Allylsilanes

allylsilane 44 (Scheme 43). [154,155] Under these conditions, secondaryallylic halides, for example,
92, still give terminal E-allylsilanes, albeit contaminated with their regioisomers.
[155]
Regio- and stereodefined 3,3-disubstituted terminal allylsilanes have been prepared
from other silyllithium reagents, such as (dimethylphenylsilyl)lithium; hexamethylphosphoric
triamide is not required in these reactions, since the silyllithium reagents are prepared
in tetrahydrofuran. [163]
Scheme 43 Allylsilanes from Allyl Halides and Trimethylsilyllithium [80,154,155]
( ) 5
( ) 8
Cl
92
Cl
TMSLi, Et 2O, HMPA
78%
TMSLi, Et 2O, HMPA
Trimethyl[(E)-non-2-enyl]silane (44); Typical Procedure: [155]
MeLi·LiBr complex in Et 2O (1.6 mL, 2.5 mmol) was added dropwise to a soln of Me 3SiSiMe 3
(365 mg, 2.5 mmol) in HMPA (CAUTION: cancer suspect agent) (3 mL) at 0±5 8C under argon.
After stirring for 3 min, the resulting red soln was diluted with Et 2O (6 mL), cooled to
±60 8C, and stirred for 5 min. The color of the mixture changed from orange to yellow during
this time. A soln of 1-chloronon-2-ene (160 mg, 1 mmol) in Et 2O (1 mL) was added dropwise,
and the mixture was stirred for 1 h at ±60 to ±50 8C. The cold soln was poured into
pentane (50 mL) and sat. aq NH 4Cl (50 mL); the aqueous phase was extracted with petroleum
ether (3 ” 25 mL), and the combined organic extracts were dried (MgSO 4), filtered,
and concentrated. Purification bycolumn chromatography(silica gel, petroleum ether)
gave allylsilane 44; yield: 155 mg (78%).
4.4.40.25.2 Variation 2:
From Allyl Phosphates
Treatment of allylic phosphates with trimethylsilyllithium also gives allylsilanes, for
example, (E)-11 (Scheme 44). [156] Allylic phosphates have advantages over allylic halides,
especiallywith secondaryallylic substrates, for example, phosphate 93 used in the preparation
of silane 94. An additional advantage is that most allylic phosphates are stable
substrates and readily available from allylic alcohols in high yield. [164]
( ) 8
( )5
SiMe 3
44
+
19:81
SiMe 3
Scheme 44 Allylsilanes from Allyl Phosphates and Trimethylsilyllithium [156]
OPO(OEt)2
93
FOR PERSONAL USE ONLY
868 Science of Synthesis 4.4 Silicon Compounds
OPO(OEt) 2
TMSLi, Et2O, HMPA
−50 to −60 oC, 1 h
59%
TMSLi, Et2O, HMPA
−50 to −60 oC, 1 h
94
( )8
SiMe 3
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG
SiMe 3
(E)-11
SiMe 3