Stereoselective synthesis of analogs of natural isoprenoids based on the reaction of alkyl 4-dialkoxyphosphoryl-3-methylbut-2-enoates with aldehydes in ionic liquids and in an imidazolium salt - Benzene system

Article abstract of DOI:10.1023/B:RUCB.0000035653.43049.35

Condensation of alkyl 4-dialkoxyphosphoryl-3-methylbut-2-enoates with a number of aldehydes under the Horner - Emmons reaction conditions in 1-butyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate and in 1-butyl-3-methylimidazolium bromide - benzene and 1-butyl-2,3- dimethylimidazolium hexafluorophosphate - benzene systems was studied. The E/Z-stereoisomer ratio of the olefination products for the reaction carried out in ionic liquids was 3:1, which corresponds to the values attained previously in the KOH - benzene - Bu₄ⁿNBr (cat.) system. Quantum-chemical calculations were used to determine the averaged radii (r ₀) of the [Bu₄ⁿN] and substituted imidazolium cations by means of the Gaussian 98 program package. The stereoselectivity of olefination in the KOH - PhH - phase-transfer catalyst system decreases with a decrease in the r₀ value for the catalyst cation. The possibility of recovery and reuse of ionic liquids is demonstrated.

Full text of DOI:10.1023/B:RUCB.0000035653.43049.35

Russian Chemical Bulletin, International Edition, Vol. 53, No. 3, pp. 659—664, March, 2004
659
Stereoselective synthesis of analogs of natural isoprenoids
based on the reaction of alkyl 4ꢀdialkoxyphosphorylꢀ3ꢀmethylbutꢀ2ꢀenoates
with aldehydes in ionic liquids and in an
imidazolium salt—benzene system
S. G. Zlotin,ꢀ G. V. Kryshtal, G. M. Zhdankina, P. A. Belyakov, and E. P. Serebryakov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Еꢀmail: zlotin@ioc.ac.ru
Condensation of alkyl 4ꢀdialkoxyphosphorylꢀ3ꢀmethylbutꢀ2ꢀenoates with a number of
aldehydes under the Horner—Emmons reaction conditions in 1ꢀbutylꢀ3ꢀmethylimidazoꢀ
lium hexafluorophosphate and tetrafluoroborate and in 1ꢀbutylꢀ3ꢀmethylimidazolium broꢀ
mide—benzene and 1ꢀbutylꢀ2,3ꢀdimethylimidazolium hexafluorophosphate—benzene systems
was studied. The E/Zꢀstereoisomer ratio of the olefination products for the reaction carried out
in ionic liquids was 3 : 1, which corresponds to the values attained previously in the
n
КOH—benzene—Bu4 NBr (cat.) system. Quantumꢀchemical calculations were used to deterꢀ
mine the averaged radii (r0) of the [Bu4nN] and substituted imidazolium cations by means of the
Gaussian 98 program package. The stereoselectivity of olefination in the KOH—PhH—phaseꢀ
transfer catalyst system decreases with a decrease in the r0 value for the catalyst cation. The
possibility of recovery and reuse of ionic liquids is demonstrated.
Key words: alkyl 2,4ꢀdienoates, isoprenoids, juvenoids, hydroprene, methoprene,
Horner—Emmons reaction, ionic liquids, aldehydes.
