Alkylation of alkenes: Ethylaluminum sesquichloride-mediated hydro-alkyl additions with alkyl chloroformates and di-tert-butylpyrocarbonate

Article abstract of DOI:10.1021/ja048904y

A general method for the hydro-alkyl addition to the nonactivated C=C double bond of alkenes using alkyl chloroformates (primary, secondary), 12, and di-tert-butylpyrocarbonate, 52, mediated by ethylaluminum sesquichloride (Et₃Al₂Cl₃) has been developed. Reaction of 12 and 52, respectively, with Et₃Al₂Cl₃ gives an alkyl cation which is added to the alkene; hydride transfer to the adduct carbenium ion or, if applicable, 1,2-H shift followed by hydride transfer from Et₃Al₂Cl₃ to the rearranged adduct carbenium ion gives the saturated addition product. The reaction has been applied to 1-alkenes, 2-methyl-1-alkenes, internal double bonds, and to three cyclic alkenes. Special interest has been focused on alkylations of unsaturated fatty compounds, such as oleic acid (2), which are important renewable feedstocks. 2-Methylalkanes, 3-methylalkanes, 2,4-dimethylalkanes, 2,3-dimethylalkanes, 2,2,4-trimethylalkanes, cyclohexylalkanes, and carboxylic acids and esters with the respective branched alkyl chain have been synthesized with good to moderate yields.

Full text of DOI:10.1021/ja048904y

Published on Web 07/28/2004
Alkylation of Alkenes: Ethylaluminum
Sesquichloride-Mediated Hydro-Alkyl Additions with Alkyl
Chloroformates and Di-tert-butylpyrocarbonate
Ursula Biermann and J u¨ rgen O. Metzger*
Contribution from the Department of Pure and Applied Chemistry, UniVersity of Oldenburg,
D-26111 Oldenburg, Germany
Received February 26, 2004; E-mail: juergen.metzger@uni-oldenburg.de
Abstract: A general method for the hydro-alkyl addition to the nonactivated CdC double bond of alkenes
using alkyl chloroformates (primary, secondary), 12, and di-tert-butylpyrocarbonate, 52, mediated by
ethylaluminum sesquichloride (Et
Et Al Cl gives an alkyl cation which is added to the alkene; hydride transfer to the adduct carbenium ion
or, if applicable, 1,2-H shift followed by hydride transfer from Et Al Cl to the rearranged adduct carbenium
3 2 3
Al Cl ) has been developed. Reaction of 12 and 52, respectively, with
3
2
3
3
2
3
ion gives the saturated addition product. The reaction has been applied to 1-alkenes, 2-methyl-1-alkenes,
internal double bonds, and to three cyclic alkenes. Special interest has been focused on alkylations of
unsaturated fatty compounds, such as oleic acid (2), which are important renewable feedstocks.
2-Methylalkanes, 3-methylalkanes, 2,4-dimethylalkanes, 2,3-dimethylalkanes, 2,2,4-trimethylalkanes, cy-
clohexylalkanes, and carboxylic acids and esters with the respective branched alkyl chain have been
synthesized with good to moderate yields.
Introduction
particular, considered factors which would favor the formation
of mono-alkylation products. It was stated that 1:1 addition
The alkylation of alkenes is of considerable importance.1
However, there are no methods for the direct alkylation of
nonactivated CdC double bonds with alkyl residues, such as
the isopropyl group. Thermal radical additions of alkanes are
applicable to terminal double bonds only, not to internal double
products are formed if the alkyl halide reacts faster with the
alkene than with the alkylation product; otherwise, higher
7
addition products will be obtained. The relative dissociation
rates of the alkyl halide and the alkylation product induced by
the Lewis acid should reflect their relative rates of addition to
2
,3
bonds. Cationic additions are restricted to tertiary alkanes:
for example, the formation of isooctane by the reaction of
isobutene and isobutane in the presence of concentrated acids
7
a
a common alkene. Thus, mono alkylation products with
isopropyl halides were neither obtained in reactions with propene
7
b
and isobutene nor in the corresponding reactions with buta-
4
and superacids. Friedel-Crafts alkylations of alkenes are rarely
11
diene and isoprene. Exclusively, oligomers and polymers were
formed. In contrast, the AlCl3-induced condensation of tert-
butyl chloride with propene afforded a mixture of isomeric
used in preparative organic synthesis to form new CsC bonds
because they tend to give mixtures of products, including
oligomers and polymers of alkenes and mostly not the desired
mono alkylation products. Alkylations of alkenes have been
thoroughly investigated by Olah6 and Mayr,
1
2
heptyl chlorides in 70% yield. The formation of isomers
5
1
3
depends on the applied Lewis acid. Mayr and Striepe found
that the reaction of tert-butyl chloride and propene induced by
ZnCl2‚Et2O gave exclusively the mono-alkylation product
7-10
who, in
(
1) Industrial and Laboratory Alkylations; Albright, L. F., Goldsby, A. R.,
7
b
Eds.; ACS Symposium Series 1977; American Chemical Society: Wash-
ington, DC, 1978.
2-chloro-4,4-dimethylpentane.
It is known that alkyl chloroformates are fragmented in the
(
(
(
2) Metzger, J. O. J. Prakt. Chem. 1990, 332, 767-781.
3) Metzger, J. O.; Bangert, F. Fat Sci. Technol. 1995, 97, 7-9.
4) (a) Pines, H. In The Chemistry of Catalytic Hydrocarbon ConVersions;
Academic Press: New York, 1981; pp 50-58. (b) Nenitzescu, C. D. In
Carbonium Ions; Olah, G. A., von R. Schleyer, P., Eds.; Wiley: New York,
presence of AlCl3, with formation of CO2 and the corresponding
14,15
carbenium ions.
Also, silver(I)-induced dechlorodecarboxyl-
ations were used to generate reactive carbocations from alkyl
1
970; Vol. II, pp 463-520 (at p 504). (c) Olah, G. A.; Farooq O.;
Krishnamurthy, V. V.; Prakash, G. K. S.; Laali, K. J. Am. Chem. Soc. 1985,
07, 7541-7545. (d) Olah, G. A.; Batamack, P.; Deffieux, D.; Torok, B.;
1
(9) (a) Mayr, H.; Schneider, R.; Schade, C.; Bartl, J.; Bederke, R. J. Am. Chem.
Soc. 1990, 112, 4446-4454. (b) Mayr, H.; Schneider, R.; Irrgang, B.;
Schade, C. J. Am. Chem. Soc. 1990, 112, 4454-4459.
Wang, Q.; Molnar, A.; Prakash, G. K. S. Appl. Catal., A 1996, 146, 107-
1
1
17. (e) Olah, G. A.; Marinez, E.; Torok, B.; Prakash, G. K. S. Catal. Lett.
999, 61, 105-110.
(10) (a) Mayr, H.; Patz, M. Angew. Chem. 1994, 106, 990-1010; Angew. Chem.,
Int. Ed. Engl. 1994, 33, 938-957; (b) Mayr, H.; Bug, T.; Gotta, M. F.;
Hering, N.; Irrgang, B.; Janker, B.; Kempf, B.; Loos, R.; Ofial, A. R.;
Remennikov, G.; Schimmel, H. J. Am. Chem. Soc. 2001, 123, 9500-9512.
(11) Petrov, A. A.; Leets, K. V. Zh. Obshch. Khim. 1956, 26, 1113, Chem. Abstr.
1956, 50, 11936d.
(
(
(
5) Kennedy, P.; Mar e´ chal, E. In Carbocationic Polymerization; Wiley-
Interscience: New York, 1982; p 82.
6) Olah, G. A.; Kuhn, S. J.; Barnes, D. G. J. Org. Chem. 1964, 29, 2685-
2
687.
7) (a) Mayr, H. Angew. Chem. 1981, 93, 202-204; Angew. Chem., Int. Ed.
Engl. 1981, 20, 184-186. (b) Mayr, H.; Striepe, W. J. Org. Chem. 1983,
(12) Miller, V. A. J. Am. Chem. Soc. 1947, 69, 1764-1768.
4
8, 1159-1165.
(13) Schmerling, L. J. Am. Chem. Soc. 1953, 75, 6217-6222.
(14) Kevill, D. N. In The Chemistry of Acyl Halides, Chloroformate Esters and
Related Compounds; Patai, S., Ed.; Wiley: London 1972, pp 425-433.
(
8) Mayr, H. Angew. Chem. 1990, 102, 1415-1428; Angew. Chem., Int. Ed.
Engl. 1990, 29, 1371-1384.
10.1021/ja048904y CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 10319-10330
9
10319

A R T I C L E S
Biermann and Metzger
Scheme 1. Friedel-Crafts Alkylation of Arenes by AlCl3-Induced
14 a
Formation of Carbenium Ions from Chloroformates
a
(Ar ) Aryl, R ) Alkyl)
chloroformates. Previously Friedel and Crafts,17 as well as
1
6
1
8
Rennie, showed that benzene is ethylated with ethyl chloro-
formate in the presence of AlCl3 (Scheme 1).
Our special interest lies in the alkylation of long-chain
unsaturated fatty compounds, such as oleic acid (2), since they
19-21
are renewable raw materials of increasing significance
and
alkyl-branched fatty compounds have interesting properties
which make them attractive for use in cosmetic and lubricant
2
2,23
applications.
Most of these characteristics, such as good
spreadability, low viscosity, and good oxidative and hydrolytic
stability, are shown by the commercially available product
“
isostearic acid” that is used in cosmetics and lubricants.
However, this commercial isostearic acid that is formed as a
byproduct in the montmorillonite-induced dimerization process
of oleic acid is not at all a pure compoundsit consists of a
mixture of an immense number of components.24 The synthesis
of well-defined and completely characterized alkyl-branched
fatty compounds by an addition reaction to, e.g., oleic acid,
would be important.
