Catalysis of electrophilic addition of alcohols to Alkoxyalkenes by Lithium Salts

Full text of DOI:10.1023/A:1012384313049

Russian Journal of General Chemistry, Vol. 71, No. 2, 2001, pp. 319 320. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 2, 2001,
pp. 349 350.
Original Russian Text Copyright
2001 by Trofimov, Oparina, Gorelova, Parshina, Gusarova.
LETTERS
TO THE EDITOR
Catalysis of Electrophilic Addition of Alcohols
to Alkoxyalkenes by Lithium Salts
B. A. Trofimov, L. A. Oparina, O. V. Gorelova, L. N. Parshina, and N. K. Gusarova
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences, Irkutsk, Russia
Received May 4, 2000
The examples of bytoxyethene and 1-butanol were
used to show for the first time that neutral lithium
salts [CF3SO3Li, LiBr, LiN(SO2CF3)2] can be used
to success as catalysts in electrophilic addition rea-
ctions of proton-donor reagents to electronically sa-
turated alkenes. Such reactions are usually catalyzed
by acids.
lithium salts no adduct is formed, implying that the
lithium cation catalyzes alcohol addition to a nucleo-
philic double bond. Hence, this fact principally com-
plements the scarce data on the use of lithium com-
plexes (for example, LiClO4 diethyl ether) in organic
synthesis, in particular in the Diels Alder [3, 4] and
Michael [5] reactions, aldol condensation [6], acetali-
zation of aldehydes [7], and polymerization of vinyl
ethers [8].
The addition takes place on heating (60 90 C) of
equimolar amounts of the reagents in the presence of
1 10 wt % of a lithium salt (dissolved in 1,2-di-
methoxyethane) and gives 1,1-dibutoxyethane in an
yield of up to 90%. Lithium trifluoromethanesulfonate
is a more effective catalyst than lithium bromide or
lithium bis(trifluoromethanesulfonyl)amide.
Mechanistically, the catalysis of electrophilic addi-
tion to alkoxyalkenes by neutral lithium salts is
evidently similar to the catalysis by protons and Lewis
acids. It is based on polarization of alkoxyalkene by
complex formation with the electronically saturated
double bond, as well as with the neighboring oxygen
atom. The catalytic activity of lithium salts is in-
creased in such solvents as 1,2-dimethoxyethane,
acetals, oligoethyleneglycol ethers, etc., capable of
complex formation with the lithium cation.
OBu-n
Li+
CH2=CHOBu-n + n-BuOH
Me CH
.
OBu-n
Under the same conditions in the absence of
Me
O
Li+
Me
O
Me
O
R
, ROH
O Me
O
O
Li
O
R
R
Me O
O
O
Me
O
Me
Me
H
The role of the complex-forming solvent for
lithium salt (for example, 1,2-dimethoxyethane) is to
separate the ion pair and to weaken the bond between
the lithium cation and the anion, thus increasing the
electrophilicity of the latter. In terms of this concept,
lithium salts with bulky complex anions and delo-
calized negative charge must have increased catalytic
activity, which is indeed the case. Hence, it is safe to
state that complexes of lithium salts will find wide
use in organic synthesis as a special group of soft
metal-complex catalysts.
Addition of 1-butanol to butoxyethene in the
presence of lithium trifluoromethanesulfonate. To a
1070-3632/01/7102-0319$25.00 2001 MAIK Nauka/Interperiodica

320
TROFIMOV et al.
mixture of 4.4 g of butoxyethene and 3.3 g of 1-buta-
nol, a 10% solution of CF3SO3Li (0.1 g, 1.4 wt %) in
1,2-dimethoxyethane was added. The resulting mix-
ture was stirred at 90 C for 4 h until complete con-
version of bytoxyethene (control by GLC). Dibutyl-
amine, 0.2 g, was then added, and the mixture was
distilled in a vacuum to obtain 6.9 g (90%) of 1,1-
dibutoxyethane. The reaction product was identified
by comparison with an authentic sample [9].
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Reaction in the presence of lithium bromide and
bis(trifluoromethanesulfonyl)amide. Heating of the
same reagents (60 C, 5 h) in the presence of 3 wt %
of LiBr and 1 wt % of LiN(SO2CF3)2 (10% solutions
in 1,2-dimethoxyethane) gives 1,1-dibutoxyethane in
95% yield (per reacted butoxyethene; the conversions
of butoxyethene were 19% and 37%, respectively).
Commercial lithium salts were dried in a vacuum.
Butoxyethene and 1,2-dimethoxyethane were distilled
over sodium. 1-Butanol was refluxed with CaO and
distilled. The reaction progress was followed by GLC
on an LHM-80 chromatograph, detector katharometer,
column 3000 3 mm, packing 1% of PEG 20000 on
NaCl, carrier gas helium.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 2 2001