Reductive cleavage versus hydrogenation of allyl aryl ethers and allylic esters using sodium borohydride/catalytic ruthenium(III) in various aqueous solvent mixtures

Article abstract of DOI:10.1016/j.tetlet.2010.12.023

The reduction of allyl aryl ethers using sodium borohydride in the presence of a catalytic amount of ruthenium(III) chloride in various aqueous solvent mixtures at 0 °C was examined. In aqueous tetrahydrofuran, hydrogenation was the favored pathway (85-100% yield of the corresponding aryl propyl ether); whereas in aqueous N-methylformamide, reductive cleavage predominated (4:1 mixture of phenolic product/aryl propyl ether). In order to gain some insight into the mechanism for this process, 3-octyn-1-ol and trans-2-decen-1-yl acetate were subjected to similar reductive conditions; and both substrates afforded products inconsistent with a single-electron-transfer mechanism.

Full text of DOI:10.1016/j.tetlet.2010.12.023

Tetrahedron Letters 52 (2011) 745–748
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Reductive cleavage versus hydrogenation of allyl aryl ethers and allylic
esters using sodium borohydride/catalytic ruthenium(III) in various
aqueous solvent mixtures
⇑
James H. Babler , Nicholas A. White, Eric Kowalski, Jeffrey R. Jast
Department of Chemistry, Loyola University Chicago, Chicago, IL 60660, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The reduction of allyl aryl ethers using sodium borohydride in the presence of a catalytic amount of
ruthenium(III) chloride in various aqueous solvent mixtures at 0 °C was examined. In aqueous tetrahy-
drofuran, hydrogenation was the favored pathway (85–100% yield of the corresponding aryl propyl
ether); whereas in aqueous N-methylformamide, reductive cleavage predominated (4:1 mixture of
phenolic product/aryl propyl ether). In order to gain some insight into the mechanism for this process,
3-octyn-1-ol and trans-2-decen-1-yl acetate were subjected to similar reductive conditions; and both
substrates afforded products inconsistent with a single-electron-transfer mechanism.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 13 August 2010
Revised 2 December 2010
Accepted 6 December 2010
Available online 10 December 2010
Recently we reported1 an experimentally convenient process
for the small-scale hydrogenation of alkenes that avoids the use
of a hydrogen cylinder and pressure equipment. The chemoselec-
tive reduction of various types of functionalized alkenes (including
trisubstituted olefins) was achieved by addition of one molar
equivalent (or less) of sodium borohydride to an aqueous
N,N-dimethylacetamide (DMA) solution of the substrate and a
catalytic amount of ruthenium(III) chloride at 0 °C, followed by
subsequent stirring of this mixture in a stoppered flask at 0 °C
for 60 min. Similar conditions (NaBH4/cat. RuCl3) had previously
been reported2 for selective reduction of mono- and disubstituted
olefins in aqueous tetrahydrofuran (THF); however, that process
resulted in a rapid evolution of hydrogen, loss of color in the liquid
phase, and proceeded very slowly at 0 °C. In sharp contrast, when
similar reductions were conducted in aqueous DMA, we observed1
little (if any) release of H2 and the appearance of a long-lasting
(usually 30 min or more) dark blue-green color3 (sometimes, very
dark brown) in the liquid phase. In view of the unexpected behav-
ior of the reductant in aqueous DMA (vs aqueous THF2), we
decided to investigate this process further to obtain insight into a
mechanistic pathway and to extend its synthetic utility.
(<15%) of phenyl propyl sulfone was obtained—an indication that
reductive cleavage may have occurred. Since alcohols, phenols,
and carboxylic acids can be protected5 by conversion to the corre-
sponding allyl ethers and esters, we decided to investigate our con-
ditions (NaBH4/cat. Ru+3/aqueous DMA) as a possible method for
deblocking such allyl derivatives. Although NaBH4/cat. Ru+3/3:1
(v/v) THF/H2O has been reported2 to convert allyl phenyl ether to
phenyl propyl ether in quantitative yield, we hoped that our condi-
tions would be more robust and effect the reductive cleavage of
various types of allyl derivatives. Such a process could then be use-
ful in protective group chemistry since various sensitive and/or
reducible groups (e.g., acetals, allylic alcohols, benzyl ethers, epox-
ides, esters, halides, nitriles, and sulfones) have been shown1 to be
inert to these reducing conditions.
