Regiospecific 1,4-addition with Grignard-derived mixed triorganozincate reagents

Fused Systems Based on 2‐Aminopyrimidines: Synthesis Combining Deprotolithiation‐in situ Zincation with N‐Arylation Reactions and Biological Properties

“…Studies have shown that it is possible to employ species such as Zn(TMP) 2 and ZnCl 2 · 2LiCl to intercept polar arylmetals. Within this study, we chose ZnCl 2 · N , N , N′ , N′ ‐tetramethylethylenediamine (TMEDA) as in situ trap to attempt deprotolithiation followed by “ trans ‐metal trapping” and iodolysis from various diaryl ketones (Table ).…”

From Quinoxaline, Pyrido[2,3-b]pyrazine and Pyrido[3,4-b]pyrazine to Pyrazino-Fused Carbazoles and Carbolines

“…To a solution of 2,2,6,6-tetramethylpiperidine (0.51 mL, 3.0 mmol) in THF (3 mL) at 0 °C were successively added BuLi (about 1.6 M hexanes solution, 3.0 mmol) and, 15 min later, ZnCl 2 ·TMEDA [53] (0.25 g, 1.0 mmol). After 15 min at 0 °C, the pyrazine (2.0 mmol) was introduced, and the mixture was stirred for 2 h at rt before addition of I 2 (0.76 g, 3.0 mmol) in THF (3 mL) at 0 °C.…”

“…To a stirred mixture of 2,3-diphenyl pyrido[2,3- b ]pyrazine ( 2a , 0.28 g, 1.0 mmol) and ZnCl 2 · TMEDA [53] (0.26 g, 1.0 mmol) in THF (1 mL) at −20 °C was added dropwise a solution of LiTMP (prepared by adding BuLi (about 1.6 M hexanes solution, 1.2 mmol) to a stirred, cooled (−20 °C) solution of 2,2,6,6-tetramethylpiperidine (0.24 mL, 1.2 mmol) in THF (2 mL) and stirring for 15 min) cooled at −20 °C. After 30 min at −20 °C, trichloroisocyanuric acid (0.30 g, 1.3 mmol) was introduced (CAUTION: dissolution of trichloroisocyanuric acid in THF at a temperature above 0 °C produces intense heat), and the mixture was stirred at this temperature for 1 h before addition of water (5 mL) and extraction with EtOAc (3 × 20 mL).…”

Expanding Mg–Zn Hybrid Chemistry: Inorganic Salt Effects in Addition Reactions of Organozinc Reagents to Trifluoroacetophenone and the Implications for a Synergistic Lithium–Magnesium–Zinc Activation

“…After 24 h, a crop of colourless crystals of 3 was obtained (0.493 g, 33 %). 1 26.57 (CH 2 (THF)), 13.11 (CH 3 (ZnÀEt)), 0.98 ppm (CH 2 (ZnÀEt)). 2 MgA C H T U N G T R E N N U N G (m-Cl) 3 ZntBu} 2 ] (4): ZnCl 2 (0.680 g, 5 mmol) was added to a solution of tBuMgCl (5 mL, 1 m solution in THF, 5 mmol) in toluene (45 mL) and the resulting suspension was stirred at room temperature for 20 h. The solid was removed by filtration, the filtrate slowly concentrated in vacuo and left to stand at room temperature.…”

“…X-ray crystallographic and NMR spectroscopic studies revealed them to be a mixture of the two expected monometallic products of a classical metathesis reaction, namely, TMEDA-solvated alkylzinc chloride [(tmeda)Zn(Et)Cl] [24] and the magnesium chloride THF solvate [MgCl 2 A C H T U N G T R E N N U N G (thf) 4 ] (Scheme 2), showing that the presence of TMEDA inhibits the formation of mixed magnesium-zinc species (not only metathesis intermediate 3, but also the insoluble homoleptic species 2); this illustrates the major role that coordinating solvents can play in bimetallic chemistry. [25,26] The bimetallic constitution of magnesium zincates 3-6 was established by X-ray crystallographic studies ( Figure 1 and the Supporting Information). Contact ion-pair structures 3-6 display a new structural motif in magnesium-zinc mixed-metal chemistry, [27] featuring dimeric arrangements that comprise two metal-chloride-connected {(thf) 2 MgCl 3 ZnR} units.…”