Atroposelective Synthesis of 2,2′‐Bis(arylamino)‐1,1′‐biaryls by Oxidative Iron(III)‐ and Phosphoric Acid‐Catalyzed C−C Coupling of Diarylamines**

Abstract

We describe an iron‐catalyzed asymmetric oxidative C−C coupling of diarylamines which proceeds at room temperature with air as final oxidant. Using hexadecafluorophthalocyanine‐iron(II) as catalyst in the presence of catalytic amounts of an axially chiral biaryl phosphoric acid, the resulting chiral 2,2′‐diamino‐1,1′‐biaryls are obtained in up to 90 % ee as confirmed by chiral HPLC. A detailed mechanism has been proposed with a radical cation‐chiral phosphate ion pair as key intermediate leading to the observed asymmetric induction.

μ-Oxo-bis[(octacosafluoro-meso-tetraphenylporphyrinato)iron(iii)] – synthesis, crystal structure, and catalytic activity in oxidation reactions

“…In the present study,‡‡Part 153 of “Transition Metals in Organic Synthesis”; for part 152, see: ref. 30. we describe the synthesis, structural characterization, and applications in catalysis of the strongly electron-deficient complex μ - oxo-bis[(octacosafluoro- meso -tetraphenylporphyrinato)iron( iii )] [(FeTPPF 28 ) 2 O] ( 5c ) (Table 1). We focused our efforts on the fluorinated porphyrin ligands, since in addition to the electron-withdrawing effect of the fluorine atoms they improve considerably the solubility of the complexes.…”

“…2). 30 Initial attempts with the unsubstituted meso -tetraphenylporphyrin–iron complex FeTPPCl and the corresponding β-octafluorinated complex 4a in the presence of methanesulfonic acid as additive gave no turnover (Table 2, entries 2 and 3). The perfluorinated complex FeTPPF 28 Cl ( 4c ) gave only traces of the product 7 (entry 4).…”

“…34 Recently, we have shown that oxidation of 10d with FePcF 16 as catalyst in the presence of 10 mol% of the chiral phosphoric acid ( R )- 12 as co-catalyst afforded 11d in 71% yield and 90% ee (Table 5, entry 1). 30 The chiral phosphate counter-ion was believed to direct the asymmetric coupling of the radical cation generated from 10d by an initial single-electron transfer. Using 5c as catalyst in the presence of 20 mol% of ( R )- 12 led to the biaryl compound 11d in 96% ee (Table 5, entry 3).…”

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

“…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).…”

Direct Arylation of C(sp2)–H Bonds in Anilines

“…Scheme 16 Direct ortho-arylation of para-substituted anilines via a rhodium-catalyzed aerobic oxidative homocoupling A similar ortho-selective radical homocoupling of anilines was recently applied to the atroposelective synthesis of 2,2′-bis(arylamino)-1,1′-biaryl derivatives by the Knölker group (Scheme 17). 35 In this case, an iron(III)-perfluoroporphyrin-type complex allows the aerobic oxidative coupling to be performed in a similar manner to that described above, the atroposelectivity being rationalized by the authors through the formation of a chiral ion pair between the chiral phosphate (CPA) and the radical cation iminium intermediate.…”