Synthesis of [7]Helicene Enantiomers and Exploratory Study of Their Conversion into Helically Chiral Iodoarenes and Iodanes

Abstract

The facile and convenient preparation of both enantiomers of a [7]helicene scaffold from inexpensive (l)‐(+)‐tartaric acid and 4‐methylstyrene is described. These helical structures were transformed into bis‐iodinated ether derivatives in order to explore their potential as precursors of novel chiral organoiodane reagents or as iodoarene pre‐catalysts. Promising results were obtained in hydroxylative phenol dearomatization/[4+2] cycloaddition cascade and dearomative spirolactonization reactions with encouraging enantiomeric excesses.

Toward Zigzag‐edged Helical Nanographene Based on [7]Helicene

“…The chemical structure of 1 is unambiguously confirmed by the X‐ray crystallographic analysis, revealing a P ‐[7]helicene based nanographene with rich zigzag periphery. The dihedral angle ( θ IC =20.63°) of compound 1 was smaller than that of 3,16‐dimethoxy‐[7]helicene (48.50°) [13] . The maximum absorption peak of 1 is red shift by 124 nm compared to that of compound 5 due to the intramolecular push‐pull effect which derived from the methoxy and C=O groups.…”

“…The synthetic route towards P ‐[7]helicene‐based nanographene 1 is depicted in Scheme 1. The key building block 4,15‐diiodo‐3,16‐dimethoxybenzo[1,2‐ c : 4,3‐ c′ ]diphenanthrene ( 3 ) was synthesized from 3,16‐dimethoxybenzo[1,2‐ c : 4,3‐ c′ ]diphenanthrene 2 [13] by treatment with N ‐iodosuccinimide under a catalytic amount of silver(I) triflimide in 77% yield. Subsequently, the Suzuki coupling of compound 3 with 2‐formylphenylboronic acid afforded 3,16‐dimethoxybenzo[1,2‐ c : 4,3‐ c′ ]diphenanthrene‐4,15‐diyl)dibenzaldehyde 4 in the yield of 33%.…”

Hypervalent iodine-mediated synthesis and late-stage functionalization of heterocycles

“…Later, Quideau's research group succeeded in constructing helicine-based chiral iodoarene catalyst 316 from inexpensive precursors (L)-(+)-tartaric acid and 4-methylstyrene. 119 This novel chiral catalyst 316 served as catalyst for the dearomative spirolactonization of 309 to afford chiral spirolactones 312 with moderate selectivity. Notably, reaction catalyzed by catalyst 306 and 307 gives (R)-isomer 312.…”

Recent Advances in the Selective Oxidative Dearomatization of Phenols to o-Quinones and o-Quinols with Hypervalent Iodine Reagents

“…21 It is worth noting that when aqueous acetonitrile was used in place of EtOAc, almost exclusive p-quinone was obtained, likely due to competitive intermolecular attack of H 2 O in the para position. While phenol substrates were again limited to those possessing electron-donating groups (37)(38)(39), polycyclic scaffolds could be unsubstituted (40,43) or even possess halogen substituents such as p-Cl (41) and p-Br (42) naphthoquinones, highlighting both the increased reactivity of IBS as well as the more facile oxidation of polycyclic arenols. A notable exception was the use of 3-OMe-naphthol, which instead gave high yields of the p-quinone 44, but this can likely be attributed to observe high levels of background oxidation by Oxone in this highly activated substrate.…”

“…Since these reports, the Quideau lab has continued their efforts in developing novel chiral I(V) scaffolds, including those based on helical chirality (123) 39 and C 2 -symmetrical Salen-type scaffolds (123, 124), 40 and a representative example from their use in phenol dearomatization is shown in Figure 3. It was a common observation across each of these studies that while steric bulk around the iodane center had a positive effect on stereoselectivity, it also led to an erosion of C2 vs. C6 site-selectivity and increasing amounts of o-quinone formation, leading to reduced yields.…”