Allylsilanes

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1. Me3Si SiMe3 2. Pd(dba)2 THF, rt 92% OCOCF3 69 70 OCOCF 3 1. Me3Si SiMe3 2. Pd(dba)2 THF, rt 89% Allylic acetates can replace the corresponding trifluoroacetates in these reactions only when an added chloride salt, for example, lithium chloride, is present in the reaction medium. However, the reactions proceed onlyat higher temperatures and are accompanied byreduced yields. [136] Configurational inversion is normally observed with cycloalkenyl trifluoroacetates. For example, methyl cis-5-trifluoroacetoxycyclohex-3-ene carboxylate (71) gives trans-72 in the tetrahydrofuran/acetonitrile mixed solvent. Note that this reaction is essentially solvent dependent, since use of pure tetrahydrofuran leads to a 1:1 mixture of trans- and cis-72 (Scheme 33). [136] 46 SiMe 3 Scheme 33 An Allylsilane from an Allyltrifluoroacetate with Stereochemical Inversion or Randomization [136] CO 2Me 71 OCOCF3 FOR PERSONAL USE ONLY 860 Science of Synthesis 4.4 Silicon Compounds Pd(dba)2 (cat.) Me3Si SiMe3 THF, MeCN 89% Pd(dba)2 (cat.) Me3Si SiMe3 THF 85% CO 2Me trans-72 CO 2Me trans-72 SiMe3 SiMe3 + 1:1 CO 2Me (2-Cyclohexylideneethyl)trimethylsilane (46); Typical Procedure: [136] A 20-mL flask was charged with Pd(dba) 2 (17 mg, 0.030 mmol) and THF (5.5 mL) under an argon atmosphere. The mixture was stirred, and the palladium complex dissolved, affording a deep-purple soln. Then Me 3SiSiMe 3 (293 mg, 2.0 mmol) and ester 69 (222 mg, 1.0 mmol) were added in this order. The mixture turned pale yellow, and the reaction was allowed to proceed at rt for 12 h. The mixture was then diluted with Et 2O (20 mL), washed with sat. aq NaHCO 3 (20 mL), dried (MgSO 4), and concentrated. Kugelrohr distillation afforded silane 46; yield: 168 mg (92%); bp 80 8C/1 Torr. 4.4.40.19.2 Variation 2: Using Samarium(II) Iodide and Chlorotrimethylsilane An alternative procedure for the preparation of terminallysubstituted allylsilanes involves palladium-catalyzed reductive metalation of allylic phosphates with the samarium(II) iodide±hexamethylphosphoric triamide complex. Thus, the E-allylsilane (E)-74 is available in good yield from (E)-73 (Scheme 34). [137] In general, low temperature is recom- cis-72 Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG SiMe3
mended for the synthesis of Z-allylsilanes, for example, in the preparation of (Z)-74 [contaminated with 3% (E)-74] from (Z)-73 with good regioselectivity[(á/ã) 95:5]. Use of the palladium catalyst is not mandatory, its presence only accelerates the reaction. Of note is the retention of the alkene geometry for geranyl- and nerylsilanes when the reactions are run even at room temperature, as, for example, in the preparation of (E)-11. Allyl acetates can also be used in this procedure, but are associated with reduced reaction rates and yields. [137] Scheme 34 Use of Samarium(II) Iodide and Chlorotrimethylsilane [137] ( )9 ( ) 9 (E)-73 OPO(OEt) 2 OPO(OEt) 2 FOR PERSONAL USE ONLY 4.4.40 <strong>Allylsilanes</strong> 861 TMSCl, SmI2 Pd(PPh3) 4 (cat.) THF, HMPA, 25 oC, 98:2 Trimethyl[(E)-tridec-2-enyl]silane [(E)-74]; Typical Procedure: [137] To a mixture of 0.1 M SmI 2 in THF (5 mL, 0.5 mmol), HMPA (0.35 mL, 2 mmol), and TMSCl (0.25 mL, 2 mmol) was added, successively, a soln of Pd(PPh 3) 4 (12.0 mg, 0.01 mmol, 5 mol%) in THF (0.45 mL) and phosphate (E)-73 (66.8 mg, 0.2 mmol). After the mixture had stirred for 1 min at rt, silica gel (ca. 1 g) and hexane (5 mL) were added. The mixture was passed through a short column (silica gel, Et 2O). The eluate was concentrated in vacuo and purified bycolumn chromatography(silica gel, hexane) to give (E)-74 with 1% of its Z-isomer; yield: 45.3 mg (89%). 