The reactions of aldehydes with alkyl 4ꢀdialkoxyꢀ
phosphorylꢀ3ꢀmethylbutꢀ2ꢀenoate (1) are used in the synꢀ
thesis of biologically active polyunsaturated isoprenoids
for the elongation of the carbon chain by one funcꢀ
tionalized isoprenoid unit.1 This reaction is complicated
by stereomutation of the double bond in compound 1
under the action of the base needed for the generation of
the carbanion; as a result, even in the case of stereoꢀ
chemically pure starting compounds, the reactions result
in binary mixtures of 2Z and 2E stereoisomers of the
olefination products. As to the newly formed double bond
in position 4, this always has the Eꢀconfiguration. Develꢀ
opment of methods for stereochemical control of this
reaction is important, as the most active antikeratitis and
immunoregulatory agents of the retinoic acid group and
juvenoids (methoprene, hydroprene) containing polyene
isoprenoid fragments available by olefination have Eꢀconꢀ
figurations of all double bonds.2
(in particular, tetraalkylammonium salts).4 These data
prompted the idea of using structurally related 1,3ꢀdialkylꢀ
imidazolium salts (currently wellꢀknown under the name
"ionic liquids"5,6) as solvents and catalysts in the stereoꢀ
selective synthesis of isoprenoid dienoic esters by the
Horner—Emmons—Wadsworth reaction. Indeed, our preꢀ
liminary results showed that ester 1a reacts with 3ꢀmethylꢀ
butanal (2) or 3,7ꢀdimethyloctanal (4) in 1ꢀbutylꢀ3ꢀ
methylimidazolium hexafluorophosphate [bmim][PF6] in
the presence of LiOH•H2O to give the corresponding
2E,4Eꢀdienes 3 and 5 as the major products.7
The purpose of this work is to study in more detail the
influence of the structure of the ionic liquid, phosphonꢀ
ate 1, and the type of base used on the stereoselectivity of
the reaction of alkyl 4ꢀdialkoxyphosphorylꢀ3ꢀmethylbutꢀ
2ꢀenoates 1a,b with aldehydes in imidazolium salts and in
imidazolium salt—benzene systems.
The reactions were carried out with aldehydes of the
isoprenoid series, 3ꢀmethylbutanal (2), 3,7ꢀdimethylꢀ
octanal (4), and 7ꢀmethoxyꢀ3,7ꢀdimethyloctanal (6),
and with benzaldehyde (7). Readily available 1ꢀbutylꢀ
3ꢀmethylimidazolium salts that are now under intenꢀ
sive research were used as ionic liquids, namely, 1ꢀbutylꢀ
3ꢀmethylimidazolium bromide ([bmim][Br]),8 hexaꢀ
fluorophosphate ([bmim][PF6]),9 and tetrafluoroborate
Previously, it has been shown that in the condensation
of ethyl 4ꢀdiethoxyphosphorylꢀ3ꢀmethylbutꢀ2ꢀenoate
(1a) with 3ꢀmethylbutanal (2), the proportion of the
2E,4E isomer in the reaction product (3) increases on
passing from hydrocarbon to polar aprotic solvents
(MeCN, DMF, DMSO)3 and also when the reaction is
carried out in the presence of phaseꢀtransfer catalysts
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 629—634, March, 2004.
1066ꢀ5285/04/5303ꢀ0659 © 2004 Plenum Publishing Corporation

660
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 3, March, 2004
Zlotin et al.
([bmim][BF4])10 and 1ꢀbutylꢀ2,3ꢀdimethylimidazolium
hexafluorophosphate ([bdmim][PF6]).11 Deprotonation of
CHꢀacids 1a,b was accomplished by treatment with LiOH,
KOH, and 1ꢀbutylꢀ3ꢀmethylimidazolium hydroxide
([bmim][OH])12 (LiOH was taken as the monohydrate).
It should be noted that the ester group in the allylic
phosphonates 1a,b, unlike that in triethyl phosphonoꢀ
acetate,7 is not saponified by КOH in the ionic liquid
and, hence, this base can be used for olefination.
