Arrested handedness and disordered stacking in crystals of the pre helical molecule 7.8-dioxa[6]helicene

Abstract

Dioxa[6]helicene exhibits arrested chirality in the crystalline state. The asymmetric unit contains 8 different, stacked helical molecules of which two are disordered. The molecules appear in homochiral (3 × 1 × ∞ ) strings. Further analysis indicates that there can be domains of enantiomeric excess and a dipolar structure reminiscent of 1D Ising behaviour.

Synthesis and characterization of semiaromatic polyamides comprising benzofurobenzofuran repeating units

“…Since the dehydration of 3 was impossible to achieve, one might have considered the dehydrogenation of 1 before oxidation, following a bromination-dehydrohalogenation route that had already been used for similar molecules. [37][38][39] However, this approach had already been shown to not work in the specific case of compound 1. 40 On the other hand, dehydrations of alcohols at low temperatures have often been reported to work efficiently using chlorinating agents such as phosphoryl chloride (POCl3) or thionyl chloride (SOCl2) when the compounds are soluble in chlorinated solvents or pyridine.…”

Synthesis of New 7,8-Dioxa[6]helicenes with Triazole Rings as Potential Molecular Tweezers

“…Because of this property, they have been widely applied for different purposes such as organic light-emitting diodes, asymmetric catalyst, liquid crystals, and molecular motors. 1 Because of their structural features that are similar to those of carbocyclic helicenes, heterohelicenes such as oxa [9]helicene and dioxa [6]helicenes have gained much attention for asymmetric synthesis and preparation of optoelectronics. 2 In recent years, dioxa [6]helicenes, especially 7a,14c-dihydro-naphtho[2,1b] [1',2';4,5]furo[3,2] furan derivatives 1, and 8,16-methano-16H-dinaphtho[2,1-d:1',2'-g][1,3]dioxocins 2, 2a-c have found applications in various areas because of their electron-rich inner cavities (Figure 1).…”

“…1 Because of their structural features that are similar to those of carbocyclic helicenes, heterohelicenes such as oxa [9]helicene and dioxa [6]helicenes have gained much attention for asymmetric synthesis and preparation of optoelectronics. 2 In recent years, dioxa [6]helicenes, especially 7a,14c-dihydro-naphtho[2,1b] [1',2';4,5]furo[3,2] furan derivatives 1, and 8,16-methano-16H-dinaphtho[2,1-d:1',2'-g][1,3]dioxocins 2, 2a-c have found applications in various areas because of their electron-rich inner cavities (Figure 1). 3 This type of compounds can be defined as having an inverted 'v' shape geometry.…”

“…Figure 1 'V'-shaped and helical-type dioxa [6]arenes Different from compounds 1 and 2, compounds 3a and 3b, which are dehydrogenated derivatives of 1, have fully aromatic helical structures. It was reported that 3a and 3b have chiral conformations because of their low inversion barriers.…”

“…6,7 Compound 3b crystallizes in the centrosymmetric triclinic space group P1 with the asymmetric unit being composed of two heterochiral (P) and (M) helical crystal packings in the solid state. In order to obtain stable helical molecules based on the dioxa [6]helicene backbone it would be required to achieve regioselective functionalization of the helicene at the sterically most hindered C1 and/or C14 positions. 4 It is known that helicenes…”