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154 Science of Synthesis 4.4 Silicon Compounds Dichloro(chloromethyl)silane (33): [64] CAUTION: Diazomethane is highly toxic and irritating. It is also a detonator and appropriate safety precautions should be taken when using this reagent (e.g., special glassware, use of a blast shield, etc.). For further details on the safe handling of diazomethane see refs [68,69] . Trichlorosilane (32; 40 g, 0.296 mol) in anhyd Et 2O (100 mL) in a 1-L three-necked flask equipped with a mechanical stirrer, a Y-joint holding a thermometer and a drying tube filled with Drierite, and a dropping funnel was cooled to –608C and Cu powder (0.5 g) added. A cold soln of CH 2N 2 (0.194 mol) in Et 2O (350 mL) was added slowly through the dropping funnel, with vigorous stirring of the mixture. N 2 evolution began immediately. After the addition was complete the mixture was stirred for 2 h between –65 to –608C under dry N 2. The mixture was allowed to warm to rt and stirred for a further 2 h. The Et 2O was removed by distillation through an 18-inch column packed with glass helixes. Another preparation of the same scale was performed and the residues combined and fractionally distilled to give dichloro(chloromethyl)silane (33); yield: 40 g (45% based on 32); bp 97.0–97.4 8C/773 Torr. 4.4.27.5 Method 5: Nucleophilic Substitution of Halo(haloalkyl)silanes Substitution at silicon of silanes already bearing bromomethyl or chloromethyl groups is a common process for preparing Æ-halomethylsilanes. The principle reason for the popularity of the method is the availability of chloro(chloromethyl)dimethylsilane and (bromomethyl)(chloro)dimethylsilane. [70] Nevertheless the reaction does work well with other halo(Æ-haloalkyl)silanes. [14,71] Addition of Grignard [14,72] and organolithium reagents occurs without the complication of substitution of the halogen at the Æ-position (e.g., 34 fi 35, Scheme 11). The method has been used to prepare Æ-halomethyl-substituted vinylsilanes from vinyl Grignard [73] and vinyllithum reagents. [74] Allyl, [75] alkynyl, [76] aryl, [77] and benzyl organometallic reagents also work well. Reaction of (bromomethyl)(chloro)dimethylsilane with alcohols and triethylamine [and sometimes 4-(dimethylamino)pyridine] is comm<strong>only</strong> used to prepare (bromomethyl)silyl ethers for radical cyclization. Scheme 11 Reaction of an Alkynyllithium Reagent with Chloro(chloromethyl)dimethylsilane [76] ( ) 5 1. BuLi 2. ClMe2Si 90% Cl ( ) 5 SiMe2 Cl 34 35 (Chloromethyl)(dimethyl)oct-1-ynylsilane (35); Typical Procedure: [76] 1.5 M BuLi in hexanes (37.3 mL, 55.9 mmol) was added at –788C to oct-1-yne (34; 6.15 g, 55.9 mmol) in THF (60 mL). The mixture was allowed to warm to 08C and stirred for 1 h, and then at rt for a further 15 min. The mixture was cooled to –788C. Chloro(chloromethyl)dimethylsilane (8.0 g, 55.9 mmol) in THF (20 mL) was added dropwise to the mixture over 1 h. The resulting mixture was stirred overnight at –788C. The mixture was allowed to warm to rt and sat. aq NH 4Cl (50 mL) was added and the mixture extracted with EtOAc (2 ” 100 mL). The organic extracts were washed with brine, dried (Na 2SO 4), and evaporated under reduced pressure. The residue was distilled to give (chloromethyl)(dimethyl)oct-1ynylsilane (35) as an oil; yield: 10.9 g (90%); bp 54–57 8C/3 Torr.
4.4.27 Æ-Haloalkylsilanes 155 4.4.27.6 Method 6: Alkylation of Æ-Haloalkylsilanes Æ-Haloalkylsilanes are deprotonated to provide an anion that reacts readily with haloalkanes (disconnection b, Scheme 1). The carbanion derived from (chloromethyl)trimethylsilane is stable at low temperature (decomposing slowly over 1 h at –408C) and reacts with a variety of electrophiles. Similar stability is evident for other members of the product class (36 fi 37, Scheme 12). Æ-Haloalkylsilanes are most comm<strong>only</strong> deprotonated with sec-butyllithium at –788C in the presence of N,N,N¢,N¢-tetramethylethylenediamine (TMEDA). [78–80] Under these conditions Æ-elimination is not a competing reaction. Scheme 12 Alkylation of (Chloromethyl)silanes [78] PhMe2Si Cl 1. s-BuLi, TMEDA, −78 oC 2. MeI 66% PhMe 2Si 36 37 (1-Chloroethyl)(dimethyl)phenylsilane (37); Typical Procedure: [78] 1.4 M s-BuLi in cyclohexane/isopentane (92:8) (164 mL, 0.230 mol) was added dropwise over 1.5 h to (chloromethyl)(dimethyl)phenylsilane (36; 40.0 g, 0.217 mol) in THF (260 mL) at –788C. TMEDA (24.1 g, 0.21 mol) was added dropwise to the resulting mixture over 20 min, maintaining the temperature at –788C. The soln was stirred for 1 h at –788C and then allowed to warm to –558C. MeI (41.2 g, 0.29 mol) in THF (70 mL) was added dropwise over 1 h, and the mixture stirred for a further 40 min at –408C and then 16 h at rt. The mixture was added carefully to cold sat. aq NH 4Cl (700 mL) and extracted with Et 2O (3 ” 350 mL). The combined organic extracts were washed with H 2O, dried (Na 2SO 4), and evaporated under reduced pressure. The residue was distilled to give the silane 37 as an oil; yield: 28.3 g (66%); bp 768C/6 Torr. Applications of Product Subclass 27 in Organic Synthesis The Grignard reagents derived from Æ-haloalkylsilanes have found widespread use in organic synthesis. Perhaps the most common application of (chloromethyl)trimethylsilane [14] is as a methylenating agent in the Peterson reaction. [81] In this reaction addition of the Grignard reagent 38 to carbonyl compounds generates an alcohol 39, from which an alkene 40 is produced by base-catalyzed elimination (Scheme 13). The process offers a useful alternative to the Wittig reaction. The Grignard reagents derived from Æ-haloalkylsilanes are particularly useful for preparing â-ketosilanes, which are themselves useful in the stereoselective version of the Peterson alkenation reaction. [82] For example, the Grignard reagent derived from (Æ-chloroalkyl)(dimethyl)phenylsilane 22 reacts with acyl chlorides [with copper(I) catalysis] to give the ketone 41. Reaction of this ketone with an organometallic reagent (R 3 M) followed by potassium hydride or 4-toluenesulfonic acid yields either stereoisomer of the trisubstituted alkene (Scheme 13). A related process has shown that (iodomethyl)trimethylsilane generates alkenes directly from ketones by the use of samarium(II) trifluoromethanesulfonate. [83] (Æ-Silylalkyl)lithiums are produced from Æ-haloalkylsilanes via transmetalation by reaction with an alkyllithium [42] or by direct reaction with lithium metal. [19,84] Cl for references see p 159
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Science of Synthesis Houben-Weyl Me
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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 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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100 Science of Synthesis 2.6 Comple
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Page 166 and 167: 166 Biographical Sketches Alan Spiv
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Page 170 and 171: 170 Science of Synthesis 5.1 German
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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