Thiophene Analogue of Isotanshinone‐II Nucleus: A Novel Approach towards the Synthesis of Phenanthro[4,3‐b]‐thiophene‐4,5‐dione and Phenanthro[3,4‐b]thiophene‐4,5‐dione Derivatives

Abstract

The phenanthraquinone moiety condensed with heteroarene moieties posses various therapeutic activities. In this article, synthesis of some novel thienophenanthraquinones (eg. Phenanthro[4,3‐b]thiophene‐4,5‐dione / phenanthro[3,4‐b]‐thiophene‐4,5‐dione derivatives) is reported using a novel pathway developed by us. 3,4‐Dihydro‐1‐(2‐thienyl)naphthalene‐2‐carbaldehyde derivatives 3 a‐c were aromatized with DDQ to respective 1‐(2‐thienyl)naphthalene‐2‐carbaldehyde derivatives 4 a‐c. Conversion of the CHO functionality to CH2CO2H functionality was achieved in 4 steps to afford 2‐[1‐(2‐thienyl)naphthalene‐2‐yl]acetic acid derivatives 7 a‐c. Intramolecular Friedal‐Crafts acylation of these acids followed by Fremy's salt oxidation of the resulting phenanthro[4,3‐b]thiophene‐4‐ol derivatives 8 a‐c furnished the title compounds 9 a‐c in overall 7 steps. Following a similar route another novel thienophenanthraquinone [10‐methoxyphenanthro[3,4‐b]thiophene‐4,5‐dione 18] has also been synthesized. This synthetic route is very simple with fewer steps and is of good to excellent yields in most of the steps involved.

An Expedite Synthesis of Some Angularly Fused Novel ‘U’‐Shaped Tetracyclic Furophenanthraquinones Simulating ABCD Rings of Isotanshinone‐II

“…Recently we have developed [1] a general and novel synthetic pathway for the preparation of tetracyclic ‘S’‐shaped furophenanthroquinone as well as the tricyclic analog (furonaphthoquinone) simulating ABCD and BCD rings of Tanshinone‐I. The method has great potential for the synthesis of “U‐shaped” furophenanthraquinones as well as their thiophene analogues [21] too. To explore the chemistry of non‐natural furoquinones in this paper we have extended our methodology for synthesis of some novel phenanthro[4,3‐b]furan‐4,5‐dione (the core nucleus of isotanshinone‐II) and their 7‐methyl and 8‐methyl derivatives (the latter being the 3‐demethylisotanshinone‐II) (Figure 1 and Figure 2).…”