To initiate this study, we selected 1-methyl-4-(2-propen-1-
yloxy)benzene (1a)6 (allyl 4-methylphenyl ether) to ascertain
whether our conditions (NaBH4/cat. RuCl3/aqueous DMA) would
result in any reductive cleavage7 of this allyl moiety along with
the expected2 hydrogenation of the allyl group. When the latter
ether (1a) was subjected to our general procedure8 [using 10:1
(v/v) DMA/H2O as the solvent], proton NMR analysis9 of the
isolated product mixture indicated the presence of only two
components: 4-methylphenol (2a)10 and 1-methyl-4-propoxyben-
zene (3a)11 in a ratio of 55:45. Although reductive cleavage of the
allyl aryl ether was slightly favored over hydrogenation of the ole-
fin functionality, the recovery of material was only 60%—presum-
ably due to the loss of a substantial amount of 4-methylphenol
(2a) during the aqueous washes used in the product isolation
procedure.
Our previous Letter1 reported that the sulfone functionality was
inert to NaBH4/cat. RuCl3 in aqueous DMA at 0 °C; however, during
that study, in an attempt to reduce the olefin moiety in allyl phenyl
sulfone4 using the latter conditions, only a low isolated yield
⇑
Corresponding author.
E-mail address: jbabler@luc.edu (J.H. Babler).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.12.023

746
J. H. Babler et al. / Tetrahedron Letters 52 (2011) 745–748
O
R
OH
O
R
NaBH4/cat. RuCl3
+
solvent, 0 °C, 60 min
(1)
R'
R
R'
R'
1
3
2
a, R = H; R' = CH3
b, R = CH(CH3)2 ; R' = H
c, R = Br ; R' = CH3
In order to determine more accurately the feasibility of effecting
from our previous work,1 benzyl ether4 and alkyl aryl ethers (e.g.,
reductive cleavage of an allyl aryl ether (rather than hydrogenation
of the allyl moiety), we selected 1-(1-methylethyl)-2-(2-propen-1-
yloxy)benzene (1b)12 as the representative substrate and con-
ducted an investigation of the effect various solvent mixtures
had on the ratio of the two expected products (2b and 3b13). As
indicated by the results in Table 1, a wide variation in the product
ratio can be obtained as the organic solvent in the aqueous reaction
mixture is changed from tetrahydrofuran (which afforded predom-
inantly hydrogenation product 3b) to the more polar liquid carbox-
amides, especially the protic, highly polar N-methylformamide,
which dramatically enhanced the rate of cleavage (1b ? 2b).
Decreasing the water content of the mixture (Table 1, entry 3 vs
entry 1) also favored reductive cleavage of the allyl ether.
1-ethoxy-3-methylbenzene17
procedure.
)
were inert to this reductive
To our surprise, subjection of a simple alkyl allyl ether to the
general procedure for reductive cleavage [10:1 (v/v) N-methylfor-
mamide/H2O as the solvent] occurred slowly and with poor selec-
tivity. Thus, allyl octyl ether18 [1-(2-propen-1-yloxy)octane]
afforded, after approximately 50% conversion, a 3:2 mixture of oc-
tyl propyl ether19/1-octanol. In order to increase the solubility of
allyl octyl ether in the reaction mixture, this procedure was re-
peated using 10:1 (v/v) DMA/H2O as the solvent; and, to our dis-
may, >80% of the isolated product was 1-propoxyoctane19 (octyl
propyl ether), the product derived from hydrogenation of the allyl
moiety.
