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150 Science of Synthesis 4.4 Silicon Compounds of Product Subclass 27) is also produced (Scheme 4). The reaction of (trimethylsilyl)methyl trifluoromethanesulfonate with sodium iodide is a good method for the synthesis of (iodomethyl)trimethylsilane. [32] A siloxy group has been used as the leaving group in the synthesis of 9-chloro-3-methoxy-9-(trimethylsilyl)fluorene derivatives. [33] Æ-Alkoxymethylsilanes can be transformed into Æ-bromomethyl- and Æ-iodomethylsilanes by the action of triphenylphosphine/bromine and potassium iodide/phosphoric acid, respectively. [34] A more widely used, and related, reaction involves the ring opening of Æ,â-epoxysilanes (see Section 4.4.29) by halide. In this way, Æ-halo-â-hydroxyalkylsilanes are obtained with high regioselectivity by treatment of the epoxide with hydrochloric, [35] hydrobromic, [36] and hydriodic acids (e.g., 17 fi 18) [37] or tetrafluorosilane/water/diethylisopropylamine. [38] The silyl group accelerates the substitution at the Æ-position, even when it is more sterically hindered than the â-position. Scheme 4 Æ-Haloalkylsilanes by Nucleophilic Substitution of a Hydroxy-Derived Leaving Group and Ring Opening of an Æ,â-Epoxysilane by Halide Ion [31,37] Me3Si OTs 14 17 SiMe3 O KF, (HOCH 2CH 2) 2O aq HI 70% 18 Me3Si F + Me3Si F 15 38% 16 10% SiMe3 4.4.27.2.1 Variation 1: Substitution with Chloride Using Thionyl Chloride Early examples of the substitution of Æ-hydroxysilanes with chloride employ thionyl chloride as the reagent. [39] The transformation is achieved simply by mixing the alcohol with thionyl chloride in diethyl ether (19 fi 20, Scheme 5). A benzylsilyl group is not cleaved by the hydrochloric acid produced under these conditions. The reaction has not seen many applications, probably because the yields are not generally high. This has prompted the development of other methods (Sections 4.4.27.2.2 and 4.4.27.2.3). Scheme 5 Æ-Chloroalkylsilanes from Æ-Hydroxyalkylsilanes and Thionyl Chloride [39] OH 19 SiMe3 SOCl2, Et2O, 0 oC to rt 78% (1-Chloropropyl)trimethylsilane (20); Typical Procedure: [39] (1-Hydroxypropyl)trimethylsilane (19; 0.75 g, 5.8 mmol) in dry Et 2O (5 mL) was added dropwise at 0 8C to a stirred soln of SOCl 2 (0.76 g, 6.4 mmol) in dry Et 2O (5 mL). The resulting soln was stirred at 08C for 20 min and at 258C for a further 20 min and then heated under reflux for 1 h. Evaporation produced the Æ-chloropropylsilane 20 as a crude light brown oil; yield: 0.68 g (78%). I OH Cl 20 SiMe3
4.4.27 Æ-Haloalkylsilanes 151 4.4.27.2.2 Variation 2: Chlorination of Æ-Hydroxyalkylsilanes with Triphenylphosphine and Carbon Tetrachloride Significant improvements to the method were accomplished by Barrett and co-workers. They found that conversion of Æ-hydroxyalkylsilanes 21 {prepared by the addition of [(dimethyl)(phenyl)silyl]lithium to aldehydes} [40] into the Æ-chloroalkylsilanes 22 is effected by reaction with carbon tetrachloride and triphenylphosphine without complication (Scheme 6). The Grignard reagent derived from 22 proved to be excellent for the synthesis of Æ-ketosilanes, used in the synthesis of alkenes via the Peterson reaction (see Applications of Product Subclass 27). The reaction and subsequent purification of 22 is not complicated by competing Brook rearrangement. Æ-Bromoalkylsilanes can be prepared in a similar fashion from Æ-hydroxyalkylsilanes by treatment with carbon tetrabromide and triphenylphosphine, [41] phosphorus tribromide, [42] or dibromotriphenylphosphorane. [43] Scheme 6 Æ-Chloroalkylsilanes from Æ-Hydroxysilanes with Carbon Tetrachloride and Triphenylphosphine [40] OH R 1 SiMe 2Ph 21 CCl 4, Ph 3P Cl R 1 SiMe 2Ph 22 R1 = (CH2)4Me 85% R1 = (CH2) 6Me 87% R1 = Cy 82% R1 = Ph 65% (1-Chlorohexyl)dimethylphenylsilane [22, R 1 =(CH 2) 4Me]; Typical Procedure: [40] A soln of the Æ-hydroxysilane 21 [R 1 =(CH 2) 4Me; 18.77 g, 80 mmol] and Ph 3P (27 g, 100 mmol) in THF (300 mL) and CCl 4 (50 mL) (CAUTION) was heated under reflux for 6 h in a flask under an atmosphere of argon. After cooling the solvent was removed by vacuum distillation. The residue was extracted with hexanes (3 ” 300 mL). Evaporation and chromatography (silica gel, hexanes) of the residue gave the Æ-chlorosilane 22 as a colorless oil; yield: 17.2 g (85%). 