Carbonylation of C7-C8 cycloalkanes leading to individual tertiary carbonyl-containing compounds

Article abstract of DOI:10.1016/S0040-4039(00)01761-5

Carbonylation of cycloheptane, methylcyclohexane, cyclooctane and ethylcyclohexane by CO in the presence of CBr₄·2AlBr₃ at -40°C and 1 atm was performed with good yields and selectivities. Individual esters of tertiary carboxylic aci

Full text of DOI:10.1016/S0040-4039(00)01761-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 9903–9907
Carbonylation of C7ꢀC8 cycloalkanes leading to individual
tertiary carbonyl-containing compounds
Irena Akhrem,* Lyudmila Afanas’eva, Pavel Petrovskii, Sergei Vitt and
Alexander Orlinkov
A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilova St.,
117813 Moscow, Russia
Received 28 June 2000; accepted 4 October 2000
Abstract
Carbonylation of cycloheptane, methylcyclohexane, cyclooctane and ethylcyclohexane by CO in the
presence of CBr4·2AlBr3 at −40°C and 1 atm was performed with good yields and selectivities. Individual
esters of tertiary carboxylic acids of the cyclohexane series were the products of these cycloalkane
carbonylations. © 2000 Elsevier Science Ltd. All rights reserved.
Selective functionalisation of alkanes and cycloalkanes is a topic of current interest.1 One-pot
reactions of saturated hydrocarbons with CO are of obvious potential. It has been reported that
insertion of CO into unactivated CꢀH bonds may be achieved under the action of transition
metals, Lewis and aprotic superacids and radical species.1a,b,2 Selectivities of alkane
(cycloalkane) transformations are known to decrease with the increase of hydrocarbon chain
length. This effect is caused by the increase in the number of CꢀH bonds of close reactivities for
the higher homologues. In addition, long chain carbocations produced in the course of
electrophilic transformations of alkanes and cycloalkanes are more liable to fragment than their
lower homologues.
Our approach to selective functionalisations of alkanes and cycloalkanes is based on the
application of superelectrophiles capable of effective generation of carbocations from alkanes
and cycloalkanes at low temperatures.3 Under these conditions, side reactions such as cracking
and subsequent transformations of functionalised products should be largely suppressed.
Besides, low temperatures favour the formation of branched products rather than their linear
isomers.4 This paper reports the first examples of carbonylation of cycloheptane, cyclooctane
and ethylcyclohexane. It is also noteworthy that the first selective electrophilic reaction of
methylcyclohexane with CO was achieved under the action of CBr4·2AlBr3 in the absence of any
other additives.
* Corresponding author. E-mail: cmoc@ineos.ac.ru
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)01761-5

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Cycloheptane reacts with CO in the presence of CBr4·2AlBr3 at −40°C and 1 atm for 2 h to
i
give (after treatment with PrOH) ester 1 as the sole carbonyl-containing product in 82% yield
(Table 1).5 Under similar conditions, methylcyclohexane behaves analogously to afford ester 1
in a similar yield.
Table 1
Carbonylation of cycloalkanes C7ꢀC8 with CO (1 atm) initiated by CBr4·2AlBr3 (E) in CH2Br2

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Both cyclooctane and ethylcyclohexane also react with CO in the presence of CBr4·2AlBr3 in
CH2Br2 at −40°C and 1 atm affording ester 2 as a sole carbonyl-containing product in 67–70%
yield after 0.5–1 h.
1
The structures of 1 and 2 were proved by H and 13C NMR and mass spectra.5 Isomeric
bromides cyclo-C7H13Br were formed as by-products in the reactions of cycloheptane or
methylcyclohexane, while cyclo-C8H15Br and small amounts of C8H14 were found in the
reactions of cyclooctane or ethylcyclohexane. Yields of these bromides are 10–30% based on
CBr4·2AlBr3, depending on the experimental conditions. During the course of these reactions,
CBr4 is converted completely into its reduced product CHBr3.
At −20°C ester 1 is also formed selectively as a sole carbonyl-containing product from
cycloheptane or methylcyclohexane carbonylation. However, under the same conditions (at
−20°C) the reaction of cyclooctane or ethylcyclohexane with CO occurred non-selectively
affording the mixture of the four isomeric esters, cyclo-C8H15COOPri (2+3a), in the ratio of
:4:2:4:1 with the isomer 2 being the minor component.
Semiempirical quantum-chemical calculations by the PM3 method revealed that cyclo-
+
EtC6H10 (2%) is the most stable cation among the isomeric tertiary cations cyclo-C8H15+. Cation
+
2% (152.6 kcal/mol) is 2.1 kcal/mol more stable than any of the isomeric tertiary cyclo-Me2C6H9
(3%) cations of equal stability (150.5 kcal/mol). As a result, the accumulation of the most stable
2% cation (and hence the formation of acyl cation 2%% and finally ester 2) should occur. At the
same time, the stabilities of acyl cations RCO+ are known to fall down with the increase of the
stabilities of the corresponding R+ cation.6 Therefore, decarbonylation of 2%% proceeds more
easily than the similar process for 3%% and the ester 2, which is formed exclusively upon the
carbonylation at −40°C, becomes a minor component of the carbonylation products at −20°C.

