A two-step synthesis sequence furnishes quadruply annulated borepins in high yields. The first step involves a nucleophilic substitution reaction between aryl-BFK salts (aryl = mesityl, phenyl) and lithiated bromonapthalene derivatives LiNaph (HNaph = 8-bromonaphthalene (a), 5-bromoacenaphthene (b), 5-bromoacenaphthylene (c)). In the second step, the resulting heteroleptic triarylboranes aryl-B(Naph) (3a-c) are subjected to an intramolecular Ni-mediated Yamamoto reaction to close the seven-membered rings and create the borepins 4a-c. Only in the case of 3b is the Yamamoto reaction accompanied by a C-H activation reaction furnishing the 7-hydro-7-borabenzo[de]anthracene derivative 5. The product ratio 4b/5 can be influenced by control of the local Ni(0) concentration. The borepins 4a-c are benchtop stable and highly soluble even in hexane. Compounds 4a-c undergo reversible one-electron reduction; 4c is also able to accept a second electron in a reversible manner and already at moderate potential values (E = -1.49 V and -1.84 V (vs FcH/FcH)). 4a, 4b, and 5 show photoluminescence in the blue-green region of the spectrum, while 4c is nonfluorescent, which is likely attributable to an intramolecular charge-transfer transition.

The high-yield synthesis of a boron-doped [4]helicene was achieved through a Ni-mediated Yamamoto C-C-coupling reaction; the moderate distortion of the molecular scaffold confers excellent solubility to the air- and water-stable green luminophore.

Depending on the solvent, a brominated arylborane gave the multiple helicene B2-TBPA (pyridine) or the oxadiborepin ODBE (THF) after intramolecular Yamamoto coupling.

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