Allylsilanes

Z-Vinylsilanes carrying a (tributylstannyl)methoxy substituent in the 3-position provide
E-allylsilanes on exposure to alkyllithium by a Still±Wittig rearrangement. [272]
Allylsilanes are available by rhodium(I)- and iridium(I)-catalyzed migration of C=C
bonds in silylated alkenes. [273]
Allylsilanes are available from allylic methyl ethers by reaction of the latter with photochemically
generated dimethylsilanediyl from dodecamethylcyclohexasilanes. [274,275]
An ingenious method is available for the transformation of á- orâ-pinene to 7-(trimethylsilyl)-á-pinene
byan ene reaction with N-sulfinylbenzenesulfonamide, followed
byreductive silylation. [264]
A direct transformation of allylic acetates to allylsilanes makes use of transition-metal-catalyzed
coupling of the former with tris(trimethylsilyl)aluminum±diethyl ether complex;
the method is chemoselective in that acetals, esters, enones, and isolated C=C
bonds remain unaffected, but this reaction is not always highly regio- or stereoselective.
[276]
Allylsilanes can be made from the crystalline ð-allylnickel halide complex available
from the reaction between [2-(bromomethyl)allyl]trimethylsilane and bis(1,5-cyclooctadiene)nickel(0)
with a varietyof organic halides in dimethylformamide. [277]
Allylsilanes are available from acrylic acid or the corresponding ester carrying a trimethylsilyl
group in the 3-position by treatment with diazoalkanes. [278]
Applications of Product Subclass 40 in Organic Synthesis
The widespread use of allylsilanes in organic synthesis has been covered in several reviews,
[9±30] and no attempt will be made to duplicate these efforts here. Rather, in this section,
the applications of some allylsilanes available by the methods described earlier (Sections
4.4.40.1±4.4.40.53) in organic synthesis will be illustrated, so as to enable the reader
to appreciate the importance of their specific method of preparation. In the process, a few
examples of the major reactions of allylsilanes will be highlighted.
4.4.40.55 Method 55:
Protodesilylation of Allylsilanes
Regio- and stereoselective synthesis of alkenes is possible by desilylation of an allylsilane
bya protic acid. For this, a number of conditions are available, of which the use of the boron
trifluoride±acetic acid complex is the preferred one; [20,21,30] it is used, for example, in
the formation of alkene 215 from allylsilane 86B (Scheme 81). [21,147] Stereochemicallydefined
allylsilane 86B, available from an allyl acetate by displacement with a silylcuprate
reagent (Section 4.4.40.22.1), was used to studythe stereochemistryof some S E2¢ reactions
of allylsilanes. In some specific cases, protodesilylation in the presence of a two-phase hydroiodic
acid in a benzene/water mixture is found to be the onlyuseful condition, [214,279] as
in the preparation of ester 217, an intermediate for a synthesis of ( )-methyl epijasmonate,
from silane 216 (Scheme 81). [214] This application in synthesis took advantage of
the method of preparation of allylsilanes described in Section 4.4.40.33.
Scheme 81 Protodesilylation of Allylsilanes [147,214]
Ph
86B
SiMe 2Ph
FOR PERSONAL USE ONLY
4.4.40 Allylsilanes 901
BF 3 2AcOH, CH 2Cl 2
92%
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG
Ph
H
215
for references see p 920