To verify the stability of a halide functionality to the conditions
used in this reductive methodology, the allyl ether derivative (1c)
[2-bromo-4-methyl-1-(2-propen-1-yloxy)benzene14] of 2-bromo-
4-methylphenol4 was subjected to the general procedure8 [using
10:1 (v/v) N-methylformamide/H2O as the solvent] and afforded
a 77% isolated yield of the deblocked 2-bromo-4-methylphenol
(2c)10 and the hydrogenation product (2-bromo-4-methyl-1-prop-
oxybenzene (3c)15) in a 4:1 ratio,16 respectively. As expected
The reductive cleavage process was successful when applied to
a representative allyl ester (allyl nonanoate); although, as ex-
pected, benzyl esters (e.g., benzyl octanoate20) and alkyl esters
(e.g., octyl acetate4) were inert to such conditions. Subjection of al-
lyl nonanoate21 to the general procedure8 [using 10:1 (v/v) DMA/
H2O to dissolve this fatty ester] afforded cleanly a 4:1 mixture22
of nonanoic acid/propyl nonanoate,23 respectively, in 90% yield
[isolated yield (reduction products + starting material) 94%].
Table 1
Ru+3-catalyzed reductiona of 1-(1-methylethyl)-2-(2-propen-1-yloxy)benzeneb (1b) using NaBH4 in various aqueous solvent mixtures
Entry
Solvent Mixture
Recovery [product(s) +
unreacted substrate] (%)
Isolated yield of
reduction products (%)
Ratioc,d of
O
OH
:
(3b)
(2b)
1
2
3
4
5
6
7
8
9
0.60 mL of 5:1 (v/v) DMAe/H2O
74
81
70
73
92
93
93
98
83
74
81
60
63
92
93
93
98
37
65:35
2:1
1:4
1.1:1
3:1
4:1
3:1
1:5
4:5
0.60 mL of 5:1 (v/v) CH3NHCH@O/H2O
0.75 mL of 2:1 (v/v) DMA/H2Of
0.75 mL of 2:1 (v/v) CH3NHCH@O/H2O
0.50 mL of 5:5:1 (v/v/v) DMA/CH3NHCH@O/H2O
0.50 mL of 10:1 (v/v) CH3NHCH@O/H2O
0.50 mL of 25:1 (v/v) CH3NHCH@O/H2O
0.60 mL of 5:1 (v/v) THF/H2Og
0.60 mL of 5:1 (v/v) CH3CN/H2Oh
a
All reactions were conducted at 0 °C by addition of NaBH4 (0.24 mmol) to an aqueous solvent mixture of substrate ether (0.19–0.20 mmol) and ruthenium(III) chloride
hydrate (0.034 mmol), using the general procedure8 for reductive cleavage of allyl ethers and esters.
b
Prepared in 98% yield by reaction of 2-isopropylphenol (2b) [commercially available from Sigma–Aldrich (Milwaukee, WI, USA)] with allyl bromide in acetone containing
12
an excess of K2CO3 powder at 20 °C. For a previous synthesis of this allyl ether, see Ref.
.
c
Structural assignments and product ratios were based on analysis of 1H NMR spectral data (300 MHz) for these known compounds. For a previous synthesis of 1-(1-
13
methylethyl)-2-propoxybenzene (3b), see Ref.
.
d
The 1H NMR spectrum (300 MHz, CDCl3) of 2-isopropylphenol (2b) was characterized by signals at d 4.72 (s, 1H, OH); 3.21 (septet, J = 6.9 Hz, 1H); and 1.26 (d, J = 6.9 Hz,
6H). 1-(1-Methylethyl)-2-propoxybenzene (3b) was characterized by signals at d 3.92 (t, J = 6.6 Hz, 2H, CH2O); 3.35 (septet, J = 6.9 Hz, 1H); 1.21 (d, J = 6.9 Hz, 6H); and 1.06 (t,
J = 7.2 Hz, 3H). Unless indicated otherwise, no unreacted starting ether (1b) [characterized by a signal at d 4.53 (dt, J = 5.1 and 1.5 Hz, 2H, CH2O)] was detected in the isolated
product mixture.