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The reaction of cyclooctane at −40°C and 30 atm CO also occurs non-selectively to result in
the isomeric mixture of esters qualitatively similar to that formed in the reaction at −20°C.
However, at −40°C the percentage of 2 increases by 2–2.5 times. The decrease in carbonylation
selectivity with the increase of CO pressure has been previously reported.7 Obviously, in the
presence of excess CO all carbocations generated in the system are trapped as acylium ions,
while the most stable carbocations are carbonylated if CO is deficient.
Isomerisations of cycloalkanes accompanied by the ring contraction is well documented.8 In
particular, it was observed9 that under comparable conditions cycloheptane is quantitatively
converted into methylcyclohexane, while cyclooctane furnished a mixture of 90% of ethylcyclo-
hexane and 10% of isomeric dimethylcyclohexanes, and the relative rates for these reactions were
evaluated as 3:2. To the best of our knowledge, the carbonylations of cycloheptane, cyclooctane
and ethylcyclohexane have not been described previously. The reaction of methylcyclohexane
with CO in the HFꢀSbF5 medium was reported2g to result in a mixture of 90% of isomeric
cyclo-Me2C6H9COOH and 10% of tertiary 1-methylcyclohexyl carboxylic acid. The carbonyla-
tion of methylcyclohexane by CO in 98% H2SO4 (or BF3ꢀH2O) in the presence of Cu or Ag salts
as the metallocarbonyl sources and olefins or alcohols as carbocation precursors, was reported
to give tertiary MeC6H10COOH in 20–70% yield.10 The drawback of this method is the necessity
to employ both the Cu (or Ag) salts and olefins or alcohols. As a result, besides the desired
product MeC6H10COOH, the carbonylation products derived from the olefin (or alcohol) are
formed in comparable amounts.
In conclusion, the use of the polyhalomethane based superelectrophilic systems allows
selective functionalisation by CO for the cycloalkanes C7ꢀC8. Thus, the set of saturated
hydrocarbons susceptible to the selective carbonylation is broadened to a substantial extent.
Acknowledgements
This work was supported by the Russian Foundation of Basic Research (grant no. 99-03-
33006). The authors express their thanks to Dr. A. L. Chistyakov for quantum-chemical
calculations.
References
1. (a) Olah G. A.; Prakash G. K. S. In The Chemistry of Alkanes and Cycloalkanes, Part 13; Patai, S.; Rappoport,
Z., Eds.; Wiley-Interscience: Chichester, 1992, p. 624; (b) In Activation and Functionalization of Alkanes; Hill, C.
L., Ed.; Wiley-Interscience: New York, 1989; (c) Arndsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T.
H. Acc. Chem. Res. 1995, 28, 154.
2. (a) Barton, D. H. R.; Doller, D. Acc. Chem. Res. 1992, 25, 504. (b) Sommer, J.; Bukala, J. Acc. Chem. Res, 1993,
26, 370. (c) Hill, C. L. Synlett. 1995, 127. (d) Fujiwara, Y.; Takaki, K.; Taniguchi Y. Synlett. 1996, 591. (e) Ryu,
I.; Sonoda, N. Angew. Chem., Int. Ed. 1996, 35, 1051. (f) Akhrem, I. Topics Catal. 1998, 6, 27. (g) Paatz, R.;
Weisgerber. G. Chem. Ber. 1967, 100, 984. (h) Kato, S.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. J. Org. Chem. 1998,
63, 222 (and references 2–10 cited therein). (i) Orlinkov, A.; Akhrem, I.; Vitt, S. Mendeleev Commun. 1999, 5, 198.
(j) Akhrem, I.; Orlinkov, A.; Afanas’eva, L.; Petrovskii, P.; Vitt, S. Tetrahedron Lett. 1999, 40, 5897.
3. (a) Akhrem I.; Orlinkov, A.; Vol’pin, M. J. Chem. Soc., Chem. Commun. 1993, 671; (b) Akhrem, I. S.; Orlinkov,
A. V. Russ. Chem. Bull. 1998, 47, 740 [Izv. Acad. Nauk, Ser. khim. 1998, 47, 771. Engl. Transl.].
4. Stull, D. R.; Westrum, E. F.; Sinke, G. R. Chemical Thermodynamics of Organic Compounds; Wiley-Interscience:
New York, 1969.