4.4.40.20 Method 20: From Allyl Alcohols by Palladium(0)-Catalyzed Intramolecular Silylsilylation 1,3-Unsymmetrically substituted E-allylsilanes have been prepared by palladium-catalyzed intramolecular silylsilylation of allyl alcohols and subsequent Peterson-type elimination with organolithium reagents. This protocol involving 1,3 chiralitytransfer is equally applicable to the synthesis of enantioenriched allylsilanes. For example, the intramolecular silylsilylation of (R,E)-75 (99.7% ee) promoted bya catalyst generated in situ from bis(acetylacetonato)palladium(II) and 1,1,3,3-tetramethylbutyl isocyanide gives a 1:1 mixture of allylsilane (S,E)-78 (99.1% ee) and cyclic siloxane 77, presumablythrough the highlystereoselective formation of four-membered ring 76 followed byits thermal disproportionation (Scheme 35). [138,139] Subsequent treatment of the mixture with butyllithium yields allylsilane (S,E)-78 (99.1% ee) from 77 without contamination from its Z-isomer. Similarly, (R,E)-78 (95.4% ee) [138] is available from (R,Z)-75 (96.0% ee). The substrates for these reactions have been prepared byreactions of the corresponding alcohols with 1-chloro-1,1,2-triphenyl-2,2-dimethyldisilane in the presence of triethylamine and a catalytic amount of 4-dimethylaminopyridine. Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG SiMe 3 for references see p 920
Page 1 and 2: 4.4.40 Product Subclass 40: Allylsi
Page 3 and 4: matching of both partners is approp
Page 5 and 6: pressure. Flash chromatography(sili
Page 7 and 8: Scheme 11 From Allylic Halides by E
Page 9 and 10: similar protocol starting with but-
Page 11 and 12: + PhMe2Si MgCl Cl Br (R,S)-PPFA = +
Page 13 and 14: Scheme 18 Allylsilanes from Vinyl T
Page 15 and 16: Trimethyl(non-2-enyl)silane (44); T
Page 17 and 18: complex which reacts with the carbo
Page 19 and 20: (2-Cyclohexylidenepropyl)trimethyls
Page 21 and 22: (2 ” 10 3 kPa)±depressurization
Page 23: Scheme 31 Allylsilanes from Allyl A
Page 27 and 28: Allylsilanes 80; General Procedure:
Page 29 and 30: Scheme 39 Allylsilanes from Allyl C
Page 31 and 32: Scheme 42 2-Substituted Allylsilane
Page 33 and 34: FOR PERSONAL USE ONLY 4.4.40 Allyls
Page 35 and 36: Conversion of â-Hydroxy Acids 99 i
Page 37 and 38: Scheme 48 Allylsilanes by Carbocupr
Page 39 and 40: 119. [183,185] The trick for succes
Page 41 and 42: the mixture was washed with sat. aq
Page 43 and 44: (+)-(3R,4E)-N,N-Dimethyl-3-(trimeth
Page 45 and 46: Scheme 57 From Alkenyl Fischer Carb
Page 47 and 48: 4.4.40.37 Method 37: From Allyl Sul
Page 49 and 50: Allyltris(trimethylsilyl)silane (15
Page 51 and 52: the Z-isomer; very little, if any,
Page 53 and 54: Pd2(dba)3 CHCl3 (cat.) (R)-MOP-phen
Page 55 and 56: Scheme 70 An Alk-2-enylsilane by Ca
Page 57 and 58: (E)-Trimethyl[3-(4-tolyl)allyl]sila
Page 59 and 60: FOR PERSONAL USE ONLY 4.4.40 Allyls
Page 61 and 62: Scheme 77 2-Substituted Allylsilane
Page 63 and 64: stream of argon, which was passed t
Page 65 and 66: Z-Vinylsilanes carrying a (tributyl
Page 67 and 68: 1-tert-Butyl-1-vinylcyclohexane (21
Page 69 and 70: 4.4.40.59 Method 59: Allylation of
Page 71 and 72: (5SR,6SR,9RS,10RS)-6,9-Divinyltetra
Page 73 and 74: Scheme 97 Synthesis of Homoallylic
Page 75 and 76:
Scheme 102 Synthesis of Enantiomeri
Page 77 and 78:
Scheme 106 Diastereoselective Synth
Page 79 and 80:
stirred for 18 h at ±78 8C, and 5
Page 81 and 82:
shaken with some solid K 2CO 3 and
Page 83 and 84:
FOR PERSONAL USE ONLY 4.4.40 Allyls
Page 85 and 86:
FOR PERSONAL USE ONLY References 92
Page 87 and 88:
Page 89 and 90:
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Allylsilanes

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