ISSN 09655441, Petroleum Chemistry, 2012, Vol. 52, No. 4, pp. 261–266. © Pleiades Publishing, Ltd., 2012. Original Russian Text © R.I. Khusnutdinov, A.R. Bayguzina, L.I. Gallyamova, U.M. Dzhemilev, 2012, published in Neftekhimiya, 2012, Vol. 52, No. 4, pp. 292–298.
A Novel Method for Synthesis of Benzyl Alkyl Ethers Using VanadiumBased Metal Complex Catalysts R. I. Khusnutdinov, A. R. Bayguzina, L. I. Gallyamova, and U. M. Dzhemilev Institute of Petroleum Chemistry and Catalysis, Russian Academy of Sciences, pr. Oktyabrya 141, Ufa, 450075 Russia email:
[email protected] Received January 16, 2012
Abstract—A novel method has been developed for the synthesis of benzyl alkyl ethers in 25–85% yields via the reaction of toluene with alcohols in a CCl4 medium catalyzed by Et3Nactivated VO(acac)2. DOI: 10.1134/S0965544112040044
Benzyl alkyl ethers find wide application in per fumery and food industry as fragrances and food addi tives. Typically they are prepared by the Williamson reaction between alkali metal alkoxides and benzyl bromide [1] or Ag2O [2]. The synthesis of ethers from substrates that are unstable in an alkaline medium is performed with benzyl trifluoroacetimidate, which allows the reaction to be carried out in an acidic medium [3]. When 2benzyloxy1methylpyridinium triflate is used as a benzylating agent, the successful synthesis of benzyl alkyl ethers can be accomplished in a neutral medium [4]; they can be also prepared from silyl ethers and aromatic aldehydes in the presence of tri ethylsilane and catalytic amounts of FeCl3 [5]. Sirke cioglu et al. [6] reported the synthesis of benzyl alkyl ethers by the Cu(acac)2catalyzed reaction of benzyl chloride with structurally different alcohols. The goal of the present work was to develop a novel efficient synthetic method for benzyl alkyl ethers by the reaction of toluene with alcohols in a CCl4 medium under the action of metal complex catalysts. EXPERIMENTAL NMR spectra were recorded on a Bruker Avance 400 (400.13 and 100.62 MHz, respectively) spectrom eter in CDCl3; the chemical shifts (δ) are given in ppm relative to TMS. Mass spectra were recorded on a Shi madzu GCMSQP2010Plus gas chromatograph/mass spectrometer (SPB5 capillary column, 30 m × 0.25 mm; carrier gas, helium; temperature program ming from 40°C to 300oC at a rate of 8oC min–1; evap orator temperature, 280°C; ion source temperature. 200°C; ionization energy—70 eV). The chromato graphic analysis was performed on a Shimadzu GC 9A instrument (column dimensions of 2 m × 3 mm; stationary phase, silicone SE30 (5%) supported on Chromaton NAWHMDS, temperature program
ming mode, from 50 to 270°C at a rate of 8оC/min; carrier gas, helium (47 mL/min)). The reactants were commercially available metha nol, ethanol, propanol1, propanol2, butanol1, pentanol1, hexanol1, heptanol1, octanol1, unde canol1, cyclopentanol, cyclohexanol, benzyl alcohol, toluene, ССl4, CHCl3, СHBr3, CBrCl3, formamide, pyridine, and acetonitrile, which were distilled prior to use. The catalysts V2O5, VO2, V2O3, VO(acac)2, VCl3, and VCl4 were dried in a vacuum desiccator; СBr4, 2,2'bipyridyl, 4,4'bipyridyl, and triphenylphosphine (Acros) were recrystallized from benzene and ethanol prior to use. The reactions were carried out in a glass ampoule (V = 10 mL) placed in a stainless steel microautoclave (V = 17 mL) with continuous stirring and controlled heating. General Procedure for Synthesis of Benzyl Alkyl Ethers (1, 6–18) An ampoule was charged under argon with 0.0058 g (0.022 mmol) of VO(acac)2, 0.01 mL (0.077 mmol) of Et3N, 0.2 mL (2.08 mmol) of