e
Similar results were obtained when DMA was replaced by DMF, NMP, or DMPU [1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone].
f
The quantities of NaBH4 and RuCl3ÁxH2O were decreased to 0.18 mmol and 0.019 mmol, respectively, in this experiment.
g
This experiment, which involved the rapid evolution of H2 gas upon addition of NaBH4 to the mixture, occurred more slowly than reactions conducted in aqueous
carboxamides. For consumption of all starting allyl ether, the reaction mixture was stirred in a closed vessel at 0 °C for 60 min, followed by 150 min at 20 °C.
h
This experiment occurred more slowly than reactions conducted in aqueous carboxamides. The reaction mixture was stirred at 0 °C for 40 min, followed by 75 min at
20 °C. Since the selectivity (reductive cleavage versus hydrogenation) was not encouraging, no attempt was made to repeat this experiment to determine if all starting allyl
ether could be consumed.

J. H. Babler et al. / Tetrahedron Letters 52 (2011) 745–748
747
In order to elucidate a mechanistic pathway for this reductive
cleavage process, 3-octyn-1-ol4 was subjected to similar reaction
conditions (NaBH4, cat. RuCl3, aqueous DMA, 0 °C). The experimen-
tal conditions were modified to minimize complete reduction of
the alkyne moiety in order to ascertain the stereochemistry of
the initially-formed alkenol. With this goal in mind, 3-octyn-1-ol
(0.20 mmol) in 0.60 mL of 5:1 (v/v) DMA/H2O was reduced at
0 °C (60 min) using only 3.5 mg (0.10 mmol) of NaBH4 in the pres-
ence of 7 mg of RuCl3ÁH2O.4 Isolation of the product in the manner
described in the general procedure8 afforded a 73% isolated yield of
a mixture of three components shown by careful proton NMR anal-
ysis24 to be a 2.5:1:1 mixture of unreacted 3-octyn-1-ol10/(Z)-3-oc-
ten-1-ol25/1-octanol,10 respectively. The most significant result of
the experiment was the failure to detect the presence of any (E)-
3-octen-1-ol,24 thereby excluding a mechanism involving the for-
mation of a radical anion intermediate.
conditions are mild and compatible with many common func-
tional groups.
References and notes
1. Babler, J. H.; White, N. A. Tetrahedron Lett. 2010, 51, 439–441.
2. Sharma, P. K.; Kumar, S.; Kumar, P.; Nielsen, P. Tetrahedron Lett. 2007, 48, 8704–
8708.
3. Reducing agents such as NaBH4 have been reported to convert RuCl3 to a deep
blue colored solution [attributed to the formation of ruthenium(II) chloride
complexes]. These blue complexes are more accurately described as
a
ruthenium(II,III) cluster, which probably involves chloride bridges. See:
Dumas, P. E.; Mercer, E. E. Inorg. Chem. 1972, 11, 531–535.
4. Commercially available from Sigma–Aldrich, Milwaukee, WI, USA.
5. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 3rd ed.; John
Wiley & Sons, 1999.
6. This allyl aryl ether (1a) was prepared in 90% yield by treatment of 4-
methylphenol (p-cresol) with allyl bromide and excess potassium carbonate
powder in acetone at 20 °C. Its 1H NMR spectral data (300 MHz) were identical
H
NaBH4/cat. RuCl3
H
C=C
+
CH3(CH2)3C
CCH2CH2OH
CH3(CH2)7OH
5:1 (v/v)
DMA : H2O
0 °C, 60 min
CH3(CH2)3
CH2CH2OH
(2)
3-octyn-1-ol
(Z)-3-octen-1-ol
to those previously reported by: Kong, L.; Lin, Q.; Lv, X.; Yang, Y.; Jia, Y.; Zhou, Y.
Green Chem. 2009, 11, 1108–1111.
7. Reductive deprotection of allyl aryl ethers using the combination of a molar
excess of NaBH4 and a catalytic amount of Pd(PPh3)4 occurs in high yield under
non-hydrolytic conditions at 20 °C. See: Beugelmans, R.; Bourdet, S.; Bigot, A.;
Zhu, J. Tetrahedron Lett. 1994, 35, 4349–4350.
