S. Akula et al. / Tetrahedron Letters 53 (2012) 3471–3473
3473
stepwise migration of olefinic function vis-à-vis carbocation to-
ward the carboxylate group till the 4 position, where the nucleo-
philic attack by the carboxyl moiety is facilitated. Gooßen et al.
also proposed similar silver triflate catalyzed shifting of double
bond followed by lactonization. We presume similar mechanistic
pathway for the tandem reaction of unsaturated fatty acid cata-
Supplementary data
D
17
9
lyzed by IL, choline chlorideÁ2ZnCl
2
. In fact, it is the higher complex
References and notes
À
À
zinc chloride ions, [Zn
2
5
Cl ]
and [Zn
3
Cl
7
]
present in the IL which
1
2
.
.
Dufossé, L.; Latrasse, A.; Spinnler, H. –E. Sci. Alim. 1994, 14, 17.
Hislop, J.-A.; Hunt, M. B.; Fielder, S.; Rowan, D. D. J. Agric. Food Chem. 2004, 52,
forms complex with the
p
-cloud of the double bond. The resultant
complex undergoes a series of 1,2-H shift over the carbon chain to-
ward the carboxylate group till 4 position followed by lactoniza-
7
075.
3. Schultt, B.; Moran, N.; Schieberle, P.; Holmann, T. J. Agric. Food Chem. 2007, 55,
634.
D
9
tion to give the desired lactone and releasing the complex zinc
ions. In order to understand the role of complex zinc ions in IL, tan-
dem isomerization–lactonization of UDA was also carried out in a
4
5
.
.
Cermak, S. C.; Isbell, T. A. J. Am. Oil Chem. Soc. 2000, 77, 243.
Ansell, M. F.; Palmer, M. H. J. Chem. Soc. 1963, 2640.
6. Clutterbuck, P. W. J Chem. Soc. 1924, 2330.
solvent-free and IL-free medium by adding anhydrous ZnCl
molar ratio of UDA: ZnCl at 130 °C. After 8 h, about 50% formation
of -undecalactone was observed along with the formation of sev-
2
at 1:1
7. Showell, J. S.; Swern, D.; Noble, W. R. J. Org. Chem. 1968, 66, 2697.
8
9
.
.
Zhou, Y.; Woo, K.; Angelici, R. Appl. Catal., A: General 2007, 333, 238.
Gooßen, L. J.; Ohlmann, D. M.; Dierker, M. Green Chem. 2010, 12, 197–200.
2
c
10. Jain, N.; Kumar, A.; Chauhan, S.; Chauhan, S. M. S. Tetrahedron 2005, 61, 1015.
eral other side products including d-undecalactone. This indicates
increased regiospecificity of the desired product achieved during
the tandem reactions catalyzed by the complex zinc ions present
11. Abott, A.P.; Capper, G.; Davies. D.L.; Munro, H.L.; Rasheed, R.K.; Tambyrajah, V.
Chem. Commun. 2001, 2010.
12. Abott, A. P.; Capper, G.; Davies, D. L.; Rasheed, R. K.; Tambyrajah, V. Green Chem.
2002, 4, 24.
in the IL compared to ZnCl
2
.
13. Morales, R. C.; Tambyrajah, V.; Jenkins, P. R.; Davies, D. L.; Abott, A. P. Chem.
Commun. 2004, 158.
The feasibility of any catalytic process depends on the reusabil-
ity of the catalyst. In the present work, the IL plays the dual role of
solvent as well as catalyst. Recyclability of the IL was studied for
1
1
4. Abott, A. P.; Bell, T. J.; Hand, S.; Stoddart, B. Green Chem. 2005, 7, 705.
5. Duan, Z.; Gu, Y.; Deng, Y. Catal. Commun. 2006, 7, 651.
16. Sunitha, S.; Kanjilal, S.; Reddy, P. S.; Prasad, R. B. N. Tetrahedron Lett. 2007, 48,
962.
7. Granata, A.; Sauriol, F.; Perlin, A. S. Can. J. Chem. 1994, 72, 1684.
8. Preparation of -lactones: (a) -undecalactone: A mixture of 10-undecenylic
acid (2.0 g; 10.8 mmol) and IL (2.23 g; 5.4 mmol) was stirred at 130 °C. After
h, the product was separated from IL by extracting first with ethyl acetate
then with hexane. The organic solvent was evaporated using rotary evaporator
and dried under vacuum to get 1.88 g of peach flavored -undecalactone as
clear oil (isolated yield, 94%). The structure of the product was confirmed by
and 13C NMR, ESI-Mass and matched well with literature report.8 1H NMR
(300 MHz, CDCl , d): 4.46 (tt, 1H, CH–O), 2.51 (dd, 2H, -CH ), 2.31–2.26 (m,
H, b-CH ), 1.90–1.75 (m, 1H, b-CH ), 1.75–1.60 (m, 1H, d-CH ), 1.60–1.50
m,1H, d-CH ), 1.40–1.20 (m, 10H, 5CH ). C NMR (75 MHz,
CDCl , d):14.0–29.5 (CH ), 31.8 (b-CH ), 35.5 ( ), 81.1 (CH-O), 177.1 (C=O).
