A synthesis of (S)-(-)-umbelactone and related α,β-butenolides

Article abstract of DOI:10.1055/s-0029-1219181

The development of an asymmetric route for the synthesis of α,β-butenolide building blocks, starting from commercially available D-mannitol, is described. The devised route was applied to a synthesis of the (S)-(-)-enantiomer of the antiviral natural product umbelactone, together with the construction of other synthetically useful lactone structures. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0029-1219181

LETTER
547
A Synthesis of (S)-(–)-Umbelactone and Related a,b-Butenolides
(S
)-(–)-Umbelactone an
i
dRelat
l
ed
a
,
b
-
l
Buteno
i
lides am P. D. Goldring,* John Mann, Paul Brockbank
School of Chemistry and Chemical Engineering, Queen’s University Belfast, David Keir Building, Stranmillis Road, Belfast,
Northern Ireland BT9 5AG, United Kingdom
Fax +44(0)2890976524; E-mail: w.goldring@qub.ac.uk
Received 14 October 2009
We dedicate this Letter to Prof. Gerry Pattenden on the special occasion of his 70th birthday.
O
O
Abstract: The development of an asymmetric route for the synthe-
sis of a,b-butenolide building blocks, starting from commercially
available D-mannitol, is described. The devised route was applied to
a synthesis of the (S)-(–)-enantiomer of the antiviral natural product
umbelactone, together with the construction of other synthetically
useful lactone structures.
O
O
O
H
O
TBSO
PMBO
TBSO
PMBO
OH
HO
R2
R1
umbelactone
(S)-(–)-(1)
2
3
Key words: umbelactone, butenolide, chiral pool, antiviral agents,
lactones
Figure 1 (S)-(–)-Umbelactone (1) and related butenolides
tivity and/or in low yield.6d,8a,9 Accordingly, these results
guided our approach for the selective formation of the cor-
rect alkene geometry required for elaboration of the but-
enolide structure. The ketone 5, and related structures
such as 9, could be derived from D-mannitol (6) via the
corresponding Weinreb amide 89,10 or the aldehyde 19.11
Based on this approach, here we describe a synthetic route
to a,b-butenolide structures, e.g. 2, and report on its appli-
cation in the synthesis of the (S)-(–)-enantiomer of the
natural product umbelactone (1).
Chiral, enantiomerically pure building blocks play an im-
portant role in the synthesis of biologically important
compounds. This includes the butenolides, which appear
in natural products and related structures1 and have been
employed as key intermediates in synthesis.2 A variety of
synthetic approaches towards these structures have been
reported,3 many of which employ sugars or their deriva-
tives as a source of chirality.
The family of natural a,b-butenolide structures includes
umbelactone (1), which was isolated from the Indian plant
Memycelon umbelatum Brum., whose crude extracts ex-
hibit spasmolytic and anti-amphetamine activities, togeth-
er with activity against Ranikhe disease.4 Umbelactone
(1) was first synthesized in racemic form in 19835 and, to-
gether with its S-enantiomer, this natural butenolide has
been the target of various asymmetric synthetic approach-
es.6 Recently, three cinnamate derivatives of 1 were iso-
lated from Crypteronia paniculata that have been shown
to mediate DNA cleavage.7
O
COOEt
O
O
O
2
O
OPMB
OPMB
4
5
Scheme 1 Retrosynthetic analysis of the a,b-butenolide 2
Based on the strategy described above, our synthesis of
butenolides such as 2, began with the construction of D-
glycerate-type subunits. Following the established two-
step protocol, which is based on a ruthenium catalyzed ox-
idative cleavage, the sodium D-glycerate 7 was prepared
from commercially available D-mannitol (6; Scheme 2).12
DCC mediated coupling of the carboxylate 7 with N,O-
dimethylhydroxylamine hydrochloride in the presence of
triethylamine gave the Weinreb amide 8 in 57% yield.6d,9
The amide 8 was then treated with the Grignard reagent
derived from 4-bromobut-1-ene to give the ketone 9 in
82% yield. In a similar manner, the ketones 5 and 10 were
synthesised from 8 using the Grignard reagents derived
from 1-bromo-3-(p-methoxybenzyloxy)propane and 1-
bromo-3-(tert-butyldimethylsiloxy)propane, respectively.