We now report the results of our study, aimed to develop a
general synthetic method for the hydro-alkylation of nonacti-
vated CdC double bonds of alkenes with alkyl chloroformates
mediated by ethylaluminum sesquichloride (Et3Al2Cl3). Dichlo-
romethane has been used as solvent without any nucleophilic
properties. We performed a systematic investigation of the scope
of the reaction with respect to alkenes (Figure 1) and to alkyl
chloroformates (Figure 2) and could establish reaction conditions
that allow the synthesis of the desired alkylation products in
good to moderate yields.25
Figure 1. Alkenes 1-11 used in alkylation reactions.
Results
First, we studied the hydro-alkyl addition to the 1,2-disub-
stituted CdC double bond of alkenes, such as trans-4-octene
(
15) (a) Olah, G. A.; Olah, J. A. In Carbonium Ions; Olah, G. A., von R.
Schleyer, P., Eds.; Wiley: New York, 1970; Vol. II, pp 715-782 (at p
7
65). (b) Kirmse, B. Top Curr. Chem. 1979, 80, 125-311 (at p 172).
(
(
(
(
16) Beak, P. Acc. Chem. Res. 1976, 9, 230-236.
17) Friedel, C.; Crafts, J. M. C. R. Seances Acad. Sci. 1877, 84, 1450-1454.
18) Rennie, E. H. J. J. Chem. Soc. 1882, 41, 33.
19) (a) Biermann, U.; Friedt, W.; Lang, S.; L u¨ hs, W.; Machm u¨ ller, G.; Metzger,
J. O.; R u¨ sch gen. Klaas, M.; Sch a¨ fer, H. J.; Schneider, M. P. Angew. Chem.
2
000, 112, 2292-2310; Angew. Chem., Int. Ed. 2000, 39, 2206-2224. (b)
Biermann, U.; Metzger, J. O. Top. Catal. 2004, 27, 119-130. (c) Eissen,
M.; Metzger, J. O.; Schmidt, E.; Schneidewind, U. Angew. Chem. 2002,
Figure 2. Alkylation agents: alkyl chloroformates 12a-l.
1
14, 402-425; Angew. Chem., Int. Ed. 2002, 41, 414-436.
(20) Syntheses of NoVel Fatty Acid DeriVatiVes; Knothe, G., Derksen, J. T. P.,
(1), oleic acid (2), methyl oleate (3), and methyl ricinoleate (4),
Eds.; American Oil Chemists Society: Champaign, IL, 1999.
(
21) Biermann, U.; F u¨ rmeier, S.; Metzger, J. O. In Oleochemical Manufacture
and Applications; Gunstone, F. D., Hamilton, R. J., Eds.; Sheffield
Academic Press and CRC Press: Boca Raton, FL, 2001, 266-299.
22) Kinsman, D. V. In Fatty Acids in Industry; Johnson, R. W., Fritz, E., Eds.;
Marcel Dekker: New York, 1989; pp 233-276.
and of cyclic alkenes, such as cyclohexene (5) and cyclopentene
(11), using chloroformates of secondary alcohols, such as
isopropyl (12a), cyclohexyl (12b), and 2-pentyl chloroformate
(12c), as alkylating agents (Table 1). All products were unam-
(
(
23) Johnson, R. W., Jr.; Cantrell, R. R. In Kirk Othmer Encyclopedia of
Chemical Technology, 4th ed.; New York: Wiley, 1993; Vol. 5, 189-
1
13
biguously identified and characterized by H NMR, C NMR,
GC/MS, and if applicable, by comparison with literature data.
Dropwise addition of ethylaluminum sesquichloride (Et3Al2-
Cl3) to a mixture of alkene 1 and isopropyl chloroformate (12a)
1
92.
(
24) Technical Data Sheet, Emersol 874 Isostearic Acid, Henkel Coorporation:
Gulph Mills, PA, 1999.
(25) For a preliminary account of our results, see: Biermann, U.; Metzger, J.
O. Angew. Chem., Int. Ed. 1999, 38, 3675-3677.
10320 J. AM. CHEM. SOC.
9
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Alkylation of Alkenes with Ethylaluminum Sesquichloride
A R T I C L E S
Table 1. Ethylaluminum Sesquichloride (Et3Al2Cl3)-Induced Alkylations of Alkenes 1-11 with Secondary Alkyl Chloroformates: Isopropyl
(12a), Cyclohexyl (12b), and 2-Pentyl Chloroformate (12c)
a
Isolated yields were obtained by Kugelrohr distillationsexcept for products 14/15, 20/21, 27, 29, and 30/31 which were obtained by column chromatography
b
(
(
see Experimental Section). The regioisomeric products 18 and 19 were obtained as mixtures of diasteromers, respectively, in ratios of 7:1 (18) and 5:3
19). The reaction was carried out with equimolar amounts of Et3Al2Cl3 and triethylsilane.
c
J. AM. CHEM. SOC.
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A R T I C L E S
Biermann and Metzger
Scheme 2. Mechanism of the Hydro-Alkylation of Internal Alkenes
with Isopropyl Chloroformate (12a) and Ethylaluminum
Sesquichloride
The hydro-alkyl addition to cyclic alkenes, such as cyclo-
hexene (5) and cyclopentene (11), with isopropyl chloroformate
12a) under the standard reaction conditions described for alkene
(
1
occurred with only moderate yields, e.g., 40%, of isopropyl-
cyclohexane (22). Product mixtures, which consisted mainly of
oligomers, were formed. However, the formation of the mono-
alkylation products could be favored by addition of a more
1
0
effective hydride donor, such as triethylsilane. Thus, the
isopropylation of 5, which was carried out by dropwise addition
of an equimolar mixture of triethylsilane and Et3AlCl3 to the
mixture of 5 and 12a, afforded isopropylcyclohexane (22) in a
2
5
remarkable yield of 82% (Table 1, entry 6). The oligomer-
ization was extensively suppressed using these modified standard
reaction conditions. Isopropylcyclopentane (23) was synthezised
in 69% yield using comparable reaction conditions (Table 1,
entry 7). Remarkably, cis- and trans-1,2-dimethylcyclohexane
were detected as minor products (together, 3.5%) by GC/MS.
The reaction was also applied to the trialkyl-substituted CdC
double bond of 1-methyl cyclohexene (6). The alkylation of 6
with 12a was already complete after a reaction time of 1 h and
gave o-menthane, 24, in a yield of 49% as a diastereomeric
mixture in a ratio of [trans-24]:[cis-24] ) 1.5:1 (Table 1, entry
in dichloromethane in a ratio of 1:1:1 gave, after 1 h of reaction
time at -15 °C and stirring for an additional 1 h at room
temperature, the hydro-alkyl-addition product 4-isopropyloctane
(13) in 67% yield (Table 1, entry 1). These are the standard
reaction conditions that are used in the following experiments.
It is important to use 1 equiv of Et3Al2Cl3; 0.5 equiv is necessary
for the chloro abstraction from the chloroformate, and 0.5 equiv
is consumed in the hydride transfer to the adduct carbenium
ion (see Scheme 2). Rearranged addition products and isomeric
ethyl-isopropyloctanes were formed in small amounts, about
8
). The isopropylation of 2-methyl-1-undecene (8), using
standard reaction conditions, yielded only 10% of 2,4-dimeth-
yltridecane (26). An additional product formed, in 45% yield,
was 10,10,13-trimethyleicosane, the hydrodimer of 8, as was
shown by GC/MS. Addition of equimolar amounts of triethyl-
silane afforded a 47% yield of 26 but did not suppress the
formation of the dimer completely (Table 1, entry 10). Most
interesting was the hydro-isopropyl addition to 1-alkenes, giving
selective access to 2-methylalkanes. The reaction of 1-octene
10% of the overall yield. Most reactions described in this paper
showed comparable minor products (<10%) that will be
outlined, furthermore, only in special examples. Chloro isopro-
pyloctanes and isopropyloctenes were not detected, or were
detected only in trace amounts, by GC/MS. The range of
temperature that can be used to perform the reaction successfully
is very small, thus preventing the investigation of the temper-
ature dependence.
(7), 10-undecenoic acid (9), and methyl 10-undecenoate (10)
was studied. Under standard reaction conditions, the desired
addition products were obtained in low yields only (e.g., reacting
chloroformate 12a with 10-undecenoic acid (9) produced hydro-
alkyl-addition product 27 in 10% yield, as determined by GC,
because of dimerization and oligomerization of alkene 9). By
applying modified standard reaction conditions with addition
of equimolar amounts of triethylsilane (alkene:12a:Et3Al2Cl3:
Et3SiH ) 1:1:1:1), oligomerization of the alkenes was consider-
ably suppressed so that the mono-alkylation products 25, 27,
and 28 were isolated in yields of 55%, 60%, and 72%,
respectively (Table 1, entries 9, 11, and 12).
Alkylations of unsaturated fatty compounds 2 and 3, contain-
ing two different alkyl substituents at the cis-configured double
bond, afforded the regioisomeric mixtures of 9- and 10-
isopropyloctadecanoic acid (14 and 15) and the respective
methyl esters (16 and 17) in 73% and 71% yield, respectively
(Table 1, entries 2 and 3). The regioisomers that could not be
separated by chromatographic and other usual separation
methods were obtained in a ratio of approximately 1:1. A
respective mixture of the regioisomers 9- and 10-cyclohexyl-
octadecanoic acid (20 and 21) was formed on reaction of alkene
2
with cyclohexyl chloroformate (12b) (Table 1, entry 5). It
The hydro-cyclohexyl addition to 1-alkenes opens an easy
way to 1-cyclohexylalkanes. Reaction of 10-undecenoic acid
seems to be remarkable that the yield is not diminished reacting
substrates with carboxy and ester functionalities. In these
reactions, it is important to apply 1.5 equiv of Et3Al2Cl3 because
(9) with cyclohexyl chloroformate (12b) in the presence of
equimolar amounts of Et3Al2Cl3 and triethylsilane afforded 11-
cyclohexylundecanoic acid (29) in an isolated yield of 58%
(Table 1, entry 13).