9907
5. A solution of tetrabromomethane and anhydrous aluminium bromide in molar ratio 1:2 in methylene bromide
(2 ml per 1 g of AlBr3) was cooled to −40°C (or to −20°C), and the reaction flask was filled with gaseous CO.
Then a hydrocarbon was added under CO atmosphere. The mixture was stirred under slightly excessive pressure
i
of CO at −40°C (or at −20°C) for 0.5–2 h. Then an excess of PrOH was carefully added, the reaction mixture
was left to warm up to room temperature and stirred for an additional 30 min. After water work-up, extraction
with ether and drying with MgSO4 the reaction products were analysed by GC and GC-MS. For NMR studies,
1
ether and other light products were distilled from ether extracts. Spectral data: 1, H NMR (l, ppm from TMS):
3
1.10 (s, 3H, CH3), 1.29 (d, 6H, CH3, J=6.4 Hz), 1.10–2.10 (m, 10H, CH2 of cyclo-C6H10), 5.00 (sept., 1H, CH,
J=6.4 Hz); 13C NMR (l, ppm from TMS): 21.71 (2 CH3), 23.19 (2 CH2), 25.71 (1CH2), 26.50 (1CH3), 35.49 (2
CH2,), 42.85 (1C), 66.84 (1CH); 176.74 (1CO); MS, m/z (Irel., %): 184 (M+, 3), 142 (11), 97 (95), 96 (15), 87 (25),
1
3
81 (20), 69 (12), 67 (13). 2, H NMR (l, ppm from TMS): 0.93 (t, 3H, CH3, J=8.0 Hz), 1.22 (d., 6H, CH3,
3J=6.0 Hz), 1.00–2.10 (m, 12H, CH2), 5.00 (sept., 1H, CH, J=6.0 Hz); 13C NMR (l, ppm from TMS): 8.41
3
(1CH3), 21.75 (2 CH3), 23.30 (2 CH2), 26.09 (1CH2), 33.40 (1CH2), 33.82 (2 CH2), 46.93 (1C), 66.66 (1CH),
175.59 (1CO); MS, m/z (Irel., %): 198 (M+, 5), 170 (10), 156 (15), 127 (15), 111 (90), 110 (51), 109 (13), 101 (51),
81 (50), 57 (17), 53 (16).
6. Orlinkov, A. V.; Akhrem, I. S.; Vol’pin, M. E. Russ. Rev. 1991, 60, 920 [Uspekhi Khimii 1991, 60, 1049. Engl.
Transl.].
7. Guschin, P. P.; Lebedev, E. V.; Pivovarova, T. E. Neftekhimiya 1972, 12, 383.
8. Turova-Polyak, M. B.; Sidel’kovskaya, F. P. Zh. Org. Khimii (Russ.) 1941, 11, 817.
9. Petrov, A. A. Khimiya Naftenov, 1971, Nauka, Moscow, p. 191 (table 63).
10. Souma, Y.; Sano, H. J. Org. Chem. 1973, 38, 3633. (b) Souma, Y.; Sano, H. Bull. Soc. Chim. Jpn. 1974, 47, 1717.
(c) Souma, Y.; Sano, H. Bull. Soc. Chim. Jpn. 1976, 49, 3296.
.