Our attempts to convert the ketone 10 into the correspond-
ing enoate (cf. 4) using methyl (triphenylphosphoranyli-
dene)acetate, led to the desired product as a mixture of
We were interested in employing natural umbelactone (1),
together with related a,b-butenolide structures such as 2,
for the elaboration of highly substituted and stereochemi-
cally complex lactones such as 3 (Figure 1). This led us to
consider a synthetic approach to the butenolide structure
that could be applied to a synthesis of umbelactone (1) and
related structures.
Our strategy for the construction of a,b-butenolide struc-
tures, for use as building blocks in the synthesis of natural
products, demanded the preparation of 2 from the ketone
5 via the (Z)-enoate 4 (Scheme 1).8 However, previous re-
ports have shown that Wittig-type olefination reactions on
related systems, viz. 5→4, proceed with poor stereoselec-
SYNLETT 2010, No. 4, pp 0547–0550
0
1.
0
3.
2
0
1
0
Advanced online publication: 15.01.2010
DOI: 10.1055/s-0029-1219181; Art ID: D29309ST
© Georg Thieme Verlag Stuttgart · New York

548
William P. D. Goldring et al.
LETTER
alkene isomers in poor yield. These conditions were not tone 14 in quantitative yield. Selective protection of the
suitable for elaboration of the butenolide structure. Suc- primary alcohol of the diol 14 was performed using TB-
cessful examples of E-selective Wittig-type olefination SCl and imidazole in DMF to give the silyl ether 16 in
reactions on ketones related to 10 have been reported.13 56% yield. Treatment of the mixture of diastereoisomers
However, in these cases it would not be possible to elabo- of the alcohol 16 with thionyl chloride in pyridine gave
rate the butenolide structure due to the geometry of the the target butenolide 18 in 85% yield.
alkene. We were, however, able to convert the ketone 10
into the alkene 11 in 86% yield using methyltriphe-
O
9
O
nylphosphonium bromide with n-butyllithium in THF.
Unfortunately, our attempts to react the alkene 11 with ei-
ther methyl acrylate or allyl alcohol, under cross-alkene
metathesis conditions, were not successful. The frustra-
tion we encountered in attempting to form the desired (Z)-
enoate, such as 4, led us to consider other options for the
addition of a two-carbon unit into the ketone 9.
O
COOEt
a
b
HO
O
or
HO
HO
5
R
R
12, R = CH=CH2
13, R = CH2OPMB
14, R = CH=CH2
15, R = CH2OPMB
O
O
O
O
c
d
TBSO
TBSO
OH OH
HO
O
ref. 11
R
R
HO
O
OH
O
16, R = CH=CH2
17, R = CH2OPMB
18, R = CH=CH2
2, R = CH2OPMB
OH OH
O–Na+
D-mannitol (6)
7
Scheme 3 Reagents and conditions: (a) ethyl bromoacetate, Zn/Cu,
THF, ultrasonication, 88% (12) or 80% (13); (b) Amberlyst 15, EtOH,
99% (14) or 89% (15); (c) TBSCl, imidazole, DMF, 0 °C to r.t., 56%
(16) or CH2Cl2, 0 °C to r.t., 60% (17); (d) SOCl2, pyridine, 0 °C, 85%
(18) or 80 °C, 25% (2).
O
O
O
b
a
O
O
O
N
R
MeO
Me
The corresponding butenolide 2 was synthesised from the
ketone 5 using the sequence of steps described above. For
example, the b-hydroxy ester 13, which was obtained as
an inseparable 4:1 mixture of diastereoisomers from the
ketone 5 using Reformatsky chemistry, was converted
into the TBS-protected lactone 17 via the dihydroxy lac-
tone 15 (see Scheme 3). Treatment of the mixture of dias-
tereoisomers of the alcohol 17 with thionyl chloride in
pyridine, at 80 °C, gave the target butenolide 2 in 25%
yield, which was not optimised. During the optimisation
of a related system, treatment of the alcohol 16 using the
same reagents at 0 °C gave the butenolide 18 in 85%
yield.
9, R = CH=CH2
8
5, R = CH2OPMB
c
O
O
d
O
O
O
OTBS
OTBS
10
11
Scheme 2 Reagents and conditions: (a) MeO(Me)NH·HCl, DCC,
Et3N, CH2Cl2, 0 °C to r.t., 57%; (b) 4-bromobut-1-ene or 1-bromo-3-
(p-methoxybenzyloxy)propane, Mg, THF, 0 °C to r.t., 82% (9) or
47% (5); (c) 1-bromo-3-(tert-butyldimethylsiloxy)propane, Mg,
THF, 0 °C, 63%; (d) Ph3PCH2Br, n-BuLi, THF, 0 °C, 86%.
We then set out to apply the synthetic route described
above to a synthesis of umbelactone (1). Using a modified
version of the classic Baer two-step protocol, aldehyde 19
was prepared from D-mannitol (6).11 Treatment of 19 with
methylmagnesium bromide, followed by oxidation of the
resulting alcohol with PCC in the presence of sodium ac-
etate and 4 Å molecular sieves, gave the methyl ketone 20
(Scheme 4).15 Using the Reformatsky conditions de-
scribed earlier, the ketone 20 was converted into a 4:1
mixture of diastereoisomers of the b-hydroxy ester 21 in
86% combined yield. The mixture of diastereoisomers
was carried through the following two steps without any
observed change to the diastereoisomeric ratio. Lactone
22 was obtained from the alcohol 21 in 56% yield over
two steps, based on a deprotection–lactonisation sequence
using Amberlyst 15, followed by selective protection of
the resulting primary alcohol as the silyl ether. Treatment
of the diastereoisomeric mixture of the alcohol 22 with
thionyl chloride in pyridine gave the butenolide 23 in 57%
An appealing solution to this synthetic problem that
avoids the formation of the unwanted alkene isomer or
isomer mixtures, involves a two-carbon addition to the
ketone 9 using Reformatsky chemistry.14 Although this
method leads to the formation of diastereoisomers, the
new stereogenic centre is removed at a later stage in the
synthesis and, therefore, all of the material is converted
into the target butenolide. For example, the ketone 9 was
treated with ethyl bromoacetate in the presence of a zinc-
copper couple, in an ultrasonic bath, to give an insepara-
ble 4:1 mixture of diastereoisomers of the b-hydroxy ester
12 in 88% combined yield (Scheme 3). The mixture of
diastereoisomers was carried through the following two
steps, i.e. 12→14→16, without any observed change to
the diastereoisomeric ratio. Treatment of the alcohol 12
with Amberlyst 15 in ethanol unmasked the diol, which
then suffered spontaneous lactonisation to give the lac-
Synlett 2010, No. 4, 547–550 © Thieme Stuttgart · New York

LETTER
(S)-(–)-Umbelactone and Related a,b-Butenolides
549
yield. Finally, deprotection of the silyl ether 23 using bo- Supporting Information for this article is available online at
ron trifluoride diethyl etherate gave (S)-(–)-umbelactone http://www.thieme-connect.com/ejournals/toc/synlett.
(1) in 43% yield. The NMR data recorded for synthetic
(S)-(–)-1, together with the specific rotation, were identi-
Acknowledgment
cal to the data reported in the literature.6,16
We thank Queen’s University Belfast and the Department for Em-
ployment and Learning (studentship to P.B.) for their support of this
work.
O
ref. 10
a,b
d,e
O
6
O
O
O
CHO
References and Notes
19
20
(1) For recent examples, see: (a) Rigano, D.; Grassia, A.;
Bruno, M.; Rosselli, S.; Piozzi, F.; Formisano, C.; Arnold,
N. A.; Senatore, F. J. Nat. Prod. 2006, 69, 836.
O
O
O
COOEt
c
TBSO
O
(b) Sobolev, V. S.; Deyrup, S. T.; Gloer, J. B. J. Agric. Food
Chem. 2006, 54, 2111. (c) Jones, W. P.; Lobo-Echeverri, T.;
Mi, Q.; Chai, H.-B.; Soejarto, D. D.; Cordell, G. A.;
Swanson, S. M.; Kinghorn, A. D. J. Nat. Prod. 2007, 70,
372. (d) Ueoka, R.; Nakao, Y.; Fujii, S.; van Soest, R. W.
M.; Matsunaga, S. J. Nat. Prod. 2008, 71, 1089.
(2) For recent applications of butenolides in synthesis, see:
(a) Doroh, B.; Sulikowski, G. A. Org. Lett. 2006, 8, 903.
(b) Tang, B.; Bray, C. D.; Pattenden, G. Tetrahedron Lett.
2006, 47, 6401. (c) Li, Y.; Nawrat, C. C.; Pattenden, G.;
Winne, J. M. Org. Biomol. Chem. 2009, 7, 639.
(d) Weinreb, S. M. Nat. Prod. Rep. 2009, 26, 758.
(3) For reviews on the synthesis of butenolides, see: (a) Rao,
Y. S. Chem. Rev. 1976, 76, 625. (b) Carter, N. B.; Nadany,
A. E.; Sweeney, J. B. J. Chem. Soc., Perkin Trans. 1 2002,
2324.
HO
HO
22
21
23
O
O
O
O
f
g
TBSO
HO
(S)-(–)-1
Scheme 4 Reagents and conditions: (a) MeMgBr, THF, 0 °C to r.t.,
52%; (b) PCC, NaOAc, 4Å MS, CH2Cl2, 0 °C to r.t., 74%; (c) ethyl
bromoacetate, Zn/Cu, THF, ultrasonication, 86%; (d) Amberlyst 15,
EtOH, 99%; (e) TBSCl, DMAP, Et3N, CH2Cl2, 0 °C to r.t., 56%; (f)
SOCl2, pyridine, 0 °C, 57%; (g) BF3·OEt2, CHCl3, r.t., 43%.
(4) Agarwal, S. K.; Rastogi, R. P. Phytochemistry 1978, 17,
1663.
In conclusion, a synthetic route was developed for the
construction of the a,b-butenolide structures 2 and 18
from D-mannitol via glyceraldehyde-type derivatives
such as 8 or 19. Our approach employed Reformatsky
chemistry for the construction of the carbon framework,
for example 9→12. The deprotection–lactonisation of
products such as 12, prior to the formation of the alkene
unit, enabled us to convert the mixture of diastereoiso-
mers resulting from the Reformatsky step into the target
butenolides. Furthermore, our route avoided the use of un-
productive and non-selective Wittig-type protocols for the
conversion of the intermediate ketones 9 or 5 into the cor-
responding alkene, such as 4.6d,8a,9 The synthetic route de-
scribed for the construction of the butenolides 2 and 18
was successfully applied to a synthesis of (S)-(–)-um-
belactone (1). We plan to employ the butenolide 2 as a key
building block in our synthetic approach to the anti-malar-
ial natural product anthecularin (24),17 via the diene-yne
lactone 25 (Scheme 5). Anthecularin (24) was recently
synthesized for the first time by Pattenden and co-work-
ers.2c The progress of this research, together with a full ac-
count of our synthetic studies towards the butenolide
structure will be described in due course.
(5) (a) Caine, D.; Frobese, A. S.; Ukachukwu, V. C. J. Org.
Chem. 1983, 48, 740. (b) For a later racemic synthesis of 1,
see: Bonete, P.; Nájera, C. J. Org. Chem. 1994, 59, 3202.
(6) For syntheses of (+)-1 and/or (–)-1, see: (a) Ortuño, R. M.;
Bigorra, J.; Font, J. Tetrahedron 1987, 43, 2199. (b) Sato,
T.; Okumura, Y.; Itai, J.; Fujisawa, T. Chem. Lett. 1988,
1537. (c) Boeckman, R. K.; Charette, A. B.; Asberom, T.;
Johnston, B. H. J. Am. Chem. Soc. 1991, 113, 5337.
(d) Gibson, C. L.; Handa, S. Tetrahedron: Asymmetry 1996,
7, 1281. (e) Ha, H.-J.; Yoon, K.-N.; Lee, S.-Y.; Park, Y.-S.;
Lim, M.-S.; Yim, Y.-G. J. Org. Chem. 1998, 63, 8062.
