Recent advances on the synthesis of flavans, isoflavans, and neoflavans

Abstract

Heterocyclic compounds are the omnipresent structural cores comprising many natural and pharmaceutical products of biological significance. Significantly, heterocyclic compounds are widely distributed in nature, and also have applications in agrochemicals, sanitizers, as dyestuff, as copolymers, etc. Among heterocyles, flavonoids are a class of compounds that are highly interesting and constitute many natural products. In general, all flavanoids contains a basic core of C6‐C3‐C6 of phenyl‐benzopyran backbone. The relative placement of the phenyl group on to the benzopyran core makes further classification into flavanoids, isoflavanoids and neoflavanoids. Flavans (2‐aryl chroman) are subclass of anthoxanthanes exhibits a broad spectrum of biological properties such as anti‐inflammatory, anti‐oxidant, and anti‐malarial properties. Some representative naturally occurring products possessing flavan core are apigenin, luteolin, tangeretin, scutellarein, etc. On the other hand, some of the notable isoflavan‐based natural products are glabridin and (S)‐(−)‐equol. Glabridin is isolated from Licorice roots, which regulates paraoxonase (PON2) levels. While the simple isoflavan (S)‐(−)‐equol, is produced from soy isoflavone intake. Also, natural products such as dalbergichromene, centchroman, and (+)‐myristinin A possess neoflavan (4‐aryl‐3,4‐dihydro‐2H‐chromenes) core structure. Owing to their broad biological and pharmacological properties, synthetic chemists are fascinated in developing new routes toward their synthesis. As a result, a decent number of reports have been established in the literature. Thus, for the past 5 years of time frame, many new methodologies have been witnessed, for the synthesis of various flavan systems. This review emphasizes most of the significant methods on accomplishing flavans, isoflavans and neoflavans and also focused on their applications to the synthesis of relevant natural as well as biologically active products.

Stereoselective Synthesis of Flavonoids: A Brief Overview

“…Isoflavans are a group of isoflavonoids with a variety of biological effects [ 84 ]. Since these compounds belong to a series of molecules where stereogenic centres are confined in 2, 3, and 4 positions, the development of enantioselective pathways to achieve enantiomeric pure moieties at position 3 could unfold stereoselective routes to other similar structures.…”

Recent Advances Towards the Synthesis of Dihydrobenzofurans and Dihydroisobenzofurans

“…[78][79][80] Furthermore, 1,3-dihydroisobenzofuran derivatives are functional building blocks in organic synthesis. [81][82][83][84] They've also been utilized to make phenanthrofurans, [85] isoquinolinones, [86] and chroman spiroketals (Figure 4). [87] Previously, reported reviews were based on synthetic approaches to 2,3-dihydrobenzofurans and natural products bearing the 2,3-dihydrobenzofuran core.…”

“…Also, it acts as anti‐microbial ( 33 ), [76,77] and anti‐depression agents ( 34 ) [78–80] . Furthermore, 1,3‐dihydroisobenzofuran derivatives are functional building blocks in organic synthesis [81–84] . They've also been utilized to make phenanthrofurans, [85] isoquinolinones, [86] and chroman spiroketals (Figure 4).…”

Asymmetric hydrogenation and transfer hydrogenation in the enantioselective synthesis of flavonoids

“…22,23 With advances in asymmetric transition-metal catalysis during the late 1990s and 2000s, enantioselective arylation reactions rapidly became one of the most efficient methods for the asymmetric synthesis of flavonoids. 23–25 Lastly, the enantioselective synthesis of homoisoflavonoids has been recently reviewed by Seo's group. 26…”