“…[8a] Alternatively, heterocycles may be metallated and then quenched with MeSSMe. Thus, N-methylpyrrole (1 b) was lithiated with nBuLi [10] and the resulting lithium reagent was treated with dimethyl disulfide to afford 1-methyl-2-(methylthio)pyrrole (2 b) in 68 % yield (Scheme 1b). The methylation of heterocyclic thiols constitutes another method.…”
A variety of unsaturated thioethers have been subjected to cross-coupling reactions with functionalized zinc reagents in the presence of a transition-metal catalyst. Three different catalytic systems based on Pd(OAc)(2) or [Ni(acac)(2)] and the ligands S-Phos or DPE-Phos gave the best results. N-Heterocyclic thioethers based on a pyridine, pyrimidine, pyrazine, pyridazine, triazine, benzothiazole, benzoxazole, pyrrole, or quinazoline ring, as well as thiomethylacetylenes, serve as electrophiles in this cross-coupling reaction. Aryl-, heteroaryl-, benzylic, and alkylzinc halides with sensitive functionalities, such as ester, nitrile, or ketone groups react at ambient temperature with unsaturated thioethers using a Ni catalyst. The corresponding Pd-catalyzed reactions require slightly higher temperatures. Large-scale cross-coupling experiments (10-20 mmol) with N-heterocycles are also reported.
“…[8a] Alternatively, heterocycles may be metallated and then quenched with MeSSMe. Thus, N-methylpyrrole (1 b) was lithiated with nBuLi [10] and the resulting lithium reagent was treated with dimethyl disulfide to afford 1-methyl-2-(methylthio)pyrrole (2 b) in 68 % yield (Scheme 1b). The methylation of heterocyclic thiols constitutes another method.…”
A variety of unsaturated thioethers have been subjected to cross-coupling reactions with functionalized zinc reagents in the presence of a transition-metal catalyst. Three different catalytic systems based on Pd(OAc)(2) or [Ni(acac)(2)] and the ligands S-Phos or DPE-Phos gave the best results. N-Heterocyclic thioethers based on a pyridine, pyrimidine, pyrazine, pyridazine, triazine, benzothiazole, benzoxazole, pyrrole, or quinazoline ring, as well as thiomethylacetylenes, serve as electrophiles in this cross-coupling reaction. Aryl-, heteroaryl-, benzylic, and alkylzinc halides with sensitive functionalities, such as ester, nitrile, or ketone groups react at ambient temperature with unsaturated thioethers using a Ni catalyst. The corresponding Pd-catalyzed reactions require slightly higher temperatures. Large-scale cross-coupling experiments (10-20 mmol) with N-heterocycles are also reported.
“…Thus, the reaction of the zinc reagent 2f with the nonaflate 1k provided the quinoline 3k in 88% yield (entry 12). 2-Zincated N -methylpyrrole ( 2g ) obtained from the corresponding lithium reagent and ZnBr 2 underwent a smooth cross-coupling with 3-bromopyridine ( 1f ) at 70 °C leading to β-nicotyrine 3l in 62% yield (entry 13), a natural product with insecticidal activity (Scheme 2). …”
[reaction: see text] The combination of diethyl phosphite and DMAP as ligands for nickel in an 8:1 THF-N-ethylpyrrolidinone (NEP) mixture allows a very efficient cross-coupling reaction to be performed between various functionalized arylzinc halides and aryl bromides, triflates and activated chlorides. The reaction proceeds at 25 degrees C within 1-48 h and requires only 0.05 mol % of the nickel catalyst.
“…Generation of 260 may also be carried out using BuLi at ambient temperature in THF-hexane (2 : 1). This lithiopyrrole will subsequently react readily with a wide variety of electrophiles [398], and may for example also be converted into the 2-alkyl-1-methylpyrroles 261 by treatment with trialkylboranes, followed by addition of iodine or NCS [399,400]. Quenching of 2-lithio-1-methyl-5-noctylpyrrole with N-fluorodibenzenesulfonamide has been used to prepare the labile 2-fluoro-1-methyl-5-n-octylpyrrole [401].…”
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