The unlikelihood of a single-electron-transfer mechanism was
further confirmed by subjection of trans-2-decen-1-yl acetate
(4)26 to our general procedure8 for reductive cleavage in order to
ascertain what happens to the allylic moiety during this transfor-
mation. When the reaction was conducted in 10:1 (v/v) DMA/
H2O using the general procedure,8 the reduction occurred rapidly
(less than 10% allylic acetate 4 was recovered). However, over-
reduction of the initial C-10 alkene product(s) was a serious prob-
lem; and the major product was decane, accompanied by decyl ace-
tate (5).27 To circumvent this problem of over-reduction, the
process was conducted in 5:1 (v/v) N-methylformamide/H2O (in
which any initially-formed 1- and/or 2-decene would be insoluble,
thereby minimizing subsequent reduction). Isolation of the product
mixture using a modified procedure,28 followed by careful proton
NMR analysis of the mixture and comparison of the data with that
exhibited by authentic samples of 1-decene,4 trans-2-decene,29 de-
cyl acetate (5),27 and starting allylic acetate 4, indicated that unre-
acted allylic acetate 4 comprised approximately 50% of the isolated
product mixture. The reduction products consisted of a 2.5:1:1
mixture of trans-2-decene/1-decene/decyl acetate (5), respectively.
The formation of a mixture of both trans-2-decene and 1-decene
8. General procedure for reductive cleavage of allylic ethers and esters: To a 15-
mL 1-neck reaction flask fitted with a glass stopper [NOTE: A larger-scale
reaction may require use of a pressure vessel and/or addition of NaBH4 in small
portions.] were added a small spin bar, 0.19–0.20 mmol of substrate, 0.50 mL of
either 10:1 (v/v) N-methylformamide/H2O or 10:1 (v/v) DMA/H2O, and 7.0 mg
(0.034 mmol) of ruthenium(III) chloride hydrate (Sigma–Aldrich catalog no.
206229). After cooling the latter mixture to 0 °C (external ice-H2O bath), 9.0 mg
(0.24 mmol) of NaBH4 powder was added in one portion; and the mixture was
subsequently stirred at 0 °C for 60 min. The reaction was then quenched by
addition of 2.00 mL of 2 M aqueous HCl to the reaction flask and subsequent
stirring of the mixture at 0 °C for 15 min. The product was then isolated by
dilution of the reaction mixture with 10 mL of 4:1 (v/v) pentane/
dichloromethane; and the solid material was removed by filtration through a
small pad of Hyflo Super-CelÒ filtering aid. After dilution of the filtrate with
20 mL of 9:1 (v/v) pentane/dichloromethane, removal of the amide solvent was
accomplished by washing the organic filtrate with 15% (w/v) aqueous NaCl
(4 Â 20 mL portions). The organic layer was then dried over anhydrous MgSO4,
filtered, and the volatile organic solvents were removed by evaporation at
reduced pressure.
9. This ratio was determined by integration of proton NMR signals (CDCl3,
300 MHz, ppm) arising from 4-methylphenol (2a)10 [d 4.74 (s, 1H, OH)] and 1-
methyl-4-propoxybenzene (3a)11 [d 3.89 (t, J = 6.6 Hz, 2H, CH2O) and d 1.02 (t,
J = 7.2 Hz, 3H)]. For full spectral characterization (1H NMR and 13C NMR) of 4-
methylphenol, see Ref. 10.
during the reductive cleavage suggests the involvement of a p-ally-
lruthenium complex in this process, which is consistent with our
10. The full 1H NMR spectral data of this compound are freely accessible via the
Spectral Data Base System (SDBS) maintained by the Japanese National
observations from two separate control experiments.30
O
NaBH4/cat. RuCl3
trans-2-decene/1-decene
+
CH3CO(CH2)9CH3
(20% of the reduction
O
(2.5/1 ratio)
5:1 (v/v) CH3NHCH=O : H2O
product mixture)
(3)
O
0 °C, 60 min
4
5
Institute of Advanced Industrial Science and Technology at: http://
riodb01.ibase.aist.go.jp/sdbs/cgi-bin/cre_index.cgi?lang=eng.
11. For access to the 1H NMR spectrum of 1-methyl-4-propoxybenzene (3a), see:
Manbeck, G. F.; Lipman, A. J.; Stockland, R. A., Jr.; Freidl, A. L.; Hasler, A. F.;
Stone, J. J.; Guzei, I. A. J. Org. Chem. 2005, 70, 244–250.
12. Marvell, E. N.; Richardson, B.; Anderson, R.; Stephenson, J. L.; Crandall, T. J. Org.
Chem. 1965, 30, 1032–1035.
13. For a previous synthesis of 1-(1-methylethyl)-2-propoxybenzene (3b), see:
Sowa, F. J.; Hinton, H. D.; Nieuwland, J. A. J. Am. Chem. Soc. 1932, 54, 3694–
3698.
In addition to the mechanistic insight presented in this Let-
ter, the reductive methodology detailed herein could be useful
for deblocking allyl aryl ethers in the presence of benzylic
and alkyl aryl ethers, especially if the selectivity (i.e., hydrogen-
olysis vs hydrogenation of the allyl moiety) can be improved.
Selective cleavage of allyl carboxylate esters in the presence
of benzylic, methyl, tert-butyl, and most other types of esters
could also be a useful transformation since the non-hydrolytic

748
J. H. Babler et al. / Tetrahedron Letters 52 (2011) 745–748
14. Prepared in 99% yield by treatment of 2-bromo-4-methylphenol (2c) with allyl
bromide and excess K2CO3 in acetone at 20 °C. For a previous synthesis of this
allyl aryl ether (1c), see: Bradsher, C. K.; Reames, D. C. J. Org. Chem. 1978, 43,
3800–3802.
proton NMR spectrum25 (CDCl3, 400 MHz) of which exhibits a multiplet at d
5.84–5.48 ppm (vinyl H at C-3)].
25. Complete 1H NMR spectral data (CDCl3, 400 MHz) for both (E)- and (Z)-3-
octen-1-ol can be found in: Kapeller, D. C.; Brecker, L.; Hammerschmidt, F.
Chem. Eur. J. 2007, 13, 9582–9588. The signals for the vinyl hydrogens in (Z)-3-
octen-1-ol are listed in the latter publication at d 5.58–5.48 (m, 1H) and 5.40–
5.29 ppm (m, 1H).
15. Holmberg, G. A. Acta Chem. Scand. 1956, 10, 594–598.
16. This ratio was determined by integration of proton NMR signals (CDCl3,
300 MHz, ppm) arising from 2-bromo-4-methylphenol10 [d 7.27 (broad s, 1H, H
at C-3) and d 5.32 (s, 1H, OH)] and 2-bromo-4-methyl-1-propoxybenzene (3c)
[d 7.35 (broad s, 1H, aryl H at C-3); 3.95 (t, J = 6.6 Hz, 2H, CH2O); 2.26 (s, 3H);
1.84 (m, 2H); and 1.06 (t, J = 7.2 Hz, 3H)]. No unreacted allyl aryl ether (1c) was
detected in the product mixture.
17. Carpenter, M. S.; Easter, W. M.; Wood, T. F. J. Org. Chem. 1951, 16, 586–617.
18. Nakagawa, H.; Hirabayashi, T.; Sakaguchi, S.; Ishii, Y. J. Org. Chem. 2004, 69,
3474–3477.
26. Ester
4
was prepared by acetylation of trans-2-decen-1-ol4 using acetic
anhydride in pyridine solution. It was characterized by proton NMR signals
(CDCl3, 300 MHz) at d 5.83–5.71 (m, 1 vinyl H); 5.62–5.50 (m, 1 vinyl H); 4.51
(dd, J = 6.6 and 0.9 Hz, 2H, CH2O); 2.06 (s, 3H); and 0.88 ppm (t, J = 6.9 Hz, 3H).
