Allylsilanes

10% aq HCl and sat. aq NaHCO 3, and dried (MgSO 4). After the solvent had been removed in
vacuo, the residue was flash chromatographed (pentane); yield: 271 mg (50%).
4.4.40.7.2 Variation 2:
From Enol Phosphates with [(Trialkylsilyl)methyl]magnesium Halides
Nickel acetylacetonate catalyzed cross coupling of enol phosphates with [(trialkylsilyl)methyl]magnesium
halides offers a reliable route to allylsilanes, for example, silane
35 (Scheme 17). [86] A varietyof other transition-metal catalysts such as nickel(II) bromide
and tetrakis(triphenylphosphine)palladium(0) have been found to be equally useful for
such coupling reactions. The required enol phosphates have been prepared bythe addition
of diethyl chlorophosphate to the lithium enolate, generated from a ketone and lithium
diisopropylamide under kinetically controlled conditions. [86] Of note is the compatibilityof
this protocol with reactive functional groups, [87,88] as shown by, for example, the
preparation of silane 36 (Scheme 17). [87]
Scheme 17 Allylsilanes from Enol Phosphates [86,87]
OPO(OEt) 2
CO2Me
OPO(OEt)2
FOR PERSONAL USE ONLY
848 Science of Synthesis 4.4 Silicon Compounds
Me3SiCH2MgCl Ni(acac) 2 (cat.), 15 h
81%
Me3SiCH2MgCl Ni(acac) 2 (cat.)
35
SiMe 3
36
SiMe3
CO2Me
Conversion of Enol Phosphates into Allylsilanes; General Procedure: [86]
Into a 50-mL flask, equipped with a stirring bar, were successivelyadded the catalyst (0.1±
0.15 mmol), a soln of Me 3SiCH 2MgCl (5±9 mmol) in Et 2O, and the enol phosphate
(3 mmol). The flask was sealed with a serum cap. The mixture was stirred at rt for 15 h
and hydrolyzed with dil HCl (15 mL) under cooling with an ice bath. The organic layer
was separated and the aqueous layer was extracted with Et 2O (2 ” 220 mL). The combined
organic layers were washed with sat. aq NaHCO 3 (30 mL) and H 2O, and dried (Na 2SO 4). The
solvent was removed under reduced pressure and the allylsilane was isolated by distillation
in vacuo and/or column chromatography(silica gel, hexane).
(Cyclohex-1-enylmethyl)trimethylsilane (35); yield: 81%; bp 708C/5 Torr.
4.4.40.7.3 Variation 3:
From Vinyl Trifluoromethanesulfonates with
Tris[(trimethylsilyl)methyl]aluminum
Allylsilanes, for example, 38 and 39 (Scheme 18), are available bypalladium(0)-catalyzed
cross coupling of vinyl trifluoromethanesulfonates (triflates) with tris[(trimethylsilyl)methyl]aluminum,
generated in situ from 3 equivalents of [(trimethylsilyl)methyl]lithium
and 1 equivalent of aluminum trichloride. [89] Besides the high stereospecificityof
this procedure, its compatibilitywith the presence of a host of reactive functional groups
in substrates is noteworthy.
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG