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Chemistry Letters Vol.36, No.12 (2007)
Deoxygenative Allylation of Benzyl Acetates and Cinnamyl Alcohols
Catalyzed by Molecular Iodine
J. S. Yadav,ꢀ B. V. Subba Reddy, A. Srinivas Reddy, and B. Eeshwaraiah
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad-500 007, India
(Received August 6, 2007; CL-070839; E-mail: yadavpub@iict.res.in)
Benzyl acetates undergo smooth deoxygenative allylation
with allyltrimethylsilane in the presence of 10 mol % of molecu-
lar iodine under mild conditions to afford the corresponding allyl
derivatives in excellent yields and with high selectivity. Cinnam-
yl alcohols also react readily with allylsilane under similar con-
ditions. The use of molecular iodine makes this method quite
simple, more convenient and cost effective.
yields at room temperature under the influence of 10 mol % of
iodine. Interestingly, doubly activated alcohols reacted readily
with allyltrimethylsilane to furnish allyl derivatives in excellent
yields (Entries L–O, Table 1, Scheme 2).
Simple secondary cinnamyl alcohols also participated well
in this reaction (Entries P and Q, Table 1). Unlike benzyl alco-
hols, cinnamyl alcohols do not require any activating group like
acetate to proceed the reaction. However, the allylation of cin-
namyl alcohols gave mixture of products arising from ꢀ-substi-
tution as a result of allylic rearrangement, SN20-type substitution
(Entries P and Q, Table 1). This method is compatible with es-
ters, amides, halides, aryl alkyl ethers, alkynes, and alkenes pres-
ent in the molecule. The simple alkyl acetates failed to undergo
allylation under the reaction conditions. This method was suc-
cessful with secondary benzyl acetates and cinnamyl alcohols.
As solvent, dichloromethane appeared to give the best results.
All products were characterized by 1H, 13C NMR, IR, and mass
spectrometry. However, in the absence of catalyst, the reaction
did not proceed even after a long reaction time. Interestingly,
catalytic amount of TMSI was also found to be equally effective
catalyst for this conversion. However, the use of allyltri-n-butyl-
tin in place of allyltrimethylsilane did not yield the desired prod-
uct under these reaction conditions, perhaps because iodine does
not interact with allyltri-n-butyltin. Thus, the combination of al-
lyltrimethylsilane and iodine could be the method of choice for
allylation of benzyl acetates and cinnamyl alcohols.9 No addi-
tives or acidic promoters are required for the reaction to proceed.
The catalyst is readily available at low cost and is highly efficient
in promoting allylations. Substituted allyltrimethylsilane also re-
acted well with cinnamyl alcohols to provide methyl-substituted
1,5-dienes (Entries R and S, Table 1). The scope of this process
is illustrated with respect to various benzyl acetates and cinnam-
yl alcohols and the results are presented in Table 1.10
The stereoselective addition of allylsilanes to aldehydes, re-
ferred to as the Sakurai–Hosomi reaction has been recognized as
one of the most efficient methods for carbon–carbon bond-form-
ing reaction and has been extensively applied in organic synthe-
sis, especially in natural products synthesis.1,2 Acid-catalyzed
carbon–carbon bonding forming reactions are of great signifi-
cance in organic synthesis because of their high reactivity, selec-
tivity and mild reaction conditions.3 Benzyl acetates are well-
known carbon electrophiles capable of reacting with various nu-
cleophiles and their ability to undergo nucleophilic substitution
reactions contributes largely to their synthetic value.4,5 In recent
years, various methods have been reported using Brønsted acids
as well as transitions metals.6 However, there have been no re-
ports on the allylation of benzyl acetates and cinnamyl alcohols
with allyltrimethylsilane using molecular iodine. Recently, mo-
lecular iodine has received considerable attention as a readily
available and cost-effective reagent for various organic transfor-
mations, affording the corresponding products with high selec-
tivity in excellent yields. The mild Lewis acidity associated with
iodine has led to its use in organic synthesis using catalytic to
stoichiometric amounts.7
In continuation of our interest on the use of molecular iodine
for various organic transformations,8 we describe herein an effi-
cient method for the allylation of benzyl acetates and cinnamyl
alcohols using allyltrimethylsilane with the aid of catalytic
amount of molecular iodine. In a preliminary experiment, tetra-
hydronaphthalen-1-yl acetate (1) was treated with allyltrimethyl-
silane (2) in the presence of 10 mol % of molecular iodine. The
reaction went to completion within 1.5 h at room temperature
and the product 3F was obtained in 82% yield (Scheme 1).
Similarly, a wide range of benzyl acetates underwent
smooth allylation with allyltrimethylsilane to afford the corre-
sponding pent-4-en-2-yl benzene derivatives in high yields (En-
tries A–K, Table 1). In all cases, the reactions proceed in high
In summary, we have developed a mild, convenient and ef-
ficient protocol for the allylation of benzyl acetates and cinnamyl
alcohols using a catalytic amount of molecular iodine. In addi-
tion to its efficiency, simplicity, and mild reaction conditions,
this method provides high yields of products with high selectiv-
ity, which makes it a useful and attractive process for the synthe-
sis of allylation of benzyl acetates and cinnamyl alcohols.
ASR and BE thank CSIR, New Delhi for the award of the
fellowships.
OAc
10 mol% I2
OH
10 mol % I2
Si
+
Si
CH2Cl2, r.t.
+
CH2Cl2, r.t.
1
2
3F
3L
Scheme 1.
Scheme 2.
Copyright Ó 2007 The Chemical Society of Japan