CCl4, and 8.7 mmol (0.28 g of СН3OH, 0.4 g of С2Н5OH, 0.52 g of n С3Н7OH, 0.52 g of isoС3Н7OH, 0.64 g of nС4Н9OH, 0.77 g of nС5Н11OH, 0.89 g of nС6Н13OH, 1.01 g of n С7Н15OH, 1.13 g of nС8Н17OH, 1.5 g of nС11Н23OH, 0.94 g of PhCH2OH, 0.75 g of cycloC5H9OH, or 0.87 g of cycloC6H11OH) (or 34.7 mmol (2.6 g) in the case of nС4Н9OH). The sealed ampoule was heated in the autoclave at 175оС for 14 h in the case of СН3OH, С2Н5OH, nС3Н7OH, isoС3Н7OH, nС4Н9OH, nС5Н11OH, nС6Н13OH, nС7Н15OH, nС8Н17OH, or n С11Н23OH; 20 h in the case of PhCH2OH; and 10 h in the case of cycloC5H9OH or cycloC6H11OH with vigorous stirring. After the reaction completion, the autoclave was cooled to 20оС, the reaction mixture was neutralized with a 10% Na2CO3 aqueous solution
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(stirring for 1h), the organic layer was extracted with chloroform, and the extract was filtered through a pad of silica gel (2 g). The unreacted toluene, light ethers, and chloroform were removed on a rotor evaporator. The residue was analyzed by GLC using decane as an internal standard. To obtain chromatographically pure samples, to determine the yield, and to identify the resulting ben zyl alkyl ethers, the experiments were performed with a tenfold greater charge. An ampoule (50 mL) was charged under argon with 0.058 g (0.022 mmol) of VO(acac)2, 0.1 mL (0.077 mmol) of Et3N, 2 mL (2.08 mmol) of CCl4, 8.7 mmol (2.8 g of СН3OH, 4 g of С2Н5OH, 5.2 g of nС3Н7OH, 5.2 g of isoС3Н7OH, 6.4 g of nС4Н9OH, 7.7 g of n С5Н11OH, 8.9 g of nС6Н13OH, 10.1 g of nС7Н15OH, 11.3 g of nС8Н17OH, 15 g of nС11Н23OH, 9.4 g of PhCH2OH, 7.5 g of cycloC5H9OH, or 8.7 g of cyclo C6H11OH) (or 34.7 mmol (26 g) in the case of n С4Н9OH). The sealed ampoule was placed in the autoclave (V = 100 mL), the autoclave was tightly sealed and heated at 175оС for 14 h in the case of СН3OH, С2Н5OH, nС3Н7OH, isoС3Н7OH, n С4Н9OH, nС5Н11OH, nС6Н13OH, nС7Н15OH, n С8Н17OH, or nС11Н23OH; 20 h in the case of PhCH2OH; and 10 h in the case of cycloC5H9OH or cycloC6H11OH, respectively) under continuous stir ring. After completion of the reaction, the autoclave was cooled to 20оС, the ampoule was unsealed, the reaction mixture was neutralized with 10% Na2CO3 aqueous solution (stirring with a magnetic stirrer for 1 h), the organic layer was extracted with chloroform, and the extract was filtered through a pad of silica gel (20 g). The unreacted toluene, light ethers, and chlo roform were preliminary evaporated on a rotor evapo rator. Benzyl chloride, higher dialkyl ethers, and ben zyl alkyl ethers were isolated by vacuum distillation. The structure of the resulting benzyl alkyl ethers was confirmed by the spectral data and by comparing with the known samples and reference data: benzyl methyl ether, 1 (yield 85%) [7], benzyl ethyl ether, 6 (yield 26%), benzyl propyl ether, 7 (yield 27%) [8], benzyl 2propyl ether, 8 (yield 32%) [9], benzyl butyl ether, 9 (yield 34%) [7], benzyl amyl ether, 10 (yield 24%) [10], dibenzyl ether, 15 (yield 62%) [11– 12], benzyl cyclohexyl ether, 18 (yield 64%) [13]. Benzyl hexyl ether, 11. Yield 52%, bp 106– 107°C/6 torr. 13C NMR (CDCl3, δ, ppm): 138.74 (C1), 128.34 (C3, C5), 127.59 (C2, C6), 127.45 (C4); 72.90 (C7), 70.54 (C8), 29.91 (C9), 28.78 (C10), 25.87 (C11), 22.78 (C12), 14.14 (C13). 1H NMR (CDCl3, δ, ppm): 1.04 (3H, t, 3JHH = 7.2 Hz, СН3), 1.35⎯1.80 m (8H, СH2(СH2)4СH3), 3.57 t (2H, 3JHH = 6.4 Hz, OСН2CH2), 4.54s (2Н, СH2O), 7.30–7.50 m (5H, Ar, CH). Found (%): C, 81.41; H, 10.37; O, 8.22. Calculated for C13H20O (%): C, 81.20; H, 10.48; O, 8.32.
Benzyl heptyl ether, 12. Yield 25%, bp 99–100°C/2 torr. 13C NMR (CDCl3, δ, ppm): 138.78 (C1), 128.34 (C3, C5), 127.60 (C2, C6), 127.45 (C4); 72.88 (C7), 70.55 (C8), 31.88 (C9), 29.84 (C10), 29.21 (C11), 26.22 (C12), 22.66 (C13), 14.11 (C14). 1H NMR (CDCl3, δ, ppm): 0.94 t (3H, 3JHH = 6.8 Hz, СН3), 1.25–1.80 m (10H, СH2(СH2)5СH3), 3.52 t (2H, 3JHH = 6.8 Hz, OСН2CH2), 4.55 s (2Н, СH2O), 7.20–7.45 (5H, Ar, CH). Found (%): C, 81.63; H, 10.86; O, 7.53. Calculated for C14H22O (%): C, 81.50; H, 10.75; O, 7.76. Benzyl octyl ether, 13. Yield 69%, bp 88–90°C/0.5 torr. 13C NMR (CDCl3, δ, ppm): 138.79 (C1), 128.40 (C3, C5), 127.7 (C2, C6), 127.59 (C4); 72.88 (C 7), 70.54 (C8), 31.91 (C9), 30.00 (C10), 29.86 (C 11), 29.52 (C12), 28.73 (C13), 25.08 (C14), 14.00 (C15). 1H NMR (CDCl3, δ, ppm): 0.94 t (3H, 3JHH = 6.8 Hz, СН3), 1.35–1.80 m (12H, СH2(СH2)6СH3), 3.52 t (2H, 3JHH = 6.4 Hz, OСН2CH2), 4.55 s (2Н, СH2O), 7.20–7.50 m (5H, Ar, CH). Found (%): C, 81.52; H, 10.88; O, 7.60. Calculated for C15H24O (%): C, 81.76; H, 10.98; O, 7.26. Benzyl undecyl ether, 14. Yield 61%, bp 105– 107°C/0.2 torr. 13C NMR (CDCl3, δ, ppm): 138.72 (C1), 128.31 (C3, C5), 127.60 (C2, C6), 127.44 (C4); 72.84 (C7), 70.54 (C8), 31.93 (C9), 29.78 (C10), 29.60 (C11), 29.50 (C12), 29.48 (C13), 29.35 (C14), 28.91 (C15), 28.61 (C16), 22.69 (C 17), 14.10 (C18). 1H NMR (CDCl3, δ, ppm): 0.94 (3H, t, 3JHH = 7.2 Hz, СН3), 1.35–1.80 m (18H, СH2(СH2)6СH3), 3.64 t (2H, 3JHH = 6.8 Hz, OСН2CH2), 4.52 s (2Н, СH2O), 7.20–7.50 m (5H, Ar, CH). Found (%): C, 82.54; H, 11.45; O, 6.01. Cal culated for C18H30O (%): C, 82.38; H, 11.52; O, 6.10. Benzyl cyclopentyl ether, 17. Yield 69%, bp 116– 117°C/10 torr. 13C NMR (CDCl3, δ, ppm): 138.29 (C1), 128.42 (C3, C5), 127.80 (C2, C6), 127.35 (C4); 80.90 (C8), 70.71 (C7), 32.32 (C9, C12), 23.61 (C10, C11). 1H NMR (CDCl3, δ, ppm): 1.2– 1.8 m (8H, CH2), 3.95–4.08 m (1H, CH), 4.59 s (2H, CH2), 7.10–7.60 m (5H, Ar, CH). Found (%): C, 81.79; H, 9.23; O, 8.98. Calculated for C12H16O (%): C, 81.77; H, 9.15; O, 9.08. RESULTS AND DISCUSSION Preliminary experiments showed that benzyl methyl ether 1, a valuable fragrance with a fruit smell of ilangilang and green hyacinth flowers, can be syn thesized by reacting toluene with methanol in a ССl4 medium in the presence of the following vanadium compounds: V2O5, VO2, V2O3, VCl3, VCl4, or VO(acac)2, of which VO(acac)2 is the best (the reaction is too sen sitive to the moisture content). As ligands, the follow ing compounds were also tested: formamide, pyridine, 2,2'bipyridyl, 4,4'bipyridyl, acetonitrile, and triphe nylphosphine, which are inferior in activity to triethy lamine (see table). PETROLEUM CHEMISTRY
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A NOVEL METHOD FOR SYNTHESIS OF BENZYL ALKYL ETHERS
263
Effect of the catalyst nature, ligand nature, and reaction time on the toluene conversion and product yields in the reaction of toluene with CCl4 and MeOH (175°C)
diarylmethanes*
0.3
0.5
3
8
2
1
0
0
2.4
0.3
0.5
0.1
19
4
1
1
2
0
10
6.5
1.5
2
0
40
4
32
3
1
0
0
Toluene conversion,%
1
V2O3
–
4
15
0.4
2
VO2
–
''
16
1
3
V2O5
–
''
4
4
VCl3
–
''
27
0
5
VCl4
–
''
20
6
VO(acac)2
–
''
0.3
2.8 12 0.4
BnOH
Time, h
BnCl
Ligand
BnOMe
Catalyst
PhCHO
Run no.