ESI-Mass m/z: [m +Na] 207, [m +1+Na] 208. (b) -stearolactone: A mixture of
oleic acid (2 g, 7.8 mmol) and IL (2.9 g, 7.8 mmol) was stirred at 150 °C. After
h, the product was separated from IL by extracting first with a binary mixture
6
the preparation of c-undecalactone under the optimized reaction
1
1
conditions of 0.5:1.0 molar ratio of IL:UDA at 130 °C over a period
of 8 h. In the first reaction conducted with recycled IL, the catalytic
activity of the IL was found to decrease, resulting in the formation
of 55% of c-undecalactone. Earlier work carried out by us using the
same Lewis acidic IL for the liquid–liquid biphasic novel synthesis
c
c
8
c
1
H
of long chain wax esters, the recovered IL was found to be recycla-
1
6
3
a
2
ble at least for 6 successive operations. It is not clear at this stage
the possible reason for loss of activity of the IL observed in the first
recycled reaction for the tandem isomerization–lactonization of
1
(
2
2
2
13
2
2
), 0.85 (t, 3H, CH
-CH
3
3
2
2
a
2
+
+
c
UDA to form
In conclusion, a novel and efficient tandem isomerization–lact-
onization of unsaturated fatty acids to -lactones using the Lewis
acidic IL, choline chlorideÁ2ZnCl as solvent/catalyst is reported.
c-undecalactone.
4
c
of ethyl acetate and hexane (30:70) and finally with hexane. The organic
solvent was evaporated to get 1.73 g of crude product, which was crystallized
1
8
2
from acetone at À20 °C to get 1.48 g of
yield, 74%). The structure of the product was confirmed by H and C NMR,
ESI-Mass and matched well with literature report.4 1H NMR (300 MHz, CDCl
d): 4.46 (tt, 1H, CH–O), 2.51 (dd, 2H, -CH ), 2.31–2.26(m, 1H, b-CH ), 1.90–
), 1.75–1.60 (m, 1H, d-CH ), 1.60–1.50 (m, 1H, d-CH ), 1.40–
). C NMR (75 MHz, CDCl , d):14.0–29.5
-CH ), 81.1 (CH–O), 177.1 (C@O). ESI-Mass m/z:
c-stearolactone as white solid (isolated
The present method shows superior catalytic activity and en-
hanced regiospecificity than other reported hazardous catalytic
systems. Moreover, lactonization of very long chain fatty acids as
well as fatty acids with central double bond (like oleic and erucic
1 13
3
,
a
2
2
1
1
.75 (m, 1H, b-CH
.10 (m, 24H, 12CH
2
2
2
13
2
), 0.85 (t, 3H, CH
3
3
acid) could be achieved at ease and the corresponding
c
-lactones
(CH ), 31.8 (b-CH ), 35.5 (
a
2
2
2
+
+
[
m +Na] 305.3, [m +1+Na] 306.3. (c)
c-erucalactone: A mixture of erucic acid
2 g, 5.9 mmol) and IL (2.42 g, 5.9 mmol) was stirred at 150 °C. After 4 h, the
are obtained in high yields compared to any other reported meth-
ods. However, loss in activity of the recovered IL was observed
which restricts their recyclability.
(
product was separated from IL by extracting first with ethyl acetate and then
with hexane. The organic solvent was evaporated to get 1.86 g of crude
product, which was crystallized from acetone at À20 °C to get 0.8 g of
c-
erucalactone as white solid (isolated yield is 42%). The structure of the product
Acknowledgements
was confirmed by 1H NMR, C NMR and ESI-Mass. 1H NMR (300 MHz, CDCl
d): 4.46 (tt, 1H, CH–O), 2.51 (dd, 2H, -CH ), 2.31–2.26(m, 1H, b-CH ), 1.90–
1.75 (m, 1H, b-CH ), 1.75–1.60 (m, 1H, d-CH ), 1.60–1.50 (m,1H, d-CH ), 1.40–
.10(m, 32H, 16CH ). C NMR (75 MHz, CDCl , d):14.0–29.5
CH ), 31.8 (b-CH ), 35.5 ( ), 81.1 (CH–O), 177.1 (C@O). ESI-Mass m/z:
m +Na] 361.4, [m +1+Na] 362.4.
13
,
3
a
2
2
Financial grant from the New Agricultural Initiative Project
2
2
2
13
1
2
), 0.85 (t, 3H, CH
-CH
+
3
3
(
NAIP), Indian Council of Agricultural Research (ICAR), Govt. of
(
[
2
2
a
2
India is gratefully acknowledged.
+