For a previous synthesis of ester 4, see: Mitsudome, T.; Umetani, T.; Nosaka, N.;
Mori, K.; Mizugaki, T.; Ebitani, K.; Kaneda, K. Angew. Chem., Int. Ed. 2006, 45,
481–485.
19. Devaney, L. W.; Panian, G. W. J. Am. Chem. Soc. 1953, 75, 4836–4837.
20. Murahashi, S.-I.; Naoto, T.; Ito, K.; Maeda, Y.; Taki, H. J. Org. Chem. 1987, 52,
4319–4327.
27. Proton NMR spectral data for decyl acetate can be found in: Sakai, N.; Moriya,
T.; Konakahara, T. J. Org. Chem. 2007, 72, 5920–5922.
28. The product mixture was isolated in the usual manner8 except that, after the
aqueous washes and drying the organic layer over MgSO4, most of the volatile
organic solvents were removed by fractional distillation at atmospheric
pressure (to minimize loss of C-10 alkenes).
21. Allyl nonanoate10 was prepared in 96% yield by treatment of nonanoic acid4
with allyl bromide in the presence of excess potassium carbonate in 2:1 (v/v)
acetone/1-methyl-2-pyrrolidinone at gentle reflux. For a previous synthesis of
this ester, see: Kasymova, S. S.; Ergashev, M. S.; Kulakhmatova, M. A. Uzb. Khim.
Zh. 1982, 6, 63–64.
29. Commercially available from ChemSampCo., Inc., Dallas, TX, USA. trans-2-
Decene was characterized by 1H NMR absorption (CDCl3, 300 MHz) at d 5.47–
5.34 (m, 2H). For a previous synthesis of trans-2-decene, see: Julia, M.; Righini-
Tapie, A.; Verpeaux, J. N. Tetrahedron 1983, 39, 3283–3287.
22. This ratio was determined by 1H NMR analysis of the crude reaction product.
Approximately 4% unreacted allyl nonanoate10 [characterized by a proton NMR
signal (CDCl3, 300 MHz) at d 4.58 (dt, J = 7.7 and 1.2 Hz, 2H, CH2O)] was
detected in the latter mixture. Propyl nonanoate was characterized by proton
NMR signals (CDCl3, 300 MHz, ppm) at d 4.03 (t, J = 6.9 Hz, 2H); 0.94 (t,
J = 7.2 Hz, 3H); and 0.88 (t, J = 6.6 Hz, 3H).
23. Hoback, J. H.; Parsons, D. O.; Bartlett, J. F. J. Am. Chem. Soc. 1943, 65, 1606–
1607.
24. (Z)-3-Octen-1-ol was characterized by proton NMR signals (CDCl3, 300 MHz,
ppm) at d 5.56 (dtt, J = 10.8, 7.2, and 1.5 Hz, 1H, vinyl H at C-3) and 5.36 (dtt,
J = 10.8, 7.2, and 1.5 Hz, 1H, vinyl H at C-4). No absorption was detected in the
region of d 5.85–5.65 ppm [indicative of the presence of (E)-3-octen-1-ol, the
30. As suggested by a reviewer, we conducted a control experiment in which a
solution of allylic acetate 4 (0.20 mmol) and NaBH4 (0.24 mmol) in 0.60 mL of
5:1 (v/v) N-methylformamide/H2O was stirred at 0 °C for 60 min. As expected,
no reduction of unsaturated ester 4 occurred in the absence of ruthenium(III)
chloride. In a separate experiment, a mixture of 1-decene4 (0.20 mmol) and
0.60 mL of 5:1 (v/v) N-methylformamide/H2O containing 4 mg of RuCl3 and
6 mg of NaBH4 powder was stirred at 0 °C for 60 min. Due to its insolubility in
this reaction mixture, 1-decene was reasonably stable under such conditions
[i.e., hydrogenation and isomerization (approximately 5% conversion of 1-
decene to 2-decene occurred) were minimal].