Palladium‐Catalyzed Regioselective Direct Arylation of Benzofurazans at the C‐4 Position

Abstract

Abstract. The palladium-catalyzed direct arylation of benzofurazans with aryl bromides to access 4-arylbenzofurazans proceeds in moderate-to-high yields using phosphine-free palladium acetate as the catalyst and potassium acetate as an inexpensive base. A wide variety of (hetero)aryl bromides, including bromopyridine and bromothiophene derivatives has been successfully employed.Palladium-catalyzed one-pot C4,C7-diarylation of benzofurazane was also described using a larger amount of aryl bromide. Moreover, the derivatization of 4-arylbenzofurazans into 4-arylquinaxolines is also reported.

Effective modulation of the photoluminescence properties of 2,1,3-benzothiadiazoles and 2,1,3-benzoselenadiazoles by Pd-catalyzed C–H bond arylations

“…Based on our recent results on palladium-catalyzed direct arylation of benzofurazan using aryl bromides as aryl source, 20 we examined the reactivity of 2,1,3-benzothiadiazole (Table 1). Using our previously reported reaction conditions, namely 1 mol% Pd(OAc) 2 in the presence of KOAc in DMA at 120 ºC, no reaction occurred between 2,1,3-benzothiadiazole and 4bromobenzonitrile (Table 1, entry 1).…”

“…Recently, we disclosed that phosphine-free palladium acetate catalyzes the C-H bond arylation of benzofurazan (Figure 2e). 20 Therefore, we decided to investigate the reactivity of unsubstituted 2,1,3benzothiadiazole and 2,1,3-benzoselenadiazole in palladium-ARTICLE catalyzed C-H bond arylation for the straightforward access to 4-arylated 2,1,3-benzothiadiazoles and 2,1,3benzoselenadiazoles (Figure 2e).…”

“…In comparison with 9, the fluorene-based 2,1,3benzothiadiazole 19 exhibits higher absorptivity within the whole spectrum, due to additional 1 (π-π*) transitions of this πextended system but with no significant shift of the absorption bands. Similarly, replacing the fluorenyl ( 19) by a pyrenyl group (20), gives rise to very intense absorption bands in the UV region, the absorption profile of the benzothiadiazole core being overlapped by the intense and well-resolved absorption bands of the pyrene moiety. The pyrene moiety in 20 induces a small red-shifted of the CT band (∆λ = 15 nm), compared with the fluorene substituent in 19.…”

“…Based on previous experimental and theoretical studies of benzothiadiazole derivatives, the observed spectral changes by incorporation of various aromatic substituents can be interpreted as a modification of the highest-occupied molecular orbital (HOMO) while the lowest-unoccupied molecular orbital (LUMO), centered on the core, stays almost unchanged. 24c In other words, increasing the electron-richness ( 17) and/or extension of the π-system (19,20) destabilize the HOMO energy level resulting in a decrease of the HOMO-LUMO gap with respect to 9. As far as the di-substituted 2,1,3benzothiadiazoles are concerned, compounds 24 bearing two p-chlorophenyl and 26 having with two 3,5bis(trifluoromethyl)aryl groups, exhibit similar absorption profiles with a blue-shift of the charge-transfer band in 24, compare to 26, attributed to the strong electron-withdrawing CF 3 groups (Figure 4).…”

Efficient palladium‐catalyzed C‐S cross‐coupling reaction of benzo‐2,1,3‐thiadiazole at C‐5‐position: A potential class of AChE inhibitors

“…To the best of our knowledge, the majority of functionalization at BTD ring is done at position 4. The reason for it is that position on BTD unit is activated by resonance structure and it allows us to perform easily some reactions, such as S N 2, at this position, and that is why substitution at position 5 remains low explored . Thus, aiming to perform an arylthiol functionalization at position 5, using a low‐cost, and effective methodology, herein we present a palladium‐catalyzed C‐S cross‐coupling methodology (Figure c).…”