(f) Liu, H. W.; Li, Y. L. Chin. Chem. Lett. 2005, 16, 716.
(g) Liu, H.; Zhang, T.; Li, Y. Chirality 2006, 18, 223.
(h) Kamal, A.; Krishnaji, T.; Reddy, P. V. Tetrahedron Lett.
2007, 48, 7232.
(7) Deng, J.-Z.; Newman, D. J.; Hecht, S. M. J. Nat. Prod. 2005,
68, 465.
(8) For recent, or related, syntheses of the butenolide structure,
see: (a) Mulzer, J.; Pietschmann, C.; Schöllhorn, B.;
Buschmann, J.; Luger, P. Liebigs Ann. 1995, 1433.
(b) Linclau, B.; Boydell, A. J.; Clarke, P. J.; Horan, R.;
Jacquet, C. J. Org. Chem. 2003, 68, 1821. (c) Geraghty,
N. W. A.; Hernon, E. M. Tetrahedron Lett. 2009, 50, 570.
(9) Kabeya, M.; Hamada, Y.; Shioiri, T. Tetrahedron 1997, 53,
9769.
(10) For a related preparation of 8, see: White, J. D.; Quaranta, L.;
Wang, G. J. Org. Chem. 2007, 72, 1717.
OPMB
(11) (a) Baer, E.; Fischer, H. O. L. J. Biol. Chem. 1939, 128, 463.
(b) LeCocq, J.; Ballou, C. E. Biochemistry 1964, 3, 976.
(c) For a review, see: Jurczak, J.; Pikul, S.; Bauer, T.
Tetrahedron 1986, 42, 447. (d) For other recent methods
for the preparation of the aldehyde 19, see: Zhong, Y.-L.;
Shing, T. K. M. J. Org. Chem. 1997, 62, 2622. (e) Palomo,
C.; Oiarbide, M.; Landa, A.; Esnal, A.; Linden, A. J. Org.
Chem. 2001, 66, 4180.
O
H
2
OTBS
O
HO
O
O
O
anthecularin (24)
25
Scheme 5 Retrosynthetic analysis of anthecularin (24)
Synlett 2010, No. 4, 547–550 © Thieme Stuttgart · New York

550
William P. D. Goldring et al.
LETTER
(12) (a) Emons, C. H. H.; Kuster, B. F. M.; Vekemans, J. A. J. M.;
Sheldon, R. A. Tetrahedron: Asymmetry 1991, 2, 359.
(b) For related procedures, see: Ruholl, H.; Schäfer, H. J.
Synthesis 1988, 54. (c) Earle, M. J.; Abdur-Rashid, A.;
Priestley, N. D. J. Org. Chem. 1996, 61, 5697.
(13) (a) Tanner, D.; Somfai, P. Tetrahedron 1987, 43, 4395.
(b) Toyama, K.; Iguchi, S.; Sakazaki, H.; Oishi, T.; Hirama,
M. Bull. Chem. Soc. Jpn. 2001, 74, 997.
1-[(R)-2,2-Dimethyl-1,3-dioxolan-4-yl]pent-4-en-1-one
(9). [a]D20 +14.9 (c 1.0 in CHCl3); IR(film): 3079, 2988,
2934, 1716, 1641, 1373, 1217, 1068 cm–1; 1H NMR (300
MHz, CDCl3): d = 5.82 (ddt, J = 16.8, 10.4, 6.4 Hz, 1 H,
H2C=CH), 5.08–4.95 (m, 2 H, C=CH2), 4.43 (dd, J = 5.5, 2.3
Hz, 1 H, OCHH), 4.19 (t, J = 7.7 Hz, 1 H, CH), 3.98 (dd,
J = 5.5, 2.3 Hz, 1 H, OCHH), 2.74–2.68 (m, 2 H, COCH2),
2.37–2.29 (m, 2 H, H2C=CHCH2), 1.48 (s, 3 H, CH3), 1.39
(s, 3 H, CH3); 13C NMR (75 MHz, CDCl3): d = 210.1, 136.9,
115.3, 110.9, 80.2, 66.5, 37.7, 26.9, 26.0, 25.0.