4.4.27.2.3 Variation 3: Iodination of Æ-Hydroxyalkylsilanes with Methyl(triphenoxy)phosphonium Iodide Barrett and co-workers also found that Æ-iodoalkylsilanes can be prepared by reaction with methyl(triphenoxy)phosphonium iodide (e.g., 23 fi 24, Scheme 7). [44] These compounds are of limited synthetic value in the Peterson reaction, since iodine/metal exchange is difficult. Nevertheless the method for their preparation is a rare and potentially important one. Scheme 7 Æ-Iodoalkylsilanes from Æ-Hydroxyalkylsilanes [44] ( ) 4 23 OH SiMe3 (PhO)3PMeI 96% (1-Iodohexyl)trimethylsilane [24,R=(CH 2) 4Me]; Typical Procedure: [44] DMF (20 mL) was added to the crude alcohol 23 [R = (CH 2) 4Me; 5 mmol] under dry N 2.To this soln was added (PhO) 3PMeI (3.39 g, 7.5 mmol) and the mixture stirred for 12 h in the dark. MeOH (2 mL) and sat. aq Na 2S 2O 3 (1 mL) were added successively. The resulting mix- ( ) 4 24 I SiMe 3 for references see p 159
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Science of Synthesis Houben-Weyl Me
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8 Science of Synthesis Category 1:
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Volume 1: Compounds withTransition
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Table of Contents Volume 2 13 Volum
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Table of Contents 15 Volume 4: Comp
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Table of Contents 17 4.4.27 Product
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2001 Georg Thieme Verlag Rüdigerst
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1.1 Product Class 1: Organometallic
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1.1 Product Class 1: Organometallic
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1.1.1 Nickel Complexes of 1,3-Diene
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1.1.1 Nickel Complexes of 1,3-Diene
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1.1.2 Nickel-Allyl Complexes 37 tra
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1.1.2 Nickel-Allyl Complexes 39 Bis
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1.1.2 Nickel-Allyl Complexes 41 App
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1.1.2 Nickel-Allyl Complexes 43 NiC
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1.1.2 Nickel-Allyl Complexes 45 Sch
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1.1.2 Nickel-Allyl Complexes 47 Sch
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1.1.3 Nickel-Alkyne Complexes 49 Ca
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1.1.3 Nickel-Alkyne Complexes 51 (2
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1.1.3 Nickel-Alkyne Complexes 53 Sc
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1.1.3 Nickel-Alkyne Complexes 55 at
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1.1.3 Nickel-Alkyne Complexes 57 Sc
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1.1.3 Nickel-Alkyne Complexes 59 en
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1.1.3 Nickel-Alkyne Complexes 61 of
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1.1.4 Nickel-Alkene Complexes 63 Bi
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1.1.4 Nickel-Alkene Complexes 65 Sc
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1.1.4 Nickel-Alkene Complexes 67 1.
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1.1.4 Nickel-Alkene Complexes 69 Sc
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1.1.4 Nickel-Alkene Complexes 71 [5
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1.1.4 Nickel-Alkene Complexes 75 4-
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References 79 References [1] Chetcu
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References 81 [98] Tsuda, T.; Mizun
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86 Biographical Sketches Rinaldo Po
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88 2.6.4.2.2 Variation 2: Two-Elect
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90 2.6 Product Class 6: Organometal
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92 Science of Synthesis 2.6 Complex
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Page 166 and 167: 166 Biographical Sketches Alan Spiv
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Page 176 and 177: 176 References [43] Eaborn, C.; Var
Page 178 and 179: 178 Abbreviations Chemical (cont.)
Page 180 and 181: 180 Abbreviations Ligands (cont.) 2
Page 182: 182 Abbreviations General (cont.) q
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