0
.5 equiv is used by the carboxy group and the ester group,
respectively. Also, an additional hydroxy group in the â-position
relative to the CdC double bond is tolerated. The isopropylation
of methyl ricinoleate (4) gave the alkylation products in 60%
yield as a mixture of the two regioisomers 18 and 19 in a ratio
of approximately 1:1. Both were formed as a pair of diastereo-
mers; 18 in a ratio of 7:1 and 19 in a ratio of 5:3. The
diastereomers were distinguishable by GC analysis and by the
2
-Pentyl chloroformate (12c) as a further secondary alkyl
chloroformate was studied additionally because of a possible
rearrangement of the intermediate 2-pentyl cation. As expected,
in contrast to the respective reactions with chloroformates 12a
and 12b, alkylation products obtained with 12c were formed
as mixtures of isomers. The alkylation of 10-undecenoic acid
(9) yielded 72% of a mixture of 12-methylpentadecanoic acid
(30) and 12-ethyltetradecanoic acid (31) in a ratio of 1.2:1 (Table
1, entry 14). 3-Pentyl chloroformate (12l) yielded the same ratio
of the respective isomers in the corresponding reaction with
cyclohexene (5) (Table 2, entry 6).
13
C NMR spectrum, but they could not be assigned unambigu-
ouly to the respective compounds. In this example, 2 equiv of
Et3Al2Cl3 had to be applied because the reaction of the additional
hydroxyl group with Et3Al2Cl3 consumes 0.5 equiv (Table 1,
entry 4).
10322 J. AM. CHEM. SOC.
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Alkylation of Alkenes with Ethylaluminum Sesquichloride
A R T I C L E S
Table 2. Ethylaluminum Sesquichloride (Et3Al2Cl3)-Induced Alkylations of Alkenes 2, 5, and 9 with Linear Primary Alkyl Chloroformates:
1-Propyl (12d), 1-Butyl (12e), 1-Pentyl (12f), and 1-Hexyl Chloroformate (12g)
a
Isolated yields were obtained by column chromatographysexcept for product 35, which was obtained by Kugelrohr distillation (see Experimental
Section). The reaction was carried out with equimolar amounts of Et3Al2Cl3 and triethylsilane. c Using 3-pentyl chloroformate (12l), the ratio of [36]:[37]
b
)
1.2:1 was obtained.
Having investigated the very general addition reactions of
secondary alkyl chloroformates, we draw our attention to linear
primary alkyl chloroformates. Reactions of ethyl chloroformate
equimolar amounts of triethylsilane showed the addition of the
2-butyl cation, yielding 72% of 12-methyltetradecanoic acid
(34). Cyclohexene (5) yielded only 30% of sec-butylcyclohexane
(35). In addition, cyclohexylcyclohexane (36%, GC) was
formed, the formation of which could not be suppressed by the
addition of Et3SiH.
Higher linear alkyl chloroformates are expected to give
isomers by addition of the possible secondary alkyl groups
which can be formed by Wagner-Meerwein rearrangements.
Thus, alkylation of alkene 5 with chloroformate 12f in the
presence of triethylsilane yielded mixtures of 2- and 3-cyclo-
hexylpentane in a ratio of [36]:[37] ) 1.3:1. A product ratio of
1.2:1 was obtained using 3-pentyl chloroformate (12l) (Table
2, entry 6). A mixture of 12-methylhexadecanoic acid (40) and
of 12-ethylpentadecanoic acid (41) in a ratio of [40]:[41] ) 1.1:1
was obtained from the alkylation of alkene 9 with chloroformate
12g in the presence of triethylsilane (Table 2, entry 8).
Approximately the same ratio of products 38 and 39 was formed
with alkene 5 (Table 2, entry 7).
(
12k) with 1-alkenes under standard reaction conditions, as well
as with added triethylsilane, gave oligomerization of the alkene,
e.g., the reaction of 9 and chloroformate 12k resulted in the
formation of a mixture of C22 dicarboxylic acids in 70% yield,
as was shown by GC/MS. However, reacting 1-propyl chloro-
formate (12d) under standard reaction conditions with oleic acid
(
1
2) gave a mixture of 9- and 10-isopropyloctadecanoic acid (14,
5) in a yield of 71% (Table 2, entry 1). Thus, the same product
mixture and almost the same yield were obtained as with
isopropyl chloroformate (12a) (Table 1, entry 2). Analogously,
reaction of chloroformate 12d and 10-undecenoic acid (9) with
added triethylsilane gave 12-methyltridecanoic acid (27) in 56%
yield (Table 2, entry 2).
Using 1-butyl chloroformate (12e) in the reaction, the addition
of the sec-butyl group could be expected. Indeed, reaction of
oleic acid (2) under standard reaction conditions with chloro-
formate 12e afforded the regioisomeric mixture of 9- and 10-
sec-butyloctadecanoic acid (32, 33) in 74% yield. Analogously,
reaction of alkene 9 with chloroformate 12e in the presence of
It seems worth mentioning that, in all examples of reactions
with primary alkyl chloroformates investigated, no hydro-1-
alkyl-addition products could be detected. Primary alkyl chlo-
J. AM. CHEM. SOC.
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A R T I C L E S
Biermann and Metzger
Table 3. Ethylaluminum Sesquichloride-Induced Alkylations of Alkenes 2, 5, 9, and 11 with Branched Primary Alkyl Chloroformates:
Isobutyl (12h) and Neopentyl Chloroformate (12I)
a
Isolated yields were obtained by column chromatography (32/33/42/43, 34/44, and 46/47) or by Kugelrohr distillation (35/45/54, 48/49, and 50/51) (see
Experimental Section). The reaction was carried out with equimolar amounts of Et3Al2Cl3 and triethylsilane. c 1:1 Mixture of diastereomers.
b
Table 4. Ethylaluminum Sesquichloride-Induced Alkylations of
Alkenes 2, 5, 8, 9, and 11 with Di-tert-butylpyrocarbonate (52)
roformates that are branched at C-2 lead to the formation of
interesting, rearranged addition products. We treated, therefore,
oleic acid (2) with isobutyl chloroformate (12h) in the presence
of Et3Al2Cl3 and obtained a mixture of hydro-alkyl addition
products 32, 33 and 42, 43 in 74% overall yield (Table 3, entry
1
). Regioisomers 32 and 33 were also formed by reaction of 2
with 1-butyl chloroformate (12e) (Table 2, entry 3). Regioiso-
mers 42 and 43 are the products of hydro-tert-butyl addition to
the double bond and were also formed by reacting alkene 2
with di-tert-butylpyrocarbonate (52) (Table 4, entry 1). The ratio
of ([32]+[33]):([42]+[43]) was approximately 2:1. Reaction of
the same chloroformate, 12h, with 1-alkene 9 showed a different
outcome of products. Two isomeric addition products 34 and
4
4, in a ratio of 1:2.2, were obtained. Whereas 34 was also
obtained by addition of 1-butyl chloroformate (12e), no tert-
butyl addition product was observed. Instead 11,12-dimethyl-
tridecanoic acid (44) was formed (Table 3, entry 2), which was
also obtained by reaction of 9 with di-tert-butylpyrocarbonate
(
(
52) (Table 4, entry 2). The respective reaction of cyclohexene
5) gave 2-butylcyclohexane (35), 1-isopropyl-1-methylcyclo-
a
hexane (45), and tert-butylcyclohexane (54) in a ratio of 12.5:
.5:1. Product 35 was also formed in the reaction with
chloroformate 12e (Table 2, entry 5), and products 45 and 54
Isolated yields were obtained by column chromatography (42/43 and
4
4) or by Kugelrohr distillation (53, 45/54, and 55) (see Experimental
Section). The reaction was carried out with equimolar amounts of Et3Al2Cl3
and triethylsilane.
2
b
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Alkylation of Alkenes with Ethylaluminum Sesquichloride
A R T I C L E S
were obtained by reaction with di-tert-butylpyrocarbonate (52).
2, entry 4). 2,4-Dimethylalkanes may be obtained by reaction
of 2-methyl-1-alkenes with isopropyl chloroformate (Table 1,
entry 10), and 2,3-dimethylalkanes may be obtained by reaction
of 1-alkenes with di-tert-butylpyrocarbonate (52) (Table 4, entry
2). Reacting 2-methyl-1-alkenes with 52 can provide 2,2,4-
trimethylalkanes (Table 4, entry 3). Cyclohexylalkanes can
generally be synthesized by reacting cyclohexyl chloroformate
(12b) with alkenes (Table 1, entries 6 and 13). 11-Cyclohexyl-
undecanoic acid (29) is known to be the main lipid of
(Table 3, entry 3; see also Table 4, entry 4).
It is remarkable that the alkylations of 9 and 5 with 12h (Table
3
, entries 2 and 3) showed only very small amounts of
oligomerization products (>8%), although they were carried out
under standard reaction conditions without addition of trieth-
ylsilane. In all examples described here, no trace of a hydro-
isobutyl-addition product could be observed.
Next, neopentyl chloroformate (12i) was reacted with alkene
27
9
. 11,12-Dimethyltetradecanoic acid (46) and 11-ethyl-12-
thermophilic archaebacteria. The synthesis of the methyl ester
methyltridecanoic acid (47) were formed in a ratio of 2.2:1 and
isolated in an overall yield of 70% (Table 3, entry 4). 46 was
formed as a diastereomeric mixture in a ratio of about 1:1, as
was shown by 13C NMR. The respective reaction with cyclo-
hexene (5) afforded 1-ethyl-1-isopropylcyclohexane (48) and
of 29 has been performed by thermal radical addition of
cyclohexane to the methyl ester of 9 (yield ) 30%), a method
3
which is restricted to 1-alkenes for the synthesis of 1-cyclo-
2
hexylalkanes.
