Synthesis of bisindolyl diphenylene from its ketone derivatives by infrared irradiation supported on a natural clay

We examined the near-infrared (NIR) light-induced assembly efficiency to obtain light-sensitive 3,3′-(9H-fluorene-9,9-diyl) bis(1H-indole) derivatives using natural clay as metal-free Brønsted–Löwry catalyst (bentonitic Tonsil–Actisil FF (TAFF) clay) and an adduct of aluminum (III) chloride with 9-fluorenone. Their mixtures in solventless and aprotic solvent conditions were also explored. Among all the modified reactions tested, the combined effects of TAFF natural clay with NIR light, specifically in the λ 1.1 µm spectral region, result especially efficient to achieve the formation of C–Cπ bonds between π-excessive azaheteroaromatic reagents and functionalized polycyclic aromatic hydrocarbon to give the title compound in good yields within reasonable reaction times. The reaction coordinate was obtained using quantum chemical calculations. All the reactants, products, intermediates, and transition states were obtained for four systems. Natural orbital analysis allowed us to rationalize the transformations. Overall, this approach represents a greener and equally efficient alternative for conducting C–Cπ bond construction reactions in organic chemistry, and it is especially useful for protecting photosensitive compounds from abrupt decomposition.