐trimethoxynaphthalene was accomplished through a Corey–Fuchs reaction. Exposure of the derived acetylene to a catalytic platinum(II)‐mediated ring closure gave the required tetracyclic aromatic product, 1,7,8,12‐tetramethoxy‐3‐methyltetraphene, which was then converted into tetrangulol. Exposure of the related 3‐methoxy‐5‐methyl‐2‐(1,4,5‐trimethoxynaphthalen‐2‐yl)benzaldehyde O‐phenyloxime to microwave irradiation in an ionic liquid yielded 1,10,12‐trimethoxy‐8‐methylbenzo[c]phenanthridine, instead of the desired natural product phenanthroviridone.