The main phenomena emerging from the results described
in the preceding section, which should be posed for discussion,
certainly are the differences in the substitution patterns of the
addition products which may be influenced by the respective
alkyl group of the chloroformate 12, as well as by the alkene
being reacted. Furthermore, an important phenomenon to be
explained is the fact that the hydro-alkyl addition could be
performed in many cases, e.g., with internal alkenes, under
standard reaction conditions with the reagent ethylaluminum
sesquichloride only, whereas in other examples, e.g., with
1-alkenes, the standard reaction conditions had to be modified
by the addition of triethylsilane as an additional hydride donor
to suppress the formation of oligomers. In contrast, when
reacting alkenes 6 and 8, the formation of dimers could only
partially be suppressed by triethylsilane. The reaction mechanism
should be able to explain these phenomena.
1
-(2-butyl)-1-methylcyclohexane (49) in a ratio of 1.3:1 and
an overall yield of 84% (Table 3, entry 5). Most interesting
results were obtained reacting cyclopentene (11) with chloro-
formate 12i. A mixture of 1-ethyl-1,2-dimethylcyclohexane (50)
and 1-ethyl-2,2-dimethylcyclohexane (51) in a ratio of 2.8:1 and
an overall yield of 65% were obtained. The two diastereomers
of 50 were formed unselectively in a ratio of about 1:1, as was
shown by 13C NMR.
Finally, we were interested in the possibility of the addition
of the tert-butyl group to nonactivated double bonds of alkenes.
Because of its thermal instability, tert-butyl chloroformate could
not be used, corresponding to 12a-l, to study these reactions,
so di-tert-butylpyrocarbonate (52) was applied to perform the
reaction with alkenes 2, 5, and 9 (Table 4). To our complete
satisfaction, pyrocarbonate 52 behaved as the chloroformates,
1
2. The products obtained were already described for reactions
The basic reaction mechanism can be rationalized easily if
alkylations were carried out with simple secondary alkyl
chloroformates, such as isopropyl chloroformate (12a) (Scheme
2). In the presence of Et3Al2Cl3, chloroformate 12a decomposes
by formation of CO2 and the isopropyl cation, which adds to
the CdC double bond of an internal alkene to give a secondary
adduct carbenium ion I. One could have thought that hydride
transfer to adduct carbenium ion I gives the hydro-alkyl-addition
product. However, a 1,2-H shift affording the more stable
tertiary carbenium ion II, possibly being in equilibrium with
ion III, seems to be faster, as can be seen in the addition
reactions of tert-butyl cation (see e.g., Scheme 7). Subsequent
transfer of a hydride ion from an ethylaluminum species to the
tertiary carbenium ions II and/or III and elimination of ethene
lead to the hydro-alkyl addition product. It is known that
ethylaluminum compounds can transfer hydride ions as well as
with isobutyl chloroformate 12h. Reaction of alkene 8 with
pyrocarbonate 52 gave 2,2,4-trimethyltridecane (53), which
could be isolated in 43% yield only (Table 4, entry 3). The
dimerization of 8, which resulted in the formation of about 18%
of 10,10,12-trimethylicosane (GC), could not also be fully
suppressed in the presence of Et3SiH.
Finally, cyclopentene (11) was reacted with 52 (11:52:Et3-
Al2Cl3 ) 2:1:2). To our surprise, we isolated 1,1,2-trimethyl-
cyclohexane (55) in 60% yield (Table 4, entry 5).
Discussion
The newly developed protocol of hydro-alkylation of alkenes
is most important from a preparative point of view. Nonactivated
CdC double bonds of alkenes have been hydro-alkylated using
a very great variety of primary and secondary alkyl chlorofor-
mates, 12, and di-tert-butylpyrocarbonate (52). Various func-
tional groups in the substrate are tolerated. Thus, oleic acid (2),
a renewable feedstock, was hydro-isopropylated to give a 1:1
mixture of 9- and 10-isopropylstearic acid (14, 15) (Table 1,
entry 2)
28
ethyl groups; notably, in this case, the hydride ion is transferred
significantly more rapidly than the ethyl group, as is demon-
strated by the small amount of ethylated products in most
reactions. In addition, as shown in Scheme 3, chloride might
be transferred as well to the carbenium ion to give alkyl-chloro-
7
b
The protocol allows for the highly efficient synthesis of
addition products, and a proton could be eliminated to give
29
2
-methylalkanes (isoalkanes) by reaction of 1-alkenes with
isopropyl and 1-propyl chloroformate (Table 1, entries 9, 11,
2; Table 2, entry 2). ω-Unsaturated fatty acids give, most
alkyl-dehydrogenation products. The possible products of these
two competitive reactions could not be observed and were
formedsif at allsin very small amounts. Finally, the rearranged
adduct carbenium ion could be trapped by the alkene to give
1
easily, (ω-1)-methyl-branched isofatty acids, an important class
of natural compounds. Isofatty acids have been synthesized in
a multistep procedure by Fordyce and Johanson.26 3-Methyla-
lkanes are formed by reaction with 1-butyl chloroformate (Table
(
(
(
27) (a) Handa, S.; Floss. H. G. Chem. Commun. 1997, 153-154. (b) Floss, H.
G. Nat. Prod. Rep. 1997, 14, 433-452.
28) Snider, B. B.; Rodini, D. J.; Karras, M.; Kirk, T. C.; Deutsch, E. A.;
Cordova, R.; Price, R. T. Tetrahedron 1981, 37, 3927-3934.
29) Snider, B. B.; Rodini, D. J.; Kirk, T. C.; Cordova, R. J. Am. Soc. 1982,
104, 555-563.
(26) Fordyce, C. R.; Johnson, J. R. J. Am. Chem. Soc. 1933, 55, 3368-3372.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 33, 2004 10325

A R T I C L E S
Biermann and Metzger
Scheme 3. Possible Competitive Reactions of the Hydro-Alkyl
Addition Shown for the Rearranged Adduct Carbenium Ion II. Ana-
logous Reactions Are Possible with Carbenium Ion III (Scheme 2)
Scheme 4. Mechanism of the Reaction of 2-Methyl-1-undecene
(8) with the Isopropyl Cation Generated from Isopropyl
Chlorformate (12a) in the Presence of Et3Al2Cl3 (see Scheme 2)
Giving Alkylation Product 26 and Hydrodimer
10,10,13-Trimethyleicosane
Scheme 5. Reaction of Pentyl Chloroformates 12f and 12l in the
Presence of Et3Al2Cl3 with Cyclohexene (5) and of 12c with
1
0-Undecenoic Acid (9) Giving the Hydro-Alkylation Products 36,
37 and 30, 31, Respectively
oligomers. This latter competitive reaction seems to be unim-
portant in reactions of internal alkenes because the most stable
intermediate tertiary carbenium ion is sterically crowded and
should be very unreactive in an addition to the internal alkene.
In contrast, during reaction of 1-alkenes, the formed tertiary
carbenium ion is less crowded, and addition to the 1-alkene
will be as fast as or even faster than hydride transfer from the
ethylaluminum species. Fortunately, reaction conditions could
be found (adding Et3SiH) such that hydride transfer to the adduct
carbenium ion is the fastest trapping reaction which enables
the hydro-alkyl-addition products to be obtained in 47-82%
isolated yield (Table 1).
able to perform Wagner-Meerwein rearrangements,30 being
faster than the addition and the hydride transfer reaction. Thus,
This basic reaction mechanism enables us to understand the
results given in Table 1, entries 1-13. As can be expected, the
primarily formed carbenium ion (isopropyl, cyclohexyl) is added
without regioselectivity to oleic acid (2) and the respective
methyl ester 3 (entries 2, 3, and 5). Unfortunately, the addition
to methyl ricinoleate (4) occurs as well without regioselectivity
2
- (12c) and 3-pentyl chloroformate (12l) gave the same ratio
of 2- and 3-addition products of 1.3:1, giving evidence that
3
-pentyl cation is more stable than 2-pentyl cation (Scheme 5).
Reactions of primary alkyl chloroformates gave exclusively
rearranged products with respect to the primary alkyl group
Tables 2 and 3). No primary addition products were observed
(
(
entry 4). Expectedly, high regioselectivity is observed in
reactions of 1-alkenes (entries 9-13) and 1-methylcyclohexene
6) (entry 8). The lowest yields were obtained by reacting
-methyl-1-undecene (8) because hydrodimers of 8 were formed
in contrast to deaminations of 1-aminoalkanes which yielded
rearranged and primary reaction products with water.30 1-Propyl
chloroformate (12d) gave the same addition products and
comparable yields as isopropyl chloroformate (12a). Obviously,
during the Et3Al2Cl3-mediated decomposition of 12d, rearrange-
ment of 1-propyl to isopropyl occurs, possibly by concerted
(
2
in a competitive reaction which could not be fully suppressed
by the addition of Et3SiH. That is remarkable because, in the
primary addition reaction, a stable tertiary cation is formed and
direct hydride transfer to this adduct ion gives product 26
1
,2-H shift and CO2 elimination. The following reaction steps
to give the final product occur as outlined in the basic reaction
scheme (Scheme 2). The same applies to the reactions of
chloroformates 12e-g (Table 2, entries 3-8). The Et3Al2Cl3-
mediated decomposition of neopentyl chloroformate (12i) gives
the tert-pentyl cation (Scheme 6), and the Et3Al2Cl3-mediated
decomposition of isobutyl chloroformate (12h) by two competi-
tive 1,2-shifts of H and CH3 gives tert-butyl and 2-butyl cation,30
respectively, which are added to the respective alkene.
