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