Heterohelicenes through 1,3-Dipolar Cycloaddition of Sydnones with Arynes: Synthesis, Origins of Selectivity, and Application to pH-Triggered Chiroptical Switch with CPL Sign Reversal

Abstract

Regioselective access to heterohelicenes through the 1,3-dipolar cycloaddition of sydnones with arynes is described. Novel access to sydnones and poly(hetero)aromatic aryne precursors allowed the introduction of chemical diversity over multiple positions of the helical scaffolds. The origins of the unconventional regioselectivity during the cycloaddition steps was systematically investigated using density functional theory (DFT) calculations, unveiling the key features that control this reactivity, namely, face-to-face (π···π) or edge-to-face (C–H···π) interactions, primary orbital interactions and distortion from coplanarity in the transition structures (TSs) of the transformation. From the library of 24 derivatives synthesized, a pyridyl containing derivative displayed reversible, red-shifted, pH-triggered chiroptical switching properties, with CPL-sign reversal. It is found that protonation of the helicene causes a change of the angle between the electric and magnetic dipole moments related to the S 1 → S 0 transition, resulting in this rare case of reversible CPL sign inversion upon application of an external stimulus.

Mutual Monomer Orientation To Bias the Supramolecular Polymerization of [6]Helicenes and the Resulting Circularly Polarized Light and Spin Filtering Properties

“…For comparison, maximum absorption dissymmetry factors g abs of 3.2 × 10 –3 and 4 × 10 –3 in CHCl 3 and MCH were obtained for ( P )-2 at 318 and 324 nm, respectively (see Figure S10b). To our knowledge, this is the first observation of CPL sign inversion upon assembly in helicenes. ,, The sign of these low-energy ECD active bands in helicene derivatives is known to be highly substituent-sensitive and we now demonstrate that it is also impacted by the self-assembly, while the inherent chirality of the helical core is not changed.…”

“…Bis-ethynyl-[6]­helicenes 1 and 2 exhibit CPL activity generated at the molecular level and with luminescence dissymmetry factors depending on the substitution pattern. Notably, the supramolecular polymerization of 2 allows one to bias the CPL sign; it becomes opposite in the aggregated state compared to the monomeric one (Figure c) . In addition, we demonstrate very efficient spin filtering for the electrons transmitted through the supramolecular layer.…”

Stereomutation and chiroptical bias in the kinetically controlled supramolecular polymerization of cyano-luminogens

“…The intertwining effect responsible for the formation of the AggII species changes the CPL sign. This CPL sign inversion, well documented for molecular species, 22 is rarely observed for supramolecular polymers. 23 …”

Selective chlorination of iminosydnones for fast release of amide, sulfonamide and urea-containing drugs

“…As the cycloaddition step is rate-determining and irreversible in similar systems, we compared the corresponding [3+2] TSs for the two systems. 26 The Δ G ‡ water for the chlorinated iminosydnone mIS2 (20.5 kcal mol −1 ) was found to be significantly lower than the one for mIS1 (23.0 kcal mol −1 ). This free energy difference of 2.5 kcal mol −1 results into an almost 100-fold increase in rate at room temperature due to chlorination, which is in line with the experimentally-observed rate enhancement.…”