(Scheme 4). However, a stable tertiary cation is formed by
â-hydrogen transfer from the isopropyl cation as well, and
addition to alkene 8 followed by hydride transfer gives, finally,
the hydrodimer. The same considerations apply to reactions of
1-methylcyclohexene (6). The minor yields of additions of butyl,
pentyl, and hexyl cations may be explained by competitive
â-hydrogen transfer from the secondary cations to cyclohexene
(5) to give an internal alkene and a cyclohexyl cation that adds
It can be assumed from the experimental results that the
carbenium ions are fully equilibrated prior the addition to the
alkene. Thus, reacting 2-pentyl chloroformate (12c) with alkene
to cyclohexene, affording finally cylohexylcyclohexane (Table
2, entries 5-7).
It should be pointed out that the carbocations that are
9
(Table 1, entry 14) and 1-pentyl chloroformate (12f), as well
formulated for convenience as free carbocations in schemes 2-7
may exist as ion pairs stabilized by their anionic counterparts
because dichloromethane is neither an ionizing nor a nucleo-
philic solvent. However, the carbocationic species formed are
as 3-pentyl chloroformate (12l) with cyclohexene(5) (Table 2,
(30) Keating, J. T.; Skell, P. S. In Carbonium Ions; Olah, G. A., Schleyer, P. v.
R., Eds.; Wiley: New York, 1970, Vol. II, pp 573-653.
10326 J. AM. CHEM. SOC.
9
VOL. 126, NO. 33, 2004

Alkylation of Alkenes with Ethylaluminum Sesquichloride
A R T I C L E S
Scheme 6. Mechanism of the Reaction of Neopentyl Chloro-
formate (12i) with Ethylaluminum Sesquichloride and 10-Unde-
cenoic Acid (9) Giving Hydro-Alkylation Products 46 and 47
Scheme 7. Mechanism of Reactions of Di-tert-butylpyrocarbonate
(52) in the Presence of Et3Al2Cl3 with Cyclohexene (5) and
Cyclopentene (11) To Give Alkylation Products 45/54 and 55,
Respectively
entry 6), gave the same ratio of 2- and 3-pentyl addition products
(Scheme 5). The same applies to 1-hexyl chloroformate, 12g,
which was added to alkenes 5 and 9 to give the addition products
in a ratio of 1:1 and 1.1:1, respectively (Table 2, entries 7-8).
In comparison, deamination of 2-aminopentane in water gave
2
- and 3-pentanol in a ratio of 3:1.31
Remarkably, a hydro-tert-butyl addition product was only
Addition reactions of tert-alkyl cations to cyclopentene (11)
are most remarkable. Reaction with di-tert-butylpyrocarbonate
(52) gave 1,1,2-trimethylcyclohexane (55) (Table 4, entry 5).
No cyclopentane derivative could be detected. A rationalization
of the formation of 55 is given in Scheme 7. Addition of the
tert-butyl cation to 11 yields a secondary cyclopentyl cation. A
observed by reacting alkenes with a 1,1-dialkyl-substituted
double bond, such as in 8, and with an internal double bond,
such as in 2 and 5, whereas 1-alkene 9 gives the rearranged
product 44 (Table 3, entries 1-3; Table 4, entries 1-4). That
can be straightforwardly rationalized. By addition of tert-butyl
cation to alkene 8, a stable tertiary adduct carbenium ion is
formed, which is reacted with hydride to give product 53. In
contrast, by addition to 1-alkene 9, a secondary adduct carben-
ium ion is obtained which can be stabilized by a 1,2-H shift
and a following 1,2-CH3 shift to give a tertiary carbenium ion.
The following hydride transfer gives, highly selectively and
preparatively very interestingly, a 2,3-dimethyl alkyl compound.
Reacting alkenes containing an internal double bond, tert-
butylated and rearranged products were observed. In the addition
step, a secondary carbenium adduct ion is formed followed by
1,2-H shift followed by a concerted 1,2-CH shift and a ring
3
enlargement gives the most stable endocyclic tert-cyclohexyl
cation and, finally, by hydride transfer, product 55. Ring
enlargement of 1-ethylcyclopentyl to 1-methylcyclohexyl cat-
33
ion and of 2-(2-cyclopentyl)propyl cation to 1,2-dimethylcy-
34
clohexyl cation is well known and studied by quantum
35
mechanical calculations. The respective addition of tert-pentyl
cation by reaction with neopentyl chloroformate (12i) analog-
ously gave the isomeric cyclohexane derivatives 50 and 51
because of a competitive 1,2-shift of methyl and ethyl in the
adduct cation (Table 3, entry 6). Interestingly, reaction of
isopropyl chloroformate (12a) with 11 yielded, as already
discussed, isopropylcyclopentane as the major product (Table
1
,2-H shift to give a tertiary carbenium ion. Now, the product
outcome seems to be controlled thermodynamically. In the case
of alkene 2, the tert-butylated products 42 and 43 are formed
preferably. In contrast, in the case of cyclohexene (5), the
1
, entry 7). As minor products, cis- and trans-dimethylcyclo-
3
2
exocyclic rearranged cation seems to be more stable, and a
hexane could be detected, formed clearly by ring enlargement
as described above. These results show that the most stable
product, carbenium ionic species, are formed, reacting finally
with the hydride donor.
ratio of [45]:[54] ) 5:1 was observed (Scheme 7).
Addition of the tert-pentyl cation to alkene 9 occurs as
outlined above for the tert-butyl cation addition. The difference
is that methyl and ethyl can undergo 1,2-shifts competitively,
giving two isomers (Scheme 6). The ratio of isomers 46 and
7 was found to be 2.2:1. Addition to cyclohexene (5) yielded
analogously the addition products 48 and 49 (Table 3, entries
, 5).
A few examples were studied giving diastereomeric products.
Products 46 and 50 were formed unselectively; whereas the
formation of products 18/19 and 24 showed low stereoselec-
tivity, giving evidence that the reaction scheme may possibly
be useful in stereoselective synthesis.
4
4
(
31) Fry, J. L.; Karabatsos, J. J. In Carbonium Ions; Olah, G. A., Schleyer, P.
v. R., Eds.; Wiley: New York, 1970, Vol. II, pp 521-571.
(33) Lenoir, D.; Siehl, H.-U. In Houben-Weyl; Georg Thieme-Verlag: Stuttgart,
1990, Vol. E19c, p 264.
(34) Vrcek, V.; Siehl, H.-U.; Kronja, O. J. Phys. Org. Chem. 2000, 13, 616-6.
(32) Siehl, H.-U.; Vrcek, V; Kronja, O. J. Chem. Soc., Perkin Trans. 2 2002,
1
06-113.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 33, 2004 10327

A R T I C L E S
Biermann and Metzger
Conclusions
triethylsilane (0.58 g, 5 mmol) and Et
3
Al
2
Cl
3
(1.24 g, 5 mmol) was
then added dropwise over 1h at -15 °C, and the mixture was stirred
for an additional 1 h at room temperature. Diethyl ether (100 mL),
H O (40 mL), and 10% HCl, to dissolve precipitated aluminum salts,
2
were then added. The organic phase was separated and washed with
Our investigation of the ethylaluminum sesquichloride-
mediated hydro-alkylation of a very broad variety of alkenes
with alkyl chloroformates exhibiting different structural features
clearly established the scope of this very general cationic hydro-
alkyl addition as a powerful synthetic tool. Some important
classes of alkyl branched alkanes, e.g., 2-methylalkanes, 3-me-
thylalkanes, 2,4-dimethylalkanes, 2,3-dimethylalkanes, 2,2,4-
trimethylalkanes, and cyclohexylalkanes, can be generally
synthesized with high to moderate yields. Important functional
groups, e.g., carboxy, ester, and hydroxy, are compatible with
the reaction conditions, enabling the selective synthesis of
carboxylic acids, esters, and alcohols with a branched alkyl chain
as given above for the respective alkanes.
H O (3 × 30 mL). The combined extracts were dried over Na SO ,
2
2
4
the solvent was removed in vacuo, and the residues of experiments 8,
10 and 16 were dissolved in pentane and filtered through silica gel 60.
After the pentane was evaporated, purification was achieved by
Kugelrohr distillation. The residues of experiments 11, 12, 13, 15 and
1
7 were purified by column chromatography using petroleum ether/
EtOAc (7:3). Fractions containing the alkylation product were collected,
the solvent was evaporated, and the residue dried at 20 °C/0.01 mbar.
3
. 4-Isopropyloctane (13). The reaction of trans-4-octene (1) (0.56
g, 5 mmol) and isopropyl chloroformate (12a) (0.7 g, 5 mmol) was
carried out as described (procedure 1) and gave, after purification of
the crude product by Kugelrohr distillation, 0.52 g (67%) of 13 as a
Experimental Section
20
1
colorless oil; nD ) 1.4239; H NMR (300.1 MHz) δ ) 0.88 (d, J )
1
. General Methods. All reactions were performed under nitrogen.
6.9 Hz, 6H, CH ), 0.94 (m, 6H, CH ), 1.09 (m, 2H, CH ), 1.32 (m,
3
3
2
13
Solvents were dried and distilled according to standard procedures.
Oleic acid and methyl oleate (new sunflower, 82.8% oleic acid, 3.6%
stearic acid, 3.5% palmitic acid, 8.4% linoleic acid) and methyl
ricinoleate (80-85% purity) were obtained from Cognis. The amounts
of the starting olefins used in the reactions were calculated based on
8H, CH ), 1.74 (m, 1H, 4-H); C NMR (75.5 MHz) δ ) 14.56 and
2
3 2
14.94 (C1 and C8), 19.52 and 19.56 (CH(CH ) ), 21.25 (C7), 23.35,
29.31 (C9), 30.45, 30.63, 33.32, 43.84 (C4); GC/MS (EI), m/z (%)
156(3), 112(66), 71(71), 57(100).
