Synthesis of 3-arylpyrroles and 3-pyrrolylacetylenes by palladium-catalyzed coupling reactions

Scope of the Suzuki−Miyaura Cross-Coupling Reactions of Potassium Heteroaryltrifluoroborates

“…Several conditions for the crosscoupling of pyrroleboronic acid derivatives have been reported in the literature 4a–b,5,25. The relatively limited number of citations might be attributed to difficulties associated with protodeboronation, as well as the propensity of the boronic acids to homocouple 3.…”

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…Stille reactions of 1-triisopropylsilyl-3-(tributylstannyl)pyrrole with suitable aryl halides constitute an alternative route to pyrroles of type 369, whereas palladium-catalyzed coupling of 1-triisopropylsilyl-3-iodopyrrole with terminal acetylenes gives high yields of the corresponding 3-ethynylpyrroles. The TIPS group in all products may be removed efficiently by treatment with Bu 4 NF [418]. In connection with studies on Suzuki couplings involving ethyl 4-bromopyrrole-2-carboxylate, a competing dehalogenation of the halopyrrole was observed.…”

“…Subsequent treatment of the so-obtained 3-lithiopyrrole 278 with suitable electrophiles, followed by desilylation with TBAF gives the corresponding 3-substitued pyrroles 279 via the 1-TIPS derivatives 280 [242]. Intermediate 278 may also be generated by lithiation of 3-iodo-1-(triisopropylsilyl)pyrrole (164), and converted into, for example, the boronic acid 281 or the stannyl derivative 282, which are useful substrates in palladium-catalyzed coupling reactions (Section 4.5.11) [418]. Similar Conversely, lithiations involving pyrroles having a trimethyl or triethylsilyl groups at the nitrogen are more difficult to control in terms of regioselectivity, and are under certain conditions further complicated by migration of the silyl groups [420].…”

Palladium‐Catalysed Cross‐Coupling and Related Reactions Involving Pyrroles

“…It took another thirteen years before Bailey demonstrated89 that N ‐methyl‐C2‐(tri‐ n ‐butylstannyl)pyrrole would engage in true Type II Stille cross‐coupling reactions with iodobenzene to form N ‐methyl‐C2‐phenylpyrrole which was obtained in 54 % yield. With the advent of various effective protocols for the formation of C2‐(tri‐ n ‐butylstannyl)pyrroles31,90–95 and the corresponding C3‐isomers,77,95 the title couplings have enjoyed widespread use not least because of the capacity they offer to prepare heavily substituted pyrroles96,97 and/or products where the fragment attached to the pyrrole is itself heavily substituted 98,99. The cross‐coupling of the C2‐stannylated pyrrole 88 with bromobenzene ( 89 ), so as to provide the tetrasubstituted pyrrole 90 (Scheme ), is illustrative 96…”