Allylsilanes

(+)-(3R,4E)-N,N-Dimethyl-3-(trimethylsilyl)hex-4-enamide [(R)-132]: [203]
Alcohol 131 (1.04 g, 7.2 mmol; corrected for 15% contamination with its saturated analogue),
Me 2NCMe(OMe) 2 (3.1 mL, 20.9 mmol), and drybenzene (15 mL) were heated for
13 h in a sealed ampule under argon at 908C. Volatile materials were removed and the
crude product was chromatographed (silica gel, hexane/EtOAc 7:3) and then distilled (Kugelrohr,
75±80 8C/0.1 Torr) to give hexenamide (R)-132 as a colorless oil; yield: 1.455 g
(95%; corrected for contamination with starting material).
4.4.40.32 Method 32:
From 1-Trimethylsilyl-1,3-dienes by a Diels±Alder Reaction
Cyclic allylsilanes adorned with a choice of functional groups are accessible by Diels±Alder
reaction of 1-trimethylsilyl-1,3-dienes with various dienophiles, for example, the
preparation of allylsilane 134 (Scheme 55). [206±208] The silyl group exerts little directing influence
on the regioselectivityof the reaction with unsymmetrical dienophiles, this reaction
being governed byother substituents, if any, present on the dienes. [206±208] Indeed, the
weak directing effect of the trimethylsilyl group can be completely overwhelmed, as in
the synthesis of the single regioisomeric allylsilane 135, an intermediate used in a synthesis
of ( )-shikimic acid. [209] Intramolecular Diels±Alder reactions of substrates with a builtin
1-silyl-1,3-diene moiety have allowed access to more complex allylsilanes. [210,211]
Scheme 55 Allylsilanes from Terminally Silylated 1,3-Dienes [206±209]
SiMe 3
133
OAc
SiMe 3
O
+ O
+
O
CO2Me
FOR PERSONAL USE ONLY
4.4.40 Allylsilanes 879
95−100 oC, 30 min
74%
Me3Si H
OAc
SiMe 3
135
H
134
CO 2Me
3-(Trimethylsilyl)cyclohex-4-ene-1,2-dicarboxylic Anhydride (134); Typical Procedure: [208]
Diene 133 and maleic anhydride were mixed in equimolar amounts, allowing for any codistillate
with which the diene was contaminated; a crystal of hydroquinone was added,
and the mixture was stirred at 95±1008C for 0.5 h under N 2. The product was crystallized
from cyclohexane to give anhydride 134 as plates; yield: 74%; mp 125±1268C.
4.4.40.33 Method 33:
Formation of Cyclopentanoid Allylsilanes by an Intramolecular Ene Reaction
cis-1,2-Disubstituted cyclopentanoid E-allylsilanes, for example, 138, have been prepared
with high diastereoselectivity by thermolytic ene cyclization of activated 1,6-dienes, for
example, 136, featuring a homoallylsilane unit as ene donor (Scheme 56). [212,213] Note
that the yield of this reaction suffers if air is not purged properly with argon. Also, diene
136 (R 1 =R 3 =H;R 2 =R 4 = Me) fails to give the corresponding silane 138, even at elevated
temperatures for a longer reaction period. The exclusive formation of E-allylsilanes is
explicable in terms of transition state 137. The failure of 136 (R 1 =R 3 =H;R 2 =R 4 = Me) towards
cyclization is presumably due to unavoidable 1,3-diaxial interactions involving a
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG
O
O
O
for references see p 920