4. Mixture of 9-Isopropyloctadecanoic Acid (14) and 10-Isopro-
pyloctadecanoic acid (15). The reaction of oleic acid (2) (1.41 g, 4.2
mmol) and isopropyl chloroformate (12a) or 1-propyl chlorformate
(12d) (0.7 g, 5 mmol), respectively, was carried out as described
(procedure 1) and gave, after purification of the crude product by
column chromatography, 0.99 g (73%) and 0.97 g (71%), respectively,
1
00% purity. 10-Undecenoic acid and methyl 10-undecenoate were
obtained from Atochem, and Et Al Cl was obtained from Crompton
3
2
3
GmbH. 1-Propyl, 1-hexyl, isobutyl, and neopentyl chloroformate, as
well as 1-octene, trans-4-octene, cyclohexene, cyclopentene, and
2
-methyl-1-undecene, were purchased from Aldrich and used as
19
received. Isopropyl, cyclohexyl, and 1-butyl chloroformate were
obtained from BASF, and 1-, 2-, and 3-pentyl chloroformate were
of a mixture of 14 and 15 (≈1:1) as a corlorless oil; n ) 1.4588.
D
5. Mixture of Methyl 9-Isopropyloctadecanoate (16) and Methyl
36
synthezised as described. For column chromatography Merck 60 silica
gel, 70-230 mesh, was used. Analytical GC was performed on a Carlo
Erba GC series 4160 with an FID detector and fused silica capillary
1
0-Isopropyloctadecanoate (17). The reaction of methyl oleate (3)
(1.48 g, 4.2 mmol) and isopropyl chloroformate (12a) (0.7 g, 5 mmol)
was carried out as described (procedure 1) and gave, after purification
of the crude product by Kugelrohr distillation, 1.02 g (71%) of a mixture
1
13
column DB1, 29 m. H and C NMR spectra were recorded in CDCl
on a Bruker AM 300 or Bruker AM 500 spectrometer at 20 °C using
3
2
D
0
1
of 16 and 17 (≈1:1) as a colorless oil; n ) 1.4500; H NMR (500.1
1
13
TMS ( H NMR) and CDCl (δ ) 77.0 ppm, C NMR) as internal
3
3 2
MHz) δ ) 0.79 (d, J ) 6.6 Hz, 6H, CH(CH ) ), 0.87 (t, J ) 7.0 Hz,
1
13
standards. Selected data are given; full H and C NMR data are
available from the authors on request. Mass spectra were recorded on
a Finnigan MAT 212. All products were unambiguously identified by
H and C NMR and by MS (EI) or GC/MS (EI). Refractive indices,
, were taken on a Zeiss-Abb e´ refractometer. Elemental analyses were
3
2
H, 18-H), 1.25 (m, 27 H, CH
.29 (t, J ) 7.6, 2H, 2-H), 3.65 (s, 3H, OCH
), 22.66 (C17), 24.94 (C3), 31.91
2
), 1.61 (m, 2H, 3-H), 1.66 (m, 1H, 9-H),
13
3
); C NMR (125.8 MHz)
3 2
δ ) 14.07 (C18), 19.17 (CH(CH )
1
13
CH(CH
3
)
2
), 34.10 (C2), 43.69 (C9(10)), 51.37 (OCH
3
), 174.29 (C1);
n
D
+
MS(EI), m/z (%) 340(10) [M ], 309(2), 297(100), 265(25); C22
H O
44 2
performed by Mikroanalytisches Labor Beller, D-37004 G o¨ ttingen,
Germany.
(340.59) calcd, C 77.58, H 13.02; found, C 77.50, H 12.91.
6. Mixture of Methyl 12-Hydroxy-9-isopropyloctadecanoate (18)
2
. Synthesis of Alkylation Products. 2.1. Procedure 1 (Standard
Reaction Conditions). A mixture of 5 mmol of the respective alkene
and 5 mmol of the alkyl chloroformate, 12, in CH Cl (10 mL) was
stirred in a N atmosphere (1 bar) for 5 min at -15 °C. Et Al Cl (1.24
and Methyl 12-Hydroxy-10-isopropyloctadecanoate (19). The reac-
tion of methyl ricinoleate (4) (1.56 g, 4.2 mmol) and isopropyl
chloroformate (12a) (0.7 g, 5 mmol) was carried out as described
2
2
2
3
2
3
(procedure 1) and gave, after purification of the crude product by
g, 5 mmol for 1, 6, and 9-11; 1.86 g, 7.5 mmol for 2 and 3, and 2.47
g, 10 mmol for 4) was added dropwise over 1h (0.5 h for 6) at -15
Kugelrohr ditillation, 0.9 g (60%) of a mixture of 18 and 19, which
were formed as mixtures of diastereomers, respectively, in a ratio of
°
C, and the solution was stirred at room temperature for an additional
h (0.5 h for 6). Diethyl ether (100 mL), H O (40 mL), and 10% HCl,
to dissolve precipitated aluminum salts, were then added. The organic
phase was separated and washed with H
O (3 × 30 mL). The combined
extracts were dried over Na SO . The solvent was removed in vacuo.
20
7
:1 (GC) for 18 and 5:3 (GC) for 19, as a colorless oil; nD ) 1.4605;
1
2
1
H NMR (500.1 MHz) δ ) 0.82 (m, 9H, 18-H, (CH
2
2
13
3
)
2
CH), 1.23 (m,
), 1.37 (m, 4H, 11-H, 13-H), 1.59 (m, 3H, 3-H, 9(10)-H),
.27 (t, J ) 7.5 Hz, 2H, 2-H), 3.55 (m, 1H, 12-H), 3.64 (s, 3H, OCH );
), 19.05
), 34.05 (C2),
8.32 (C9(10)), 38.57 (C9(10)), 39.80 (C9(10)), 43.80 (C9(10)), 51.36
), 70.11 (C12), 70.41 (C12), 72.39 (C12), 72.44 (C12), 174.27
2H, CH
2
2
3
2
4
C NMR (125.8 MHz) δ ) 14.02 (C18), 18.14 (CHCH
CHCH ), 19.24 (CHCH ), 22.57 (C17), 31.81 (CH(CH
3
Purification was achieved by Kugelrohr distillation or column
chromatography, using petroleum ether/EtOAc (7:3) as eluent. Fractions
containing the alkylation products were collected, the solvent was
evaporated, and the residue was dried at 20 °C/0.01 mbar.
(
3
(
(
3
3
3 2
)
OCH
C1); MS (CI, iso-butane) m/z (%) 357(18) [MH ], 3.39(100) [MH
O]; HR-MS (EI) C22 calcd, 356.3290; found, 356.3293.
. Mixture of 9-Cyclohexyloctadecanoic Acid (20) and 10-
3
+
+
2
.2. Procedure 2 (Modified Reaction Conditions with Addition
of Triethylsilane). A mixture of 5 mmol of the respective alkene and
of 5 mmol of the alkyl chloroformate, 12, in CH Cl (10 mL) was
stirred in a N atmosphere (1 bar) for 5 min at -15 °C. A mixture of
-
H
2
44 3
H O
7
2
2
Cyclohexyloctadecanoic Acid (21). The reaction of oleic acid (2) (1.41
g, 4.2 mmol) and cyclohexyl chloroformate (12b) (0.81 g, 5 mmol)
was carried out as described (procedure 1) and gave, after purification
of the crude product by column chromatography, 1.51 g (83%) of a
2
(
35) Vrcek, V.; Saunders, M.; Kronja, O. J. Org. Chem. 2003, 68, 1859-1866.
(
36) Petersen, S.; Piepenbrink, H.-F. In Houben-Weyl, 4th ed.; Georg Thieme-
Verlag: Stuttgart, 1952; Vol. 8, 101-104.
20
1
mixture of 20 and 21 (≈1:1) as a pale yellow oil; nD ) 1.4712; H
10328 J. AM. CHEM. SOC.
9
VOL. 126, NO. 33, 2004

Alkylation of Alkenes with Ethylaluminum Sesquichloride
A R T I C L E S
NMR (500.1 MHz) δ ) 0.89 (t, J ) 7.1 Hz, 3H, 18-H), 0.95-1.35
14. Mixture of 9-sec-Butyloctadecanoic Acid (32) and 10-sec-
Butyloctadecanoic Acid (33). The reaction of oleic acid (2) (1.42 g,
4.2 mmol) and 1-butyl chloroformate (12e) (0.69 g, 5 mmol) was carried
out as described (procedure 1) and gave, after purification of the crude
product by column chromatography, 1.06 g (74%) of a mixture of 32
(
(
(
m, 32H, CH
2
2
), 1.5-1.80 (m, 8H, 3-H, 9-H, CH-, and CH -cHex), 2.35
1
3
t, J ) 7.7 Hz, 2H, 2-H), C NMR (125.8 MHz) δ ) 14.1 (C18), 34.0
C2), 40.2 (CH-cHex), 43.3 (C9(10)), 179.9 (C1); MS (EI) of the methyl
+
esters of 20 and 21, m/z (%) 380(15) [M ], 349(3), 297(75), 264(22);
20
1
HR-MS (EI) C24
. Isopropylcyclopentane (23). The reaction of cyclopentene (11)
0.68 g, 10 mmol) and isopropyl chloroformate (12a) (1.4 g, 10 mmol)
was carried out as described (procedure 2), using 2.48 g (10 mmol) of
Et Al Cl and 1.16 g (10 mmol) of Et SiH. After purification of the
H O
46 2
calcd, 366.3497; found, 366.3497.
and 33 (≈1:1) as a colorless oil; n ) 1.4580; H NMR (300.1 MHz)
D
δ ) 0.78 (d, J ) 6.7 Hz, 3H, CH
3
CH), 0.88 (2× t, J ) 6.7 Hz, 6H,
8
CH
3
2
CH CH and 18-H), 1.15-1.45 (m, 30H), 1.63 (tt, J ) 7.4, 7.1 Hz,
(
13
2
1
H, 3-H), 2.35 (t, J ) 7.5 Hz, 2H, 2-H); C NMR (75.8 MHz) δ )
3 2
2.3 (CH CH CH), 14.0 (C18) 15.0 (CH
3
CH), 34.0 (C2), 36.3
3
2
3
3
+
3
(CH CH), 42.0 (C9(10)), 180.0 (C1); MS (EI), m/z (%) 340(4) [M ],
crude product by Kugelrohr distillation, 0.77 g (69%) of 23 was
obtained. The product was characterized by GC/MS. As minor products,
cis- (2%, GC) and trans-dimethylcyclohexan (2%, GC) were detected.
