The regioselective access to hetero-helicenes through 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 which 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 S1 → S0 transition, resulting in this rare case of reversible CPL sign inversion upon application of an external stimulus.

中文翻译：

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通过Sydnones与Arynes的1，3-偶极环加成反应合成杂螺旋：合成，选择性的起源和pH触发CPL符号反转的Chiropical开关的应用。

描述了通过sydnones与芳烃的1，3-偶极环加成反应对异戊烯的区域选择性进入。对sydnones和聚（杂）芳族芳烃芳烃前体的新颖访问允许在螺旋支架的多个位置上引入化学多样性。使用密度泛函理论（DFT）计算系统地研究了环加成步骤中非常规区域选择性的起源，揭示了控制该反应性的关键特征，即面对面（π…π）或边对面（CH） …π）相互作用，一次轨道相互作用以及转换的过渡结构（TS）中的共面性引起的畸变。从合成的24种衍生物库中，含吡啶基的衍生物表现出可逆的，红移的，pH触发的手性转换特性，CPL签名反转。发现螺旋烯的质子化导致与S1→S0跃迁相关的电偶极矩和磁偶极矩之间的角度发生变化，导致这种罕见的情况是在施加外部刺激时可逆的CPL符号反转。