Iron-catalyzed cross-coupling of arylboronic acids with unactivated N-heterocycles and quinones under microwave heating

Abstract

The iron-catalyzed direct arylation of a variety of N-heteroarenes, quinones, and hydroquinones with arylboronic acids is investigated under microwave heating. The reaction proceeds at 70 °C under air using K2S2O8 as an oxidant and FeSO4 as a catalyst. Under microwave heating reaction rates increased by 14 to 115 times. Reaction scope with N-heteroarenes and quinones is comparable to or slightly expanded when compared to previous reports, but the scope of arylboronic acid utility was slightly limited due to previously unobserved arylboronic acid hydroxydeboronation.

Recent advances in iron-catalysed coupling reactions for the construction of the C(sp2)–C(sp2) bond

“…In 2020, Kozak and co-workers reported an iron-catalysed Suzuki cross-coupling reaction of arylboronic acids with unactivated N-heterocycles and quinones under microwave heating. 27 As shown in Scheme 20, the reaction proceeds under air using K 2 S 2 O 8 as the oxidant and FeSO 4 as the catalyst and the reaction time required is only 25 min; however, the literature reported required 12-48 h reaction time. The scope of arylboronic acid utility was slightly limited, and strongly electron-withdrawing groups at the 4-position gave only trace amounts.…”

Blue Light-Emitting Diode-Induced Direct C–H Functionalization of 1,4-Quinones with Aryl and Alkyl Boronic Acids

“…A few of the notable direct C–H functionalizations include Meerwein arylation based on a radical mechanism from potentially explosive diazonium salts, Baran et al .’s Ag-catalyzed arylation/alkylation of 1,4-benzo- and naphthoquinones that utilizes a strong oxidant potassium persulfate (K 2 S 2 O 8 ), and Macgregor and Lee et al .’s Pd-catalyzed direct C–H functionalization of 1,4-benzoquinones with aryl boronic acids (Scheme A). − A few noteworthy arylations/alkylations of benzoquinones with boronic acids include application of iron catalysts and reagents such as Fe­(NO 3 ) 3 , Fe­(II) acetylacetonate, iron oxalate, and FeSO 4 ·7H 2 O in the presence of potassium persulfate (K 2 S 2 O 8 ) as an oxidant under mild conditions or under microwave heating (that reduced the reaction time ∼14- to 115-fold). , A similar arylation/alkylation was achieved with Rh, Mn, and Cd NPs as catalysts. Interestingly, a green protocol was reported where K 2 S 2 O 8 was used as an oxidant in the absence of any base or metal catalysts. , Amid such eclectic protocols, a direct C–H functionalization of 1,4-quinones without any catalyst, base, and oxidant is elusive. At the same time, such a protocol would clearly simplify, expedite, and economize the synthesis of 1,4-quinone-containing targets.…”