*2.1. Synthesis of Double Aza-oxa[7]helicene 3*

Recently, Zhang reported a facile acid-mediated synthesis of carbazole in which aniline derivatives react with *p*-benzoquinone to produce 3-hydroxycarbazoles [48]. Combining this approach with our unprecedented electrochemically enabled synthesis of hetero[7]helicenes and dehydro-hetero[7]helicenes [46,47], herein, we achieved the two-step synthesis of double aza-oxa[7]helicenes as depicted in Scheme 1. The acid-mediated annulation of the commercially available substrates; *N1*,*N4*-di(naphthalen-2-yl)benzene-1,4 diamine **1** and *p*-benzoquinone afforded the corresponding bis-3-hydroxy-benzo[c]carbazole **2** in 54% yield via a tandem process of double Michael addition and subsequent double ring closure. Next, a DCM solution of **2**, β-naphthol, and tetrabutylammonium hexafluorophosphate(V) as an electrolyte, was utilized to a constant current of 1.5 mA in an undivided electrolysis cell with platinum electrodes for 3.5 h at room temperature, affording double aza-oxa[7]helicene **3** in 26% yield. The electrochemical sequential synthesis of **3** proceeds through the oxidative hetero-coupling of arenols to produce a diol intermediate that can readily undergo a subsequent dehydrative cyclization to **3**. All compounds showed good chemical and thermal stabilities and no decomposition was observed upon purification on silica column chromatography and heating at 100 ◦C in air.

**Scheme 1.** The synthesis of a double aza-oxa[7]helicenes **3**.
