Highly Distorted Multiple Helicenes: Syntheses, Structural Analyses, and Properties

Abstract

A series of hexapole helicenes (HHs) and nonuple helicenes (NHs) were prepared from 1,3,5-tris[2-(arylethynyl)phenyl]benzene through two steps, namely, iodocyclization and subsequent palladium-catalyzed annulation with ortho-bromoaryl carboxylic acids. The crucial advantages of this synthetic method are the facile introduction of substituents, high regioselectivity, and efficient backbone extension. Three-dimensional structures of three C 1 -symmetric HHs and one C 3 -symmetric NH were elucidated using X-ray crystallography. Unlike most conventional multiple helicenes, the HHs and NHs investigated herein possess a unique structural feature where some double helical moieties share a terminal naphthalene unit. Chiral resolution of a HH and an NH was successfully achieved, and the enantiomerization barrier (ΔH ‡ ) of the HH was experimentally determined to be 31.2 kcal/mol. A straightforward method for predicting the most stable diastereomer was developed based on density functional theory calculations and structural considerations. It was found that the relative potential energies (ΔH r s) of all diastereomers for two HHs and one NH can be obtained using minimal computational effort to analyze the types, helical configurations, numbers, and ΔH (MP−MM) s [= H(M,P/P,M) − H(M,M/P,P)] of the double helicenyl fragments.

All Carbon Helicenes and π‐Extended Helicene Derivatives

“…In 2023, Wu and colleagues generated a series of hexapole helicenes (HHs) 101-103 and nonuple helicenes (NHs) 104 through two-step reactions with yields as 25-50 % (Figure 55). [60] 101-n Bu-104-n Bu showed absorption peak at 385, 388, 399 or 418 nm, respectively. The FL emission peak and Φ F values are detected as below: 101-n Bu, λ em = 507 nm (Φ F = 5 %); 102-n Bu, λ em = 506 nm (Φ F = 6 %); 103-n Bu, λ em = 513 nm (Φ F = 6 % ); and 104-n Bu, λ em = 536 nm (Φ F = 3 %).…”

X-ray and Optical Circular Dichroism as Local and Global Ultrafast Chiral Probes of [12]Helicene Racemization

“…Helicene chemistry is a rapidly growing field − with applications to asymmetric catalysis, nonlinear optics, spin filters, switches and sensors, and the design of molecular machines . They can be synthesized with different sizes and are usually referred to as [ n ]­helicenes, where n denotes the number of benzene rings.…”

Oxidation of a triple carbo[5]helicene with hypervalent iodine

“…Over the past ten years, a plethora of pristine multihelicene hydrocarbons with increasing molecular contortion and diverse photophysical and chiroptical properties have been reported. 32–43…”

“…Over the past ten years, a plethora of pristine multihelicene hydrocarbons with increasing molecular contortion and diverse photophysical and chiroptical properties have been reported. [32][33][34][35][36][37][38][39][40][41][42][43] Despite the bloom of multihelicenes in contemporaneous organic synthesis, there have been no successful attempts reported for their functionalization. Recently, some regioselective acyloxylation reactions of polycyclic aromatic hydrocarbons (PAH) with hypervalent iodine compounds were reported.…”