Allylsilanes

Trimethyl[(Z)-3-(trimethylsilyl)oct-1-enyl]silane (176); Typical Procedure: [231]
Into a dry, N 2-flushed, 50-mL, three-necked flask was placed 1,3-bis(trimethylsilyl)oct-1yne
(175; 1.75 g, 7.0 mmol) and anhyd Et 2O (3.5 mL). To the soln was added neat DIBAL-H
(1.4 mL, 7.6 mmol), while the temperature during the addition was maintained at 25±
308C bymeans of a water bath. The soln was stirred at 408C for 2 h. The alkenylaluminum-containing
mixture was cooled to rt, and was then added through a double-ended
needle to a vigorouslystirred mixture of 10% aq HCl (15 mL), ice (15 g), and pentane
(15 mL). The mixture was stirred for 15 min, the organic phase that formed was separated,
and the aqueous phase was extracted with pentane (2 ” 15 mL). The combined organic extracts
were washed successivelywith ice-cold 10% HCl (20 mL), H 2O (20 mL), and brine
(20 mL), and then dried (MgSO 4). The solvents were removed and the residue was distilled
through a short Vigreux column; yield: 1.59 g (89%); bp 86±87 8C/2 Torr.
4.4.40.44 Method 44:
From Prop-2-ynylsilanes by Hydroboration
Although hydroalumination±protonolysis (Section 4.4.40.43) is the method of choice for
the reduction of simple alk-2-ynylsilanes, it is not a good method for trimethyl(1-pentylprop-2-ynyl)silane
(177). Indeed, the use of various stoichiometries of diisobutylaluminum
hydride in a hydrocarbon or ether solvent for the hydroalumination of alkyne
177 leads to only modest yield of the corresponding alkenylalane. However, hydroboration
of 177 with bis(1,2-dimethylpropyl)borane, followed by protonolysis of the
intermediate alkenylborane, gives allylsilane 178 in good yield (Scheme 69). [231] These
conditions can also be used for the preparation of allylsilane 176 from bis(silyl)alkyne
175 in 87% yield (GC).
Scheme 69 Allylsilanes by Hydroboration of Prop-2-ynylsilanes [231]
Me 3Si
( ) 4
177
FOR PERSONAL USE ONLY
890 Science of Synthesis 4.4 Silicon Compounds
1. , THF, 0−25
2
HB
2. AcOH
3. H2O2 79%
oC Trimethyl(1-pentylallyl)silane (178); Typical Procedure: [231]
To a stirred 1.5 M soln of bis(1,2-dimethylpropyl)borane (3.4 mL, 5.1 mmol) in THF was
added trimethyl(1-pentylprop-2-ynyl)silane (177; 0.9 g, 5.0 mmol) at 08C. The resultant
mixture was stirred at 0±5 8C for 30 min and then at rt for an additional 30 min. The resultant
alkenylborane was treated with glacial AcOH (0.6 mL) and was then heated at 65±
708C for 2 h. The remaining 1,2-dimethylpropyl groups on boron were oxidized with 3 M
NaOAc (6 mL) and 30% H 2O 2 (1.4 mL) at 35±40 8C. The mixture was maintained for 30 min
at rt, saturated with K 2CO 3, and then extracted with Et 2O (2 ” 10 mL). The combined extracts
were washed with brine (20 mL), dried (MgSO 4), and concentrated. The residue was
distilled through a short Vigreux column; yield: 0.72 g (79%); bp 63±64 8C/4 Torr.
( ) 4
SiMe 3
4.4.40.45 Method 45:
From Alk-2-ynylsilanes by Catalytic Hydrogenation
A widelyused procedure for the preparation of Z-3-substituted allylsilanes is by catalytic
hydrogenation of the corresponding alkynylsilanes. Hydrogenation is normally run in the
presence of a palladium catalyst such as the Lindlar catalyst, [232] but P-2 nickel (nickel boride)
can also be used in the preparation of Z-allylsilane 180 (Scheme 70). [233]
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG
178