Iron‐Catalyzed Oxidative C−C and N−N Coupling of Diarylamines and Synthesis of Spiroacridines

Abstract

We describe iron-catalyzed intermolecular oxidative coupling reactions of diarylamines to form substituted 2,2'bis(arylamino)biaryl compounds, tetraarylhydrazines, and 5,6dihydrobenzo[c]cinnolines with the same hexadecafluorinated iron-phthalocyanine catalyst. The mild formation of CÀC or N À N bonds was controlled by the use of acidic or basic additives. In contrast to most iron-catalyzed dehydrogenative coupling reactions, ambient air could be used as the sole oxidant. Moreover, iron(III) chloride hexahydrate promoted a one-pot coupling and subsequent intramolecular dearomative coupling to give 10H-spiro[acridine-9,1'-cyclohexa-2',5'dien-4'-ones].

2,2′‐Bis(arylamino)‐1,1′‐biaryls as Building Blocks for the Synthesis of Dibenzo[d,f][1,3]diazepines, Dibenzo[d,f][1,3]diazepinones, and Dibenzo[c,e][1,2,7]thiadiazepine 6‐Oxides

“…[a] Reaction conditions: A: 3 (1.0 equiv), FePcF 16 (2×0.5 mol%), MsOH (10 mol%), CH 2 Cl 2 , rt, air; B: 3 (1.0 equiv), FePcF 16 (2×2.5 mol%), MsOH (50 mol%), CH 2 Cl 2 , rt, air; C: 3 (1.0 equiv), FePcF 16 (1×1.0 mol%), MsOH (10 mol%), CH 2 Cl 2 , rt, air (1×5.0 mol% FePcF 16 and 50 mol% MsOH for 3 e ); [34a] D: 3 (1.0 equiv), O(FeTPPF 28 ) 2 (1×1.5 mol%), BF 3 ⋅OEt 2 (20 mol%), CH 2 Cl 2 , rt, air; [34c] yields refer to isolated products. [b] Using reaction conditions B, cleavage of the acetal occurred.…”

“…We have an ongoing project directed towards the application of iron compounds as catalysts for convenient oxidative transformations, since iron compounds represent environmentally benign catalysts [30,31] . In this context, we found that the hexadecafluorophthalocyanine–iron(II) complex FePcF 16 , [32,33] which under air is immediately oxidized to μ‐oxo‐bis[(hexadecafluorophthalocyanine)iron(III)] (O[FePcF 16 ] 2 ) (Figure 2), [33f] shows exceptional reactivity as catalyst for the oxidative C−C homocoupling reaction of diarylamines 3 to 2,2′‐bis(arylamino)‐1,1′‐biaryl compounds 4 [34a,b] . The iron‐catalyzed oxidative coupling of the diarylamines 3 a – l using hexadecafluorophthalocyanine–iron(II) (FePcF 16 ) as catalyst and methanesulfonic acid as additive under aerobic conditions [34a] provided the compounds 4 a – l in short reaction times and 51–77 % yield (Table 1; see also: Experimental Section).…”

“…In this context, we found that the hexadecafluorophthalocyanine–iron(II) complex FePcF 16 , [32,33] which under air is immediately oxidized to μ‐oxo‐bis[(hexadecafluorophthalocyanine)iron(III)] (O[FePcF 16 ] 2 ) (Figure 2), [33f] shows exceptional reactivity as catalyst for the oxidative C−C homocoupling reaction of diarylamines 3 to 2,2′‐bis(arylamino)‐1,1′‐biaryl compounds 4 [34a,b] . The iron‐catalyzed oxidative coupling of the diarylamines 3 a – l using hexadecafluorophthalocyanine–iron(II) (FePcF 16 ) as catalyst and methanesulfonic acid as additive under aerobic conditions [34a] provided the compounds 4 a – l in short reaction times and 51–77 % yield (Table 1; see also: Experimental Section). A careful fine‐tuning of our original procedure (reaction conditions C) [34a] led to a protocol affording increased yields for many of the coupling products by addition of the iron catalyst (FePcF 16 ) in two portions (reaction conditions A and B) (Table 1, entries 3, 6, and 8–13).…”

“…The iron‐catalyzed oxidative coupling of the diarylamines 3 a – l using hexadecafluorophthalocyanine–iron(II) (FePcF 16 ) as catalyst and methanesulfonic acid as additive under aerobic conditions [34a] provided the compounds 4 a – l in short reaction times and 51–77 % yield (Table 1; see also: Experimental Section). A careful fine‐tuning of our original procedure (reaction conditions C) [34a] led to a protocol affording increased yields for many of the coupling products by addition of the iron catalyst (FePcF 16 ) in two portions (reaction conditions A and B) (Table 1, entries 3, 6, and 8–13). It is important to note, that all of the iron‐catalyzed C−C coupling reactions using reaction conditions A and B were performed on gram scale using up to 2.5 g of starting material 3 .…”

Straightforward Access to 3,4‐Dihydro‐2H‐1,2,4‐benzothiadiazine 1,1‐dioxides and Quinazolines via Iron‐Catalyzed Aerobic Oxidative Condensation of Amines

“…For these transformations, air or molecular oxygen are ideal oxidants because they are abundant, cheap, and generates at best only water as the by‐product. In recent years, iron‐catalyzed aerobic oxidative reactions through C−H functionalization have received considerable attention owing to their efficiencies, low cost, and environmentally friendly features, and have become a powerful tool for the construction of synthetically valuable heterocycles, such as indolizines, isoxazoles, imidazoles, spiroacridines, quinazolines, 1,3‐benzazoles, and pyridines . Our interest in aerobic oxidation reactions,, prompted us to study iron‐catalyzed oxidative annulation reactions that could employ air (O 2 ) as an oxidant, and we describe here a straightforward method for the construction of 3,4‐dihydro‐2 H ‐1,2,4‐benzothiadiazine 1,1‐dioxides and quinazolines via iron‐catalyzed oxidative condensation of benzylamines with 2‐aminobenzenesulfonamide/2‐aminobenzylamines (Scheme , eq.…”