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66 Science of Synthesis 1.1 Organometallic Complexes of Nickel The slurry was then warmed to rt and stirred for 30 min. Additional THF (1 mL) was added to facilitate stirring. The alkene (288 mg, 0.98 mmol) and [Ni(acac) 2](1; 18mg, 0.07 mmol) were added sequentially as solids, and the resulting dark soln was heated immediately to 49–50 8C for 2–3 h. The reaction was monitored by HPLC and upon completion was quenched with aq 1 M NH 4Cl. The resulting mixture was partitioned with EtOAc and the organic layer was dried (Na 2SO 4) and concentrated under reduced pressure. The residue was chromatographed to afford 73; yield: 348mg (93%). 1-[(1R*,2R*,3R*)-2-Acetyl-3-phenylcyclohexyl]acetone [(1R*,2R*,3R*)-75]: [131] A1.59Mt-BuLi soln in pentane (1.7 mL, 2.7 mmol) was added dropwise to a soln of PhI (0.273 g, 0.150 mL, 1.34 mmol) in THF (6 mL) at –788C. After stirring for 30 min at –788C the yellow mixture was allowed to warm to 08C, and 1.0 M ZnCl 2 in Et 2O (0.90 mL, 0.90 mmol) was added dropwise by syringe. After 1 h, the resulting mixture and a soln of [Ni(cod) 2](2; 5 mg, 0.018mmol) in THF (2 mL) were simultaneously transferred by cannula to a soln of 74 (72 mg, 0.40 mmol) in THF (1 mL) at 08C. After stirring at 0 8C for 2 h the brown mixture was quenched with sat. NaHCO 3 (25 mL), extracted with EtOAc (3 ” 25 mL), dried (Na 2SO 4), filtered, and concentrated. Flash chromatography (silica gel, hexanes/EtOAc 5:1) afforded, in order of elution, (1S*,2R*,3R*)-75 as a pale yellow oil and (1R*,2R*,3R*)-75 as a white solid; both were homogeneous as judged by TLC analysis; yields: (1S*,2R*,3R*)-75, 12 mg (12%); (1R*,2R*,3R*)-75, 60 mg (58%). 1.1.4.2.3 Variation3: Organozirconiums The conjugate addition of organozirconium reagents in the presence of catalytic amounts of bis(acetylacetonato)nickel(II) (1) has received a modest level of attention (Scheme 61). [139–142] The alkenylzirconium 76 may be generated in situ by treatment of alkynes with chloro(hydrido)zirconocene. It has perhaps received less attention than might be expected owing to the popularity of the copper-catalyzed conjugate addition of organozirconiums. [143] Scheme 61 Conjugate Addition of Alkenylzirconiums [140–143] ZrCp2Cl(H) H Cp2ClZr H H 76 O Ni(acac)2 1 3-[(E)-3,3-Dimethylbut-1-enyl]cyclohexanone (77): [139] Complex 76 (1.924 g, 5.67 mmol) and cyclohex-2-enone (0.623 g, 6.48mmol) were dissolved in THF (30 mL) and cooled to 08C. [Ni(acac) 2](1; 0.151 g, 0.59 mmol) was added and the mixture was stirred at 0 8C for 6.5 h. The mixture was quenched with NH 4Cl and extracted with Et 2O. Compound 77 was isolated by distillation of the Et 2O solvent, followed by preparative liquid chromatography of the resulting oil. Distillation of solvent from the fraction containing the product gave 77; yield: 0.744 g (73%). 73% O 77
1.1.4 Nickel–Alkene Complexes 67 1.1.4.2.4 Variation4: Direct Conjugate Addition of Alkyl Halides In contrast to each of the above variations, alkyl iodides may also be utilized directly in nickel-catalyzed conjugate additions. The mechanism of this class of reactions is not well defined; however, the related stoichiometric coupling of enals (e.g., 79) with alkyl halides (e.g., 78) has been demonstrated to proceed through nickel–ð-allyl intermediates. [38] The most widely used variant employs nickel(II) chloride hexahydrate in either catalytic or stoichiometric quantities with activated zinc as a stoichiometric reductant (Scheme 62). [144–148] The organic halide may be either sp 2 or sp 3 hybridized, and alkene geometry in the final product (e.g., 80) is maintained with alkenyl iodides. Scheme 62 Conjugate Addition of Alkyl Iodides [145] TBDMSO O O S H H OTBDMS 78 H I + NiCl2 6H2O Zn, py 73% CO2Et 79 TBDMSO O O S H H OTBDMS 80 H CO 2Et The intramolecular conjugate addition of alkenyl iodides (e.g., 81) in the presence of a sixto sevenfold excess of bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2) has been reported (Scheme 63). [149,150] A large excess of nickel is required owing to its dual role of conjugate-addition catalyst and nitroaromatic reducing agent. This provides an effective route to (€)-19,20-didehydrotubifoline (80). Alkenyl iodides also add to nonactivated double bonds. [151,152] Scheme 63 Conjugate Addition of Alkenyl Iodides [149,150] O O2N N 81 I Ni(cod) 2 2 Et3N, LiCN 40% N N 82 H for references see p 79
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Science of Synthesis Houben-Weyl Me
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4.4.27 Product Subclass 27: Æ-Halo
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4.4.27 Æ-Haloalkylsilanes 147 Sche
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4.4.27 Æ-Haloalkylsilanes 149 dros
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4.4.27 Æ-Haloalkylsilanes 151 4.4.
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4.4.27 Æ-Haloalkylsilanes 153 In g
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4.4.27 Æ-Haloalkylsilanes 155 4.4.
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4.4.27 Æ-Haloalkylsilanes 157 Æ-H
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References 159 References [1] Haman
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References 161 [93] Bruno, J. W.; S
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166 Biographical Sketches Alan Spiv
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168 5.1.22 Product Subclass 22: Ary
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170 Science of Synthesis 5.1 German
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176 References [43] Eaborn, C.; Var
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178 Abbreviations Chemical (cont.)
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180 Abbreviations Ligands (cont.) 2
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182 Abbreviations General (cont.) q
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