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

Regioselective access to heterohelicenes through the 1,3-dipolar cycloaddition of sydnones with arynes is described. Novel and poly(hetero)aromatic aryne precursors allowed introduction chemical diversity over multiple positions helical scaffolds. The origins unconventional regioselectivity during steps was systematically investigated using density functional theory (DFT) calculations, unveiling key features that control this reactivity, namely, face-to-face (?···?) or edge-to-face (C–H···?) interactions, primary orbital interactions distortion from coplanarity in transition structures (TSs) transformation. From library 24 derivatives synthesized, a pyridyl containing derivative displayed reversible, red-shifted, pH-triggered chiroptical switching properties, CPL-sign reversal. It found protonation helicene causes change angle between electric magnetic dipole moments related S1 ? S0 transition, resulting rare case reversible CPL sign inversion upon application an external stimulus.