PhCO2Me
Yields of products, %
7
''
HCONH2
''
0
0
0
0
0
0
0
8
''
2,2' bipyridyl
''
9
1
4
3
0
0
1
9
''
4,4' bipyridyl
''
10
0.5
6
1
0.5
1
1
10
''
CH3CN
''
47
6
31
3
1
3
3
11
''
PPh3
''
100
26
39
12
2
11
10
12
''
pyridine
''
12
2
4
4
3
0
13
''
Et3N
''
47
2
42
2
1
0
0
''
1.5
32
0.6
29
2
0.4
0
0
14
VO(acac)2
15
''
''
2
39
1
35
2.5
0.5
0
0
16
''
''
4
47
2
42
2
1
0
0
17
''
''
6
55
5
48
1
1
0
0
18
''
''
7
57
6.5
49
1
0.5
0
0
19
''
''
9
65
10
52
2
1
0
0
20
''
''
10
74
10
61
2
1
0
0
21
''
''
12
95
10
80
3
2
0
0
22
''
''
14
100
10
85
3
2
0
0
* 2methyldiphenylmethane, 3methyldiphenylmethane, 4methyldiphenylmethane (5 : 1 : 5).
Among the tested halogenated methanes: ССl4, CHCl3, СHBr3, CBr4, and CBrCl3, the reaction pro ceeds best of all with carbon tetrachloride. Chloro form and bromoform appeared to be inactive in this reaction, and the use of CBr4 or CBrCl3 made the pro cess nonselective despite a high conversion of the reac tant toluene (47% and 59% for 4 h at 175оС, respec tively). Thus, the reaction of toluene with CBr4 and MeOH in the presence of the VO(acac)2–Et3N cata lytic system affords benzyl methyl ether (4%), benzyl bromide (3%), methyl benzoate (20%), benzyl alcohol PETROLEUM CHEMISTRY
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(8%), benzaldehyde (8%), and diarylmethanes in the ratio of 2methyldiphenylmethane : 3methyldiphe nylmethane : 4methyldiphenylmethane = 5 : 1 : 5 (4%) [14, 15], as well as CHBr3, MeOMe, HCO2Me, and MeBr. The analogous reaction with CBrCl3 led to the formation of a more complex product mixture consisting of benzyl methyl ether (12%), benzyl bro mide (3%), benzyl chloride (2%), benzaldehyde (11%), methyl benzoate (20%), benzyl alcohol (6%), and diarylmethanes in the 2methyldiphenylmethane : 3methyldiphenylmethane : 4methyldiphenyl
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methane ratio of 3 : 1 : 3 (5%), as well as CHBrCl2, CHBr2Cl, CHBr3, C2Cl4, C2Cl6, MeOMe, HCO2Me, MeBr, and MeCl.
PhMe + MeOH + CCl4
VO(acac)2 ⎯Et3N 175°C, 14 h –Me2O
The greatest yield of benzyl methyl ether 1 (85% over 14 h) is achieved using triethylamineactivated VO(acac)2 as a catalyst.
BnOMe + BnCl + PhCHO + BnOH 1 2 3 4 85% 3% 10% 2%
VO(acac)2 : Et3N : toluene : MeOH : CCl4 = 1 : 5 : 100 : 400 : 100. Scheme 1.
Along with compounds 1–4, the reaction mix ture also contained the following byproducts: chloroform, HCl, water, dimethyl ether, formalde
hyde dimethyl acetal, methyl formate, which are formed by the following scheme according to pub lished data [16, 17]: H+, MeOH
MeOH + CCl4
VO(acac)2 –CHCl3
MeOH 5
–HCl
CH2O
MeOCl
CH2(OMe)2 HCO2Me.
Scheme 2.
A key byproduct affecting the reaction course is methyl hypochlorite, which was also detected in our experiments (iodometric titration, concentration of 0.03–0.05 mg/mL). Taking into account the forma tion of methyl hypochlorite, we first assumed the reac tion scheme suggesting toluene oxidation with MeOCl to the final product. VO(acac)2
MeOH + CCl4 PhMe + MeOCl
tetrachloride by the action of VO(acac)2 to give benzyl chloride, which undergoes methanolysis at the final stage.
PhMe + CCl4
[V] –CHCl3
+CH3OH, [V] –HCl
BnCl 2 Scheme 4.
BnOMe. 1
MeOCl + CHCl3
VO(acac)2 175°C, 6 h –HCl
BnOMe. 1
Scheme 3.
However, since benzyl chloride 2 and chloroform have been found in reaction mixture, the most likely scheme of the formation of ether 1 seems to involve two steps, toluene is initially chlorinated with carbon
BnCl + MeOH 2
This assumption is supported by the results of experiments with an authentic sample of benzyl chlo ride 2, which transforms into benzyl methyl ether 1 with a quantitative yield under the reaction condi tions; when the reaction is run with an admixture of carbon tetrachloride ([VO(acac)2] : [BnCl] : [MeOH] : [CCl4] = 1 : 100 : 400 : 100), the yield of benzyl methyl ether makes 91%.
175°C, 6 h conv. 100% CCl4 175°C, 6 h conv. 91%
VO(acac)2–Et3N
BnOMe 100% 1 BnOMe 91%. 1
Scheme 5.
Benzaldehyde 3 detected in a small amount (10%) in the reaction mixture (Table 1, run 22) is likely to
result from the benzyl alcohol oxidation mediated by CCl4 according to the following scheme:
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A NOVEL METHOD FOR SYNTHESIS OF BENZYL ALKYL ETHERS 2MeOH PhMe
CCl4
BnCl 2
HCl
H2O + (Me)2O CCl
H2O
4 BnCl BnOCl 4 5 Scheme 6.
We performed a kinetic study of the reaction of tol uene with CCl4 and methanol in the presence of the VO(acac)2–Et3N catalytic system. As can be seen from the data presented, the amount of benzyl chloride in the reaction products does not exceed 3% for a reac tion time of 1.5–14 h (see table). The reaction is common in character for the alco hol series: ethanol, propanol1, propanol2, butanol 1, pentanol1, hexanol1, heptanol1, octanol1, and PhMe + ROH + CCl4
265
[V] –HCl
PhCHO. 3
undecanol1 enter this reaction. The yields of the cor responding ethers 6–14 are 25–69%. It is noteworthy that as the length of the alkyl radical in the alcohol molecule increases, the yield of benzyl alkyl ether increases, a fact that can be explained by the ease of formation of homoethers from lower alcohols and their active oxidation with CCl4 into the correspond ing aldehydes and esters, which are detected indeed in small amounts in the reaction mixture. VO(acac)2–Et3N 175°C, 14 h –ROR
BnOR. 1–14
R = C2H5 nC3H7
(6) 26% (7) 27%
iC3H7
(8) 32%
nC4H9
(9) 34%
nC5H11 (10) 24% nC6H13 nC7H15 nC8H17 nC11H23 Scheme 7.
Benzyl butyl ether 9, which has a fruit smell is the most valuable in the series of benzyl alkyl ethers. It is allowed for use in many countries as a flavor for food products: drinks, desserts, baked goods, ice cream, and ice. Therefore, we carried out an additional study to find the conditions that would facilitate increasing the yield of benzyl butyl ether. In particular, the reac tion selectivity for benzyl butyl ether can be enhanced by increasing the concentration of nС4Н9OH, with the reaction time being reduced to 10 h. Under the optimal conditions: 175оС, 10 h, and a catalyst to reactants ratio of [VO(acac)2] : [Et3N] : [tol uene] : [СCl4] : [nС4Н9OH] = 1 : 5 : 100 : 100 : 1600, BhOH + PhOH + CCl4
VO(acac)2–Et3N 175°C, 20 h toluene conversion 100%
(11) (12) (13) (14)
52% 25% 69% 61%
toluene transforms into benzyl butyl ether 9 with a yield of 67% at a toluene conversion of 69%. When benzyl chloride is used instead of toluene as a reactant (at the catalyst to reactants ratio of [VO(acac)2] : [Et3N] : [benzyl chloride] : [n С4Н9OH] = 1 : 5 : 100 : 400) at 175°С, the reaction time reduces to 5 h, but the yield of benzyl butyl ether 9 makes ~100% despite this fact. The above reaction with toluene is characteristic of benzyl alcohol. The main product of the reaction is dibenzyl ether 15 (53%). At the same time, a marked amount of the alcohol is oxidized to benzaldehyde 3 (11%) and undergoes substitution chlorination to convert into benzyl chloride 2 (30%). Bn2O + BnCl + PhCHO 15 2 3
VO(acac)2 : Et3N : toluene : BnOH : CCl4 = 1 : 5 : 100 : 400 : 100 VO(acac)2 : Et3N : toluene : BnOH : CCl4 = 1 : 5 : 100 : 800 : 100 Scheme 8. PETROLEUM CHEMISTRY
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[4.2 : 2.5 : 1] [20 : 10 : 1]
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As the benzyl alcohol concentration increased rel ative to that of toluene ([VO(acac)2] : [Et3N] : [tolu ene] : [СCl4] : [BnOH] = 1 : 5 : 100 : 100 : 800) the yield of dibenzyl ether 15 reached 62%, and the tolu ene conversion was complete.