It was found that the use of ionic liquids changes the
regularities of olefination established previously for reacꢀ
tions carried out in molecular organic solvents.1 For exꢀ
ample the nature of the base does not influence the yield
or the ratio of 2E,4E to 2Z,4E stereoisomers (3 : 2) in
product 3 when 3ꢀmethylbutanal (2) is olefinated with
ethyl 4ꢀdiethoxyphosphorylꢀ3ꢀmethylbutꢀ2ꢀenoate (1a) in
[bmim][PF6] (Table 1). The Еꢀselectivity of the reaction
in ionic liquids is higher than that in benzene but is lower
than in DMSO.3
The stereochemical outcome of the reactions of esters
1a,b with aldehydes depends on whether the reaction is
carried out directly in an ionic liquid medium or in the
imidazolium salt—benzene system. Whereas the ratio of
2E,4E to 2Z,4E stereoisomers in product 5 formed upon
olefination of 3,7ꢀdimethyloctanal (4) with phosphonate
1a in [bmim][PF6] equals 3 : 1, in the reaction carried out
in benzene in the presence of a catalytic amount
[bmim][Br], this ratio decreases to ∼2 : 1. Under these
conditions, [bmim][Br] acts apparently as a phaseꢀtransꢀ
fer catalyst, which carries the anion of CHꢀacid 1a into
the organic phase. The effect of the imidazolium salt on
the transition state of the reaction follows from different
stereochemical outcomes of the reaction of phosphonate
1a with 3,7ꢀdimethyloctanal (4) carried out in benzene
and in the benzene—[bmim][Br] system (Table 2).
Similar regularities also hold in the reaction of ethyl
4ꢀdiethoxyphosphorylꢀ3ꢀmethylbutꢀ2ꢀenoate (1a) with
Table 1. Influence of the base on the yield and stereochemistry of dienoic ester 3 in various
solvents
a
Base
τ /h
The yield of 3 in
[bmim][PF6]
(%)
Ratio of 2E,4E to 2Z,4E stereoisomers
in diene 3
[bmim][PF6]
DMSOb
benzeneb
KOH
LiOH•H2O
[bmim][ОН]
2
6
6
58
48
52
3 : 2
3 : 2
3 : 2
7 : 3
4 : 1
—
44 : 56
3 : 2
—
c
c
a
τ is the reaction time.
b Data from Ref. 3.
c No data are available.
Table 2. Influence of the ionic liquid on the yield and stereochemistry of the diene ester 5 (hydroprene)
Base
Solvent
Catalyst
τ/h The yield of 5
Ratio of 2E,4E to 2Z,4E
isomers in diene 5
(%)
KOH
KOH
Benzene
Benzene
—
6
6
60
63
44 : 56*
65 : 35
[bmim][Br]
(0.1 equiv.)
—
LiOH•H2O
[bmim][PF6]
10
75
3 : 1
* Data from Ref. 4.

Synthesis of isoprenoids in ionic liquids
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 3, March, 2004
661
Table 3. Reaction conditions, product yield, and isomer ratio in dienoic ester 8
Base
Solvent
Catalyst
(equiv.)
τ/h
The yield of 8
Ratio of 2E,4E to 2Z,4E
isomers in diene 8
(%)
KOH
KOH
KOH
[bmim][ОН]
Benzene
Benzene
[bmim][PF6]
[bmim][PF6]
[bmim][Br] (0.1)
[bmim][Br] (1.0)
5
4
4
6
74
70
65
67
7 : 3
7 : 3
3 : 1
3 : 1
—
—
benzaldehyde (7) (Table 3). In this case, too, replaceꢀ
ment of the [bmim][PF6] ionic solvent by the benꢀ
zene—imidazolium salt system results in somewhat lower
ratio of the 2E,4E to 2Z,4E stereoisomers in the reaction
product 8. The increase in the amount of the imidazolium
salt [bmim][Br] from a catalytic (∼0.1 equiv.) to equimoꢀ
lar amount with respect to the reactants does not affect
noticeably the stereochemical outcome of the reaction.
portion of the 2E,4E isomer 9 is lower than that obtained
in the olefination in the solid КOH (2 equiv.)—benꢀ
n
zene—[Bu4 N][Br] (2 equiv.) system (the ion pair extracꢀ
tion method).4 The replacement of the 1ꢀbutylꢀ3ꢀmethylꢀ
imidazolium cation by the 1ꢀbutylꢀ2,3ꢀdimethylimidꢀ
azolium cation does not result either in a higher 2E,4Eꢀ to
2Z,4E ratio in product 9.
The Eꢀstereoselectivity of the reaction of phosphonate
1b with aldehyde 6 was somewhat increased by conductꢀ
ing the olefination directly in the medium of the 1ꢀbutylꢀ
3ꢀmethylimidazolium salts [bmim][PF6] or [bmim][BF4],
which are liquid under ordinary conditions. Irrespective
of the nature of the anion, the ratio of the 2E,4E to 2Z,4E
isomers in olefination product 9 was 3 : 1, which is
similar to the values attained in the solid КOH—benꢀ
n
zene—[Bu4 N][Br] (cat.) system.4
We studied the reaction of isopropyl 4ꢀdi(isopropꢀ
oxy)phosphorylꢀ3ꢀmethylbutꢀ2ꢀenoate (1b) with 3,7ꢀdiꢀ
methylꢀ7ꢀmethoxyoctanal (6) in most detail (Table 4).
The addition of the imidazolium salt [bmim][Br] to the
solid КOH—benzene system inverts again the reaction
stereochemistry, resulting in the predominant formation
of the 2Е,4Е isomer of compound 9. The ratio of 2E,4E
to 2Z,4E isomers remains the same, irrespective of
whether the system contains a catalytic or an equimolar
amount of the imidazolium salt, although an increase
in the amount of the catalyst results in a higher overall
yield of the olefination product 9. In both cases, the proꢀ
The moderate stereoselectivity of the reactions of alkyl
4ꢀdialkoxyphosphorylꢀ3ꢀmethylbutꢀ2ꢀenoates (1a,b) with
isoprenoid aldehydes carried out in the imidazolium
Table 4. Influence of the ionic liquid and reaction conditions on the yield and stereochemistry of diene ester 9
(methoprene)
Base
(equiv.)
Solvent
Catalyst
(equiv.)
τ/h
The yield of 9
Ratio of 2E,4E to 2Z,4E
isomers in diene 9
(%)
KOH (1.0)
KOH (1.0)
КОН (2.0)
KOH (1.0)
KOH (1.0)
LiOH•H2O (1.0)
KOH (1.0)
КОН (1.0)
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
[bmim][PF6]
[bmim][BF4]
—
2
3
3
8
8
8
6
6
61
79
85
72
81
68
77
75
30 : 70*
75 : 25*
93 : 7*
65 : 35
65 : 35
65 : 35
75 : 25
75 : 25
[Bu4nN][Br] (0.1)
[Bu4nN][Br] (2.0)
[bmim][Br] (0.1)
[bmim][Br] (1.0)
[bdmim][PF6] (1.0)
—
—
* Data from Ref. 4.

662
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 3, March, 2004
Zlotin et al.
n
salt—benzene system compared to the corresponding reꢀ
actions in the [Bu4 N][Br]—benzene system is apparently
the [bmim], [bdmim], and [Bu4 N] cations. Their optiꢀ
mized geometries thus obtained are shown in Fig. 1.
The averaged radii (r0) of the [bmim], [bdmim], and
n
due to the different geometric parameters of the [bmim],
n
n
[bdmim], and [Bu4 N] cations. The influence of the size
[Bu4 N] cations determined with account of the maxiꢀ
of the cation of the phaseꢀtransfer catalyst on the transiꢀ
tion state of olefination reaction has been hypothesized
previously.1 In order to verify this assumption, we carried
out quantumꢀchemical calculations for the geometry of
mum distances between the terminal atoms (L, H, and W )
using Eq. (1) were 2.6, 2.8, and 3.9 Å, respectively.
r0 ≈ (3HWL)1/3/4π
(1)
The agreement between the resulting r0 = 3.9 Å and
n
the Stokes radius of the [Bu4 N] cation in methanol deꢀ
a
termined experimentally13 (∼4.3 Å) may be regarded as
satisfactory, in view of the fact that the calculation did not
take into account the effect of the medium, which is
known to change somewhat the geometric parameters of
cations.14 Thus, of the three cations studied, the [Bu4 N]
cation has the largest radius, which markedly exceeds
those of [bmim] or [bdmim].
The results of calculations are consistent with the asꢀ
sumption that the ratio of the 2E,4E to 2Z,4E isomers in
the Horner—Emmons reaction products changes in parꢀ
allel with the linear dimensions of the cation in the phaseꢀ
transfer catalyst used. The shape of the cation (flattened
in the case of the [bmim] and [bdmim] cations13 and
H
H
C
H
C
C
N
H
W = 4.227
H
H
H
H = 1.773
N
n
H
C
C
H
L = 9.810
H
C
H
C
H
C
H
H
H
b
H
H
H
H
W = 4.841
C
C
N
H = 1.771
H
C
H
L = 10.169
H
H
n
threeꢀdimensional for [Bu4 N]) (see. Fig. 1) may also
H
C
N
H
C
H
C
H
exert a certain influence on the stereoselectivity. The
somewhat higher stereoselectivity of olefination when carꢀ
ried out directly in ionic liquids is apparently due to the
change in the medium polarity, which influences the geoꢀ
metric parameters of the transition state.14
C
H
H
C
C
H
H
H
The use of imidazolium salts with fluorinated anions
as the solvents has a number of advantages, in particular,
the ease of isolation of the products, avoidance of toxic
benzene in operation, and the possibility of recovery and
reuse of the ionic solvent. Dienoic esters 3, 5, 8, and 9
can be separated from nonvolatile liquid imidazolium salts,
[bmim][BF4] and [bmim][PF6], by direct distillation unꢀ
der reduced pressure (0.1—1.0 Torr). Ionic liquids are
easily recovered after the reaction by filtering from inorꢀ
ganic salts followed by washing with water (in the case of
[bmim][PF6], which is immiscible with water) and reꢀ
moval of volatile compounds (water, CHCl3) under reꢀ
duced pressure. The yield of ionic liquids is 89—95%. The
[bmim][BF4] and [bmim][PF6] salts recovered in this way
H
H
c
H
C
L = 8.811
W = 8.811
C
H
C
H
H
H
H
H
H
H
H
C
H
H
C
C
H
H
C
H
H
H
C
C
H
C
C
H
H
C
N
C
H
H
H
H
H
H = 3.139
C
H
H
H
H
1
are identical, according to the H, 13C, and 19F NMR
C
spectra to fresh ionic liquids7,9,10 and can be used in
olefination once again. An increase in the number of
"olefination—regeneration" cycles to 10 does not entail a
decrease in the yields or stereochemical purity of the
dienoic esters 3, 5, 8, and 9.
C
H
H
H
H
C
H
Thus, we studied for the first time the reaction of alkyl
4ꢀdialkoxyphosphorylꢀ3ꢀmethylbutꢀ2ꢀenoates 1a,b with
isoprenoid aldehydes and benzaldehyde in imidazolium
salts that are liquid under ordinary conditions and in
imidazolium salt—benzene systems. This reaction was
Fig. 1. Results of quantumꢀchemical calculations for the geomꢀ
etry of 1ꢀbutylꢀ3ꢀmethylimidazolium ([bmim]) (a), 1ꢀbutylꢀ2,3ꢀ
dimethylimidazolium ([bdmim]) (b), and tetrabutylammonium
([Bu4nN]) cations (c).

Synthesis of isoprenoids in ionic liquids
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 3, March, 2004
663
7.5 mmol) in water (2 mL). Water was evaporated in vacuo and
the residue was dissolved in MeOH (5 mL) and filtered. The
filtrate was concentrated, and [bmim][PF6] (4.25 g, 15 mmol)
was added to the residue, which represented imidazolium hyꢀ
droxide [bmim][OH].12 Then phosphonate 1a (1.30 g, 5.0 mmol)
and aldehyde 7 (0.53 g, 5.0 mmol) were added with vigorous
stirring. The reaction mixture was stirred for 6 h at 20 °C, and
product 8 was distilled off under reduced pressure.
The reactions were monitored and the isomeric composition
of the products was determined by GLC and 1H NMR spectroꢀ
scopy (based on the ratio of the signals for the methylene group
protons at C(3) and olefinic protons at C(2) in the stereoisomers
of 3, 5, 8, and 9).3,4 The two methods gave similar results. The
boiling points and the refractive indices of dienoic esters 3, 5, 8,
employed to synthesize a number of biologically active
substances, analogs of natural isoprenoids, including
dienoic ester 3, which is an efficient chemosterilant for
the arachnoid mite, and environmentally safe insecticides,
hydroprene 5 and methoprene 9, which are structural
analogs of insect juvenile hormones.15,16 The results obꢀ
tained can be used to develop stereoselective and enviꢀ
ronmentally safe methods for the deliberate synthesis of
natural products using ionic liquids as solvents and
catalysts.
Experimental
and 9 corresponded to published data: ethyl 3,7ꢀdimethyloctaꢀ
1
H NMR spectra were recorded on Bruker AMꢀ300
20
2,4ꢀdienoate (3), b.p. 125—128 °C (12 Torr), nD 1.4800 25
;
(300.13 МHz {1H}) and Bruker DRXꢀ500 (500.13 МHz {1H},
125.76 МHz {13C}, 470.4 МHz {19F}, 202.4 МHz {31P}) instruꢀ
ments in DMSOꢀd6 and acetoneꢀd6. The 1H, 13C, 19F, and
31Р NMR chemical shifts were referred to Me4Si, acetoneꢀd6,
CFCl3, and H3PO4, respectively. GLC analysis was carried out
on a LKhMꢀ80 chromatograph with a flame ionization detecꢀ
tor using N2 as the carrier gas and a 1.5×0.003 m glass colꢀ
umn with 5% SEꢀ30 or OVꢀ17 on Chromaton NꢀAWꢀDMCS.
Phosphonates 1a,b17 and imidazolium salts, [bmim][Br],8
[bmim][PF6],9 [bmim][BF4],10 and [bdmim][PF6],11 were synꢀ
thesized by known procedures.
The geometry of the 1ꢀbutylꢀ3ꢀmethylimidazolium and
1ꢀbutylꢀ2,3ꢀdimethylimidazolium cations was optimized using
the B3LYP hybrid functional18—20 in the standard 6—31G* baꢀ
sis set.21 The calculations were carried out using the Gaussian 98
program package.*22 The molecular structures and vibrations
were visualized using the MOLDEN graphics package.23 The
geometry of the tetrabutylammonium cation was optimized usꢀ
ing the PRIRODA program24 with the PBE functional in the
3z fullꢀelectron basis set.
Reaction of aldehydes 2, 4, 6, and 7 with phosphonates 1a,b
in the КOH/[bmim][PF6], КOH/[bmim][BF4], and LiOH•
•H2O/[bmim][PF6] systems (general procedure). The finely
ground base (7.5 mmol), phosphonate 1a or 1b (5.0 mmol), and
aldehyde 2, 4, 6, or 7 (5.0 mmol) were added successively with
vigorous stirring at 20 °C to an ionic liquid (15 mmol). The
reaction mixture was stirred at 20 °C for 2—10 h and products 3,
5, 8, and 9 were extracted with diethyl ether (4×10 mL) and
distilled in vacuo (0.1—12 Torr), or directly distilled off from the
ionic liquid under reduced pressure.
