Conceptually different approach toward biaryl syntheses by photoinduced direct C-H arylation of benzene and thiophene in the presence of t-BuOK is reported. The reaction proceeds through photo- and base-promoted homolytic aromatic substitution. The o-, m- and p- substituted ArI, as well as the electron-donating and electron-withdrawing nature of the substituents were found be good to excellent substrates. Heteroaryl, ArBr, ArCl and double C-H arylation were successfully achieved.

The synthesis of a series of substituted 9H-carbazoles by the photostimulated S(RN)1 substitution reaction with diarylamines as starting substrate was performed. The diarylamines were obtained by two approaches, the Pd-catalyzed reactions (Buchwald-Hartwig) or Cu-catalyzed reactions of 2-haloanilines with aryl halides, or 2-bromoiodobenzene with anilines, with moderate to very good isolated yields (45-89%). Through an intramolecular C-C bond formation of diarylamines by the S(RN)1 mechanism, carbazoles were achieved. These reactions proceeded synthetically in very good to excellent yields (81-99%) in liquid ammonia and DMSO. The reaction of N-(2-bromophenyl)-2-phenylbenzenamine gave 1-phenyl-9H-carbazole (38%) and the isomer 9H-tribenz[b,d,f]azepine (58%). By using this methodology, 9H-carbazoles, substituted 9H-carbazoles, benzocarbazoles, and even 3,3'-bi(9H-carbazole) were obtained by a double S(RN)1 reaction with benzidine.

Previous studies have reported the arylation of unactivated arenes with ArX, base (KOBu or NaOBu), and an organic additive at high temperatures. Recently, we showed that this reaction proceeds in the absence of additives at rt but employs UV-vis light. However, details of mechanisms that can use a photoinduced base-promoted homolytic aromatic substitution reaction (photo-BHAS) have remained elusive until now. This work examines different mechanistic routes of the essential electron-transfer step (ET) of this reaction in order to identify a possible path for the formation of 1-adamantyl radicals from 1-haloadamantanes (initiation step). On the basis of photochemical and photophysical experiments and computational studies, we propose an unprecedented initiation step that could also be applied to other ET reactions performed in DMSO. For the first time, it is reported that dimsyl anion, formed from a strong base and DMSO (solvent), is responsible for inducing the initiation by a photo-BHAS process on alkyl halides.

The synthesis of a series of substituted phenanthridines by photostimulated C-C cyclization of anions from N-(ortho-halobenzyl)arylamines has been found to proceed in very good to excellent yields (79-95%) in liquid ammonia and in DMSO. The N-(ortho-halobenzyl)arylamines are obtained in good to very good isolated yields (44-85%) by nucleophilic substitution of ortho-halobenzylchlorides with different arylamines. The reaction of the anions of a diverse set of N-(ortho-halobenzyl)arylamines was studied, and the methodology was extended to the synthesis of trispheridine, a natural product, in very good yield. In order to explain the regiochemical outcome of these reactions, a theoretical analysis was performed with DFT methods and the B3LYP functional.

Novel approaches for N-and O-desulfonylation under room temperature (rt) and transition-metal-free conditions have been developed. The first methodology involves the transformation of a variety of N-sulfonyl heterocycles and phenyl benzenesulfonates to the corresponding desulfonylated products in good to excellent yields using only KO t Bu in dimethyl sulfoxide (DMSO) at rt. Alternately, a visible light method has been used for deprotection of N-methyl-N-arylsulfonamides with Hantzsch ester (HE) anion serving as the visible-light-absorbing reagent and electron and hydrogen atom donor to promote the desulfonylation reaction. The HE anion can be easily prepared in situ by reaction of the corresponding HE with KO t Bu in DMSO at rt. Both protocols were further explored in terms of synthetic scope as well as mechanistic aspects to rationalize key features of desulfonylation processes. Furthermore, the HE anion induces reductive dehalogenation reaction of aryl halides under visible light irradiation.