PhMe + (CH2)n
OH
The analogous reaction of toluene with cyclopen tanol and cyclohexanol led to the production of benzyl cyclopentyl 17 and benzyl cyclohexyl 18 ethers in 64 and 69 % yields, respectively.
CCl4, VO(acac)2, Et3N 175°C, 10 h
Bn
O
n = 2, 3
n = 2 (17) 69%
VO(acac)2 : Et3N : toluene : ROH : CCl4 = 1 : 5 : 100 : 400–1600 : 100 Scheme 9.
Thus, the reaction under study offers a simple route for the synthesis of benzyl alkyl ethers from available reagents: toluene, CCl4, and alcohols. ACKNOWLEDGMENTS This work was supported by the Russian Founda tion for Basic Research and the Government of Republic of Bashkortostan, RFBR project Povolzh’e 120397019. REFERENCES 1. S. Czernecki, C. Georgoulis, C. Provelenghiou, and G. Fusey Tetrahedron Lett. 17, 3535 (1976). 2. A. Bouzide and G. Sauve, Tetrahedron Lett. 38, 5945 (1997). 3. P. R. Skaanderup, C. S. Poulsen, L. Hyldtoft, et al., Synthesis, No. 12, 1721. 4. K. W. C. Poon and G. B. Dudley, J. Org. Chem. 71, 3923 (2006). 5. K. Iwanami, K. Yano, and T. Oriyama, Synthesis, No. 16, 2669 (2005). 6. O. Sirkecioglu, B. Karliga, and N. Talinli, Tetrahedron Lett. 44, 8483 (2003).
(CH2)n
n = 2 (17) 64%
7. S. A. Voitkevich, 865 Fragrances for Perfumery and Household Chemistry (Pishchevaya promyshlennost’, Moscow, 1994) [in Russian]. 8. W. J. Monacelli and G. F. Hennion, J. Am. Chem. Soc. 63, 1722 (1941). 9. W. T. Olson, H. F. Hipsher, C. M. Buess, I. A. Good man, I. Hart, J. H. Lamneck, L. C. Gibbons, J. Am. Chem. Soc. 69, 2451 (1947). 10. F. C. Whitmore and D. P. Langlois, J. Am. Chem. Soc. 55, 1518 (1933). 11. S. Kim, K. Chung, and S. Yang, J. Org. Chem. 52, 3917 (1987). 12. The Aldrich Catalog/Handbook of Fine Chemicals; (Ald rich, Milwaukee, 2007⎯2008). 13. M. B. Sassaman, K. D. Kotian, G. K. S. Prakash, and G. A. Olah, J. Org. Chem. 52, 4314 (1987). 14. R. I. Khusnutdinov, N. A. Shchadneva, A. R. Baiguz ina, Yu. Yu. Lavrent’eva, R. Yu. Burangulova, U. M. Dzhemilev, Pet. Chem. 44, 265 (2004). 15. S. Meyerson, H. Drews, and E. K. Fields, J. Am. Chem. Soc. 86, 4964 (1964). 16. R. I. Khusnutdinov, N. A. Shchadneva, A. R. Bayguz ina, et al., ARKIVOC XI, 53 (2004). 17. R. I. Khusnutdinov, N. A. Shchadneva, R. Yu. Buran gulova, et al., Russ. J. Org. Chem. 42, 1615 (2006)
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