44 2
311(5), 283(100), 265(37); C22H O (340.59) calcd, C 77.58, H 13.02;
found, C 77.52, H 12.98.
5. 12-Methyltetradecanoic Acid (34). The reaction of 10-unde-
1
9. Synthesis of 1-Isopropyl-2-methyl-cyclohexane (24). The reac-
cenoic acid (9) (0.92 g, 5 mmol) and 1-butyl chloroformate (12e) (0.68
g, 5 mmol) was carried out as described (procedure 2) and gave, after
purification of the crude product by column chromatography, 0.87 g
tion of 1-methylcyclohexene (6) (0.48 g, 5 mmol) and isopropyl
chloroformate (12a) (0.7 g, 5 mmol) was carried out as described
(
procedure 1) and gave, after purification of the crude product by
Kugelrohr distillation, 0.44 g (49%) of 24 as a diastereomeric mixture
[trans-24]:[cis-24] ) 1.5:1). Trans- and cis-24 were characterized by
2
D
0
13
(
72%) of 34 as a colorless liquid; n ) 1.4528; C NMR (125.8
3
MHz) δ ) 11.38 (C14), 19.20 (CH CH), 31.97 (C13), 34.13 (C12,
(
C2), 36.64 (C11), 180.52 (C1); GC/MS (EI) of the methyl ester of 34,
their MS and NMR data; the latter are in agreement with the
corresponding data given in ref 37.
+
m/z (%) 256(17) [M ], 227(5), 225(5), 199(10), 74(100).
1
6. sec-Butylcyclohexane (35). The reaction of cyclohexene (5)
1.23 g, 15 mmol) and 1-butyl chloroformate (12e) (2.04 g, 15 mmol)
was carried out as described (procedure 2), using 3.72 g (15 mmol) of
Et Al Cl and 1.74 g (15 mmol) of Et SiH. After purification of the
10. 2,4-Dimethyltridecane (26). The reaction of 2-methylundecene
(
(8) (0.84 g, 5 mmol) and isopropyl chloroformate (12a) (0.7 g, 5 mmol)
was carried out as described (procedure 2) and gave, after purification
3
2
3
3
1
of the crude product by Kugelrohr distillation, 0.5 g (47%) of 26; H
crude product by fractionated micro distillation, 0.62 g (30%) of 35
NMR (300.1 MHz) δ ) 0.93 (m, 12H, CH
3
), 1.04 (m, 1H, 3-H
), 1.52 (m, 1H, 4-H), 1.71 (qqt, J ) 6.8, 6.6, 6.6 Hz, 1H,
-H); C NMR (75.5 MHz) δ ) 14.13 (C13), 19.85 (CHCH ), 22.35
), 23.48, 25.31, 27.09, 29.46, 29.76, 29.84, 30.13,
0.36, 32.02 (C2), 37.54 (C3), 46.97 (C4); C15 32 (212.42) calcd, C
4.80, H 15.18; found, C 84.90, H 15.20. In addition, 10,10,13-
a
), 1.18
+
was obtained. GC/MS (EI) of 35, m/z (%) 140(27) [M ], 111(37), 83-
(
2
s, 16H, CH
2
(100), 69(32). Additional cyclohexylcyclohexane (0.45 g, 40%) was
1
3
3
formed. Mixtures of 2-pentylcyclohexane (36) and 3-pentylcyclohexane
3 2
and 22.77 (CH(CH )
3
8
(
(
37) in a ratio of [36]:[37] ) 1.3:1 (GC), as well as 2-hexylcyclohexane
38) and 3-hexylcyclohexane (39) in a ratio of [38]:[39] ) 1:1(GC),
H
were obtained by analogous reactions with 1-pentyl chloroformate (12f),
-pentyl chloroformate (12l), and 1-hexyl chloroformate (12g), respec-
tively, and were characterized by GC and GC/MS.
7. Mixture of 12-Methylhexadecanoic Acid (40) and 12-Ethyl-
trimethyleicosane (29%, GC) was formed and identified by GC/MS
EI).
1. 12-Methyltridecanoic Acid (27). The reaction of 10-undecenoic
3
(
1
1
acid (9) (0.92 g, 5 mmol) and isopropyl chlorformate (12a) or 1-propyl
chloroformate (12d) (0.7 g, 5 mmol), respectively, was carried out as
described (procedure 2) and gave, after purification of the crude product
by column chromatography, 0.63 g (56%) and 0.68 g (60%) of 27,
respectively, as a solid; mp ) 48-50 °C (ref 38, mp ) 44-48 °C).
pentadecanoic Acid (41). The reaction of 10-undecenoic acid (9) (0.92
g, 5 mmol) and 1-hexyl chloroformate (12g) (0.81 g, 5 mmol) was
carried out as described (procedure 2) and gave, after purification of
the crude product by column chromatography, 0.6 g (44%) of a mixture
20
of 40 and 41 ([40]:[41] ) 1.1:1, GC) as a colorless liquid; nD
)
1
The H NMR spectrum and the mass spectrum (EI) of the methyl ester
of 27 were in agreement with data given in refs 38 and 39.
1
.4637; GC/MS (EI) of the methyl esters of 40 and 41 (the mass
spectrum of the methyl ester of 40 was in agreement with the
+
1
2. 11-Cyclohexylundecanoic Acid (29). The reaction of 10-
undecenoic acid (9) (0.92 g, 5 mmol) and cyclohexyl chloroformate
12b) (0.81 g, 5 mmol) was carried out as described (procedure 2) and
gave, after purification of the crude product by column chromatography,
.78 g (58%) of 29 as a solid; mp ) 35-37 °C. The GC and MS data
of the methyl ester of 29 were in agreement with those given in ref 3.
3. Mixture of 12-Methylpentadecanoic Acid (30) and 12-
Ethyltetradecanoic Acid (31). The reaction of 10-undecenoic acid (9)
0.92 g, 5 mmol) and 2-pentyl chloroformate (12c) (0.75 g, 5 mmol)
corresponding data given in ref 40); 41, m/z (%) 284(40) [M ], 253(5),
241(24), 199(50); C H O (270.44) calcd, C 75.49, H 12.57; found,
17
34
2
(
C 75.03, H 12.89.
18. Mixture of 12-Methyltetradecanoic Acid (34) and 11,12-
Dimethyltridecanoic Acid (44). The reaction of 10-undecenoic acid
(9) (0.92 g, 5 mmol) and isobutyl chloroformate (12h) (0.68 g, 5 mmol)
was carried out as described (procedure 1) and gave, after purification
of the crude product by column chromatography, 0.79 g (65%) of a
0
1
2
D
0
(
mixture of 34 and 44 ([34]:[44] ) 1:2.2, GC) as a colorless liquid; n
) 1.4513.
was carried out as described (procedure 2) and gave, after purification
of the crude product by column chromatography, 0.92 g (72%) of a
19. Mixture of sec-Butylcyclohexane (35), 1-Methyl-1-isopropyl-
cyclohexane (45), and tert-Butylcyclohexane (54). The reaction of
cyclohexene (5) (0.82 g, 10 mmol) and isobutyl chloroformate (12h)
(1.28 g, 10 mmol) was carried out as described (procedure 1), using
2
D
0
mixture of 30 and 31 ([30]:[31] ) 1.2:1, GC) as a pale yellow oil; n
)
1
1.4628; H NMR (300.1 MHz) δ ) 0.75-0.9 (m, 6H, 2× CH
.1-1.4 (m, 23H, CH , CH(30)), 1.50 (m, 1H, CH(31)), 1.63 (tt, J )
.4, 7.2 Hz, 2H, 3-H), 2.34 (t, J ) 7.2 Hz, 2H, 2-H); C NMR (75.8
, 31), 14.1 (CH , C15), 19.6 (CH CH), 32.4 (C12,
0), 34.3 (C2, 30 and 31), 40.1 (C12, 31), 180.4 (C1, 30 and 31); GC/
3
),
1
7
2
1
3
3 2 3
2.48 g (10 mmol) of Et Al Cl . After purification of the crude product
MHz) δ ) 10.9 (CH
3
3
3
by fractionated micro distillation, 0.58 g (41%) of a mixture of 35, 45,
and 54 was obtained in a ratio of [35]:[45]:[54] ) 12.5:2.5:1 (GC).
The mass spectra (EI) of 45 and 54 were in agreement with the
published spectra (NIST Chemistry Web Book; NIST Standard Reference
Database Number 69, March, 2003 Release; EPA MS numbers 158552
and 230537, respectively).
3
+
MS (EI) of the methyl esters of 30 and 31; 30, m/z (%) 270(15) [M ],
+
2
27(15); 31, m/z (%) 270(20) [M ], 241(30); C16
H
32
O
2
(256.43) calcd,
C 74.92, H 12.58; found, C 75.07; H 12.21
2
0. Mixture of 11,12-Dimethyltetradecanoic Acid (46) and 11-
(
37) Bazyl’chik, V. V.; Samitov, Y. Y.; Ryabushkina, N. M. J. Appl. Spectrosc.