Reaction of aldehydes 4, 6, and 7 with phosphonates 1a,b in
the КOH/PhH/[bmim][Br] and LiOH•H2O/PhH/[bmim][PF6]
systems (general procedure). Phosphonate 1a or 1b (5.0 mmol)
and aldehyde 4, 6, or 7 (5.0 mmol) were added successively with
vigorous stirring to a suspension of powdered КOH (0.40 g,
7.5 mmol) and imidazolium salt (0.5—5.0 mmol) in benzene
(10 mL). The reaction mixture was stirred for 4—8 h at 20 °C
and filtered. The benzene solution was concentrated on a rotary
evaporator and compounds 5, 8, and 9 were distilled under
reduced pressure.
ethyl 3,7,11ꢀtrimethylundecaꢀ2,4ꢀdienoate 5 (hydroprene), b.p.
99—101 °C (0.1 Torr), nD20 1.4815 4; ethyl 3ꢀmethylꢀ5ꢀphenylꢀ
pentaꢀ2,4ꢀdienoate (8), b.p. 138—140 °C (0.8 Torr),
nD 1.5880 26; isopropyl 11ꢀmethoxyꢀ3,7,11ꢀtrimethylundecaꢀ
20
2,4ꢀdienoate (9) (methoprene), b.p. 144—146 °C (0.5 Torr),
20
nD 1.4835 4.
Recovery of [bmim][PF6]. The liquid remained after the
reaction and the product isolation was filtered to remove inorꢀ
ganic salts, washed with water (2×10 mL), and evacuated (2 Torr)
at 60 °C for 2 h to give a yellowish liquid identical, according to
1H, 31P, and 19F NMR spectra in acetoneꢀd6, to the freshly
prepared salt [bmim][PF6]. 1H NMR, δ: 0.93 (t, 3 H, J = 7.5 Hz);
1.36 (sext, 2 H, J = 7.5 Hz); 1.89 (quint, 2 H, J = 7.5 Hz); 4.00
(s, 3 H); 4.30 (t, 2 H, J = 7.5 Hz); 7.62 (d, 1 H, J = 1.8 Hz); 7.68
(d, 1 H, J = 1.8 Hz); 8.82 (s, 1 H). 31P NMR, δ: –142.4 (sept,
1
1JP,F = 708 Hz). 19F NMR, δ: –71.0 (d, JP,F = 708 Hz). The
yield of recovered [bmim][PF6] was 89—94%.
Recovery of [bmim][BF4]. The salt left after the reaction and
the product isolation was diluted with CHCl3 (10 mL) and the
resulting solution was filtered to remove inorganic salts and
dried with MgSO4. The solvent was evaporated in vacuo and the
remaining oil was kept for 2 h at 60 °C (2 Torr) to give a
1
yellowish liquid identical, according to H, 13C, and 19F NMR
spectra in acetoneꢀd6, to the freshly prepared salt [bmim][BF4].
1H NMR, δ: 0.93 (t, 3 H, J = 7.5 Hz); 1.36 (sext, 2 H, J =
7.5 Hz); 1.89 (quint, 2 H, J = 7.5 Hz); 4.00 (s, 3 H); 4.30 (t, 2 H,
J = 7.5 Hz); 7.62 (d, 1 H, J = 1.8 Hz); 7.68 (d, 1 H, J = 1.8 Hz);
8.82 (s, 1 H). 13C NMR, δ: 13.73 (CH3); 19.95 (CH2); 32.75
(CH2); 36.52 (CH2); 50.09 (N—CH3); 123.36 (CH); 124.68
(CH); 137.68 (CH). 19F NMR, δ: –150.5. The yield of recovꢀ
ered [bmim][BF4] was 90—95%.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 03ꢀ03ꢀ
32659), the Russian Academy of Sciences (the Fundaꢀ
mental Research Program of the Presidium of the RAS),
and President of the Russian Federation (Program for
the Support of Leading Scientific Schools, grant
NSh 1803.2003.3).
Reaction of aldehyde 7 with phosphonate 1a in the
[bmim][OH]/[bmim][PF6] system. Powdered КOH (0.40 g,
7.5 mmol) was added to a solution of [bmim][Br] (1.60 g,
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Received December 30, 2003;
in revised form February 20, 2004