Single‐Electron‐Transfer‐Initiated Sequential Direct Arylation Reaction of Pyrrole with Aryl Diazonium Salts

Abstract

Direct and sequential arylations of pyrrole with a diazonium salt were initiated by single electron transfer from cobaltocene. The direct arylation reaction of pyrrole was completed within 30 min even at room temperature and the corresponding arylated product was obtained in good yield. The second arylation reaction of monoarylated heteroarenes also proceeded successfully and moderate to good yields of diarylated pyrroles were obtained. A gramscale reaction also proceeded without decreasing the yield of the product.[a] Dr.

Recent Development of Aryl Diazonium Chemistry for the Derivatization of Aromatic Compounds

“…The role of ferrocene in aryl radical formation was confirmed by cyclic voltammetry . Additionally, direct and sequential arylations of pyrrole with aryl diazonium salt can also be initiated by the SET process catalyzed by cobaltocene at room temperature …”

“…70 Additionally, direct and sequential arylations of pyrrole with aryl diazonium salt can also be initiated by the SET process catalyzed by cobaltocene at room temperature. 71 Gomberg−Bachmann arylation of pyridine usually leads to a mixture of regioisomers. Aiming to achieve the regioselective arylation of pyridine, a regioselective radical arylation of 3hydroxypyridine 50 was realized using a stoichiometric amount titanium(III) complex.…”

Strategic Advances in Sequential C-Arylations of Heteroarenes

“…Similarly, Itoh and co-workers adopted a cobaltocene (Cp 2 Co)-catalyzed single electron transfer-initiated Meerwein-type reaction (Scheme ). Cp 2 Co, being a 19 e – complex, acts as an electron donor that stabilizes into an 18 e – system, thus producing aryl radicals.…”

“…Similarly, Itoh and co-workers adopted a cobaltocene (Cp 2 Co)-catalyzed single electron transferinitiated Meerwein-type reaction (Scheme 3). 18 Cp 2 Co, being a 19 e − complex, acts as an electron donor that stabilizes into an 18 e − system, thus producing aryl radicals. Doucet's group reported sequential desulfitative arylation of pyrroles, which was carried out using widely available Ar-SO 2 Cl and was catalyzed by PdCl 2 (MeCN) 2 /Li 2 CO 3 .…”

Design of a Mesoionic Janus-type Dicarbene

“…Thereafter, the viability of complex 4 for the sequential C5arylation of the monoarylated compound 8 to access nonsymmetrical 2,5-diarylpyrroles was tested using bromobenzene (Scheme 3). It should be emphasized that only three sequential 2,5-diarylation reports of N-substituted pyrroles using aryl bromides, 22 benzenesulfonyl chlorides, 32 and aryl diazonium salts 36 as the respective coupling partners are known thus far. The catalytic reaction employing a 0.5 mol % loading of 4 afforded the unsymmetrical product 10 in 64% isolated yield (over two runs), which is a hitherto unknown compound.…”