1
980, 32(5), 543-548.
Ethyl-12-methyltridecanoic Acid (47). The reaction of 10-undecenoic
(38) Balzer, T.; Budzikiewicz, H. Z. Naturforsch. 1987, 42b, 1367-1368.
(
39) Goodrich, B. S.; Roberts, D. S. Aust. J. Chem. 1971, 24, 4, 153-159.
(40) Jacob, J.; Zeman, A. Z. Naturforsch. 1970, 25b, 1438-1447.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 33, 2004 10329

A R T I C L E S
Biermann and Metzger
acid (9) (0.92 g, 5 mmol) and neopentyl chloroformate (12i) (0.75 g,
h at room temperature. Further work up was carried out as described
(procedure 2). Column chromatography (petroleum ether/EtOAc (7:
5
mmol) was carried out as described (procedure 1) and gave, after
purification of the crude product by column chromatography, 0.89 g
70%) of a mixture of 46 and 47 ([46]:[47] ) 2.2:1, GC) as colorless
20
13
3)) gave 0.72 g (60%) of 44 as a colorless oil; n ) 1.4605; C NMR
D
(
3 3 2 3 2
(125.8 MHz) δ ) 15.35 (CH CH), 17.97 (CH ) CH), 20.25 (CH ) -
2
0
liquid; n ) 1.4541. 46 was formed as a diastereomeric mixture in a
ratio of approximately 1:1( C NMR); GC/MS(EI) of the methyl esters
of 46 and 47; 46, m/z (%) 270(39) [M ], 255(1), 241(17), 239(8),
CH), 34.13 (C2 and C12), 34.40 (C10), 38.53 (C11), 180.52 (C1); GC/
D
13
+
MS (EI) of the methyl ester of 44, m/z (%) 256(37) [M ], 241(2),
+
225(8), 213(86), 181(29), 74(100); C15
H 12.48; found, C 74.70, H 12.10.
30 2
H O (242.40) calcd, C 74.30,
+
213(100), 181(36); 47, m/z (%) 270(17) [M ], 241(9), 239(3), 227(100),
1
32 2
95(23); C16H O (256.43) calcd, C 74.94, H 12.58; found, C 74.78,
2
5. 2,2,4-Trimethyltetradecane (53). A mixture of 2-methyl-1-
undecene (8) (0.84 g, 5 mmol) and di-tert-butylpyrocarbonate (52) (0.77
g, 3.5 mmol) in CH Cl (10 mL) was stirred in a N atmosphere (1
bar) for 10 min at -15 °C. A mixture of Et Al Cl (1.24 g, 5 mmol)
and Et SiH (0.58 g, 5 mmol) was then added dropwise over 1 h at
15 °C, and the mixture was stirred for an additional 1 h at room
H 12.72.
1. Mixture of 1-Ethyl-1-isopropylcyclohexane (48) and 1-sec-
2
2
2
2
Butyl-1-methylcyclohexane (49). The reaction of cyclohexene (5) (0.41
g, 5 mmol) and neopentylbutyl chloroformate (12i) (0.75 g, 5 mmol)
was carried out as described (procedure 1) and gave, after purification
of the crude product by Kugelrohr distillation, 0.65 g (84%) of a mixture
of 48 and 49 ( [48]:[49] ) 1.3:1, GC). GC/MS (EI) of 48 and 49; 48,
3
2
3
3
-
temperature. Further work up was carried out as described (procedure
). Kugelrohr distillation (70 °C, 8 mbar) gave 0.48 g (43%) of a
colorless liquid, nD ) 1.4349; H NMR (500.1 MHz) δ ) 0.87 (m,
H, 13-H), 0.88 (s, 9H, 1-H, C(CH
dd, J ) 13.7, 6.3 Hz, 1H, 3-H), 1.21 (dd, J ) 13.7, 3.4 Hz, 1H, 3-H′),
.43 (m, 1H, 4-H), 1.30-1.21 (m, 16H, 5-12-H); C NMR (125.8
MHz) δ ) 14.1 (C1), 22.7 (C12, C14), 29.4-30.0 (C7-10), 30.0 (C1),
1.1 (C2), 34.0 (C4), 39.7 (C5), 51.4 (C3); HR-MS (EI) C16
-3
2
+
20
m/z (%) 154(5) [M ], 125(9), 111(100), 83(33), 69(77); 49, m/z (%)
1
+
1
54(1) [M ], 97(100), 69(8).
3
3 2 3
) ), 0.89 (m, 3H, CH(CH )), 1.01
22. Mixture of 1-Ethyl-1,2-dimethylcyclohexane (50) and 1-Ethyl-
(
1
2,2-dimethylcyclohexane (51). The reaction of cyclopentene (11) (0.34
13
g, 5 mmol) and neopentylbutyl chloroformate (12i) (0.75 g, 5 mmol)
was carried out as described (procedure 1) and gave, after purification
of the crude product by Kugelrohr distillation, 0.46 g (65%) of a mixture
of 50 and 51 ([50]:[51] ) 2.8:1 (GC). Compound 50 was formed as a
3
H34 calcd,
2
26.2660; found, 226.2660.
2
6. Mixture of 1-Isopropyl-1-methylcyclohexane (45) and tert-
Butylcyclohexane (54). A mixture of cyclohexene (5) (0.41 g, 5 mmol)
and di-tert-butylpyrocarbonate (52) (0.77 g, 3.5 mmol) in CH Cl (10
mL) was stirred in a N atmosphere (1 bar) for 10 min at -18 °C.
Et Al Cl (1.24 g, 5 mmol) was then added dropwise over 2 h at -18
C, and the mixture was stirred for an additional 1 h at room
temperature. Further work up was carried out as described (procedure
). Kugelrohr distillation (120 °C, 1013 mbar) gave 0.50 g (71%) of a
1
:1 mixture of diastereomers. GC/MS (EI) of 50 and 51; 50, m/z (%)
+
1
40(1) [M ], 125(3), 111(100), 83(19), 69(87); 51, m/z (%) 140(34)
2
2
+
[M ], 125(42), 111(12), 97(14), 83(22), 69(100).
2
2
3. Mixture of 9-tert-Butyloctadecanoic Acid (42) and 10-tert-
Butyloctadecanoic Acid (43). A mixture of oleic acid (2) (0.72 g, 2.1
mmol) and di-tert-butylpyrocarbonate (52) (0.55 g, 2.5 mmol) in CH
Cl (10 mL) was stirred in a N atmosphere (1 bar) for 10 min at -15
C. Et Al Cl (0.62 g, 2.5 mmol) was then added dropwise over 1 h at
15 °C, and the orange solution was stirred at room temperature for
an additional 1 h. The reaction mixture was worked up as described
3
2
3
°
2
-
2
2
1
°
-
3
2
3
mixture of 45 and 54 in a ratio of [45]:[54] ) 4.7:1 (GC) as a colorless
liquid.
2
7. 1,1,2-Trimethylcyclohexane (55). A mixture of cyclopentene
(procedure 1). Purification of the regioisomeric mixture of 42 and 43
4
1
(11) (0.34 g, 5 mmol) and di-tert-butylpyrocarbonate (52) (0.55 g, 2.5
mmol) in CH Cl (10 mL) was stirred in a N atmosphere (1 bar) for
0 min at -18 °C. Et
over 2 h at -18 °C, and the mixture was stirred for an additional 1 h
at room temperature. Further work up was carried out as described
procedure 1). Kugelrohr distillation (130 °C, 1013 mbar) gave 0.38 g
(60%) of a colorless liquid. The mass spectrum (EI) of 55 was in
agreement with the published spectrum (NIST Chemistry Web Book;
NIST Standard Reference Database Number 69; March, 2003 Release;
EPA MS number 114157).
(1:1) was achieved by treatment of the crude oil with urea and gave
2
D
0
1
2
2
2
0
.69 g (81%) as a pale yellow oil; n ) 1.4705; H NMR (300.1
1
Al Cl
3 2 3
(1.24 g, 5 mmol) was then added dropwise
MHz) 0.7-0.95 (m, 12H, 18-H, (CH
m, 3H, 3-H, 9-H), 2.43 (t, J ) 7.5 Hz, 2H, 2-H); C NMR (75.8
MHz) δ ) 14.1 (C18), 24.4 (CH ), 39.5 (C(CH ), 40.6 (C9(10)),
79.8 (C1); MS(EI) was obtained from the methyl esters of 43/44, m/z
3
)
3
2
), 1.0-1.4 (m, 26H, CH ), 1.62
1
3
(
3
)
3
3 3
)
(
1
+
(
%) 354(10) [M ], 339(100); HR-MS (EI) C22
found, 340.3337.
4. Synthesis of 11,12-Dimethyltridecanoic Acid (44). A mixture
of 10-undecenoic acid (9) (0.92 g, 5 mmol) and di-tert-butylpyrocar-
bonate (52) (1,0 g, 5 mmol) in CH Cl (10 mL) was stirred in a N
atmosphere (1 bar) for 10 min at -15 °C. A mixture of Et Al Cl (1.48
g, 6 mmol) and Et SiH (0.58 g, 5 mmol) was then added dropwise
over 1 h at -15 °C, and the mixture was stirred for an additional 1.5
44 2
H O calcd, 340.3341;
2
2
2
2
Acknowledgment. This work was financially supported by
the German Research Foundation (DFG, ME 722/14-1). We
thank Dr. Arne L u¨ tzen, University of Oldenburg, for helpful
discussion of NMR spectra.
3
2
3
3
(41) Schlenk, W. In Houben-Weyl, 4th ed.; Georg Thieme-Verlag: Stuttgart,
1
958; Vol 1/1, p 391.
JA048904Y
10330 J. AM. CHEM. SOC.
9
VOL. 126, NO. 33, 2004