(14) For a similar strategy, see: Tomioka, K.; Tanaka, M.; Koga,
K. Chem. Pharm. Bull. 1989, 37, 1201.
(15) (a) Jacobi, P. A.; Kaczmarek, C. S. R.; Udodong, U. E.
Tetrahedron 1987, 43, 5475. (b) Munier, P.; Krusinski, A.;
Picq, D.; Anker, D. Tetrahedron 1995, 51, 1229. (c) Kis,
K.; Wungsintaweekul, J.; Eisenreich, W.; Zenk, M. H.;
Bacher, A. J. Org. Chem. 2000, 65, 587. (d) Scholte, A. A.;
Vederas, J. C. Org. Biomol. Chem. 2006, 4, 730.
4-(tert-Butyldimethylsilanyloxy)-1-[(R)-2,2-dimethyl-
1,3-dioxolan-4-yl]butan-1-one (10). [a]D20 –0.4 (c 1.1 in
CHCl3); IR(film): 2932, 2859, 1718, 1255, 1101 cm–1; 1H
NMR (300 MHz, CDCl3): d = 4.44 (dd, J = 7.7, 5.6 Hz, 1 H,
OCHH), 4.19 (dd, J = 8.7, 7.7 Hz, 1 H, CH), 3.98 (dd,
J = 8.7, 5.7 Hz, 1 H, OCHH), 3.62 (t, J = 6.0 Hz, 2 H,
TBSOCH2), 2.69 (t, J = 7.0 Hz, 2 H, COCH2), 1.83–1.74 (m,
2 H, TBSOCH2CH2), 1.48 (s, 3 H, CH3), 1.39 (s, 3 H, CH3),
0.88 (s, 9 H, Si(CH3)3), 0.03 (s, 6 H, Si(CH3)2); 13C NMR (75
MHz, CDCl3): d = 210.8, 110.9, 80.3, 66.5, 62.0, 35.0, 26.0,
25.9, 25.0, 18.3, –5.4; HRMS (ES): m/z [M + Na]+ calcd for
C15H30O4SiNa: 325.1811; found: 325.1834 (20%).
tert-Butyl-{4-[(S)-2,2-dimethyl-1,3-dioxolan-4-yl]pent-4-
enyloxy}dimethylsilane (11). [a]D20 +6.0 (c 0.9 in CHCl3);
IR(film): 2928, 2857, 1650, 1471, 1379, 1256, 1214 cm–1;
1H NMR (300 MHz, CDCl3): d = 5.15 (br s, 1 H, C=CHH),
4.90 (t, J = 0.7 Hz, 1 H, C=CHH), 4.53 (t, J = 7.5 Hz, 1 H,
OCHH), 4.11 (dd, J = 8.0, 6.5 Hz, 1 H, CH), 3.65–3.58 (m,
3 H, OCHH and TBSOCH2), 2.13–1.97 (m, 2 H, H2C=CCH2),
1.74–1.64 (m, 2 H, TBSOCH2CH2), 1.44 (m, 3 H, CH3),
1.40 (s, 3 H, CH3), 0.89 (s, 9 H, Si(CH3)3), 0.04 (s, 6 H,
Si(CH3)2); 13C NMR (75 MHz, CDCl3): d = 146.7, 111.1,
109.6, 79.4, 69.4, 63.1, 31.5, 28.1, 26.8, 26.3, 26.1, 18.7,
–4.9.
(16) Full experimental details for the compounds 2, 18, 23 and
(S)-(–)-1, including proton and carbon NMR spectra, are
available in the Supporting Information. The following
spectroscopic data were recorded for key intermediates.
1-[(R)-2,2-Dimethyl-1,3-dioxolan-4-yl]-4-(4-methoxy-
benzyloxy)butan-1-one (5). [a]D20 +1.6 (c 1.2 in CHCl3);
IR(film): 2988, 2935, 2860, 1716, 1612, 1513, 1456, 1373,
1302, 1210 cm–1; 1H NMR (300 MHz, CDCl3): d = 7.25–
7.22 (m, 2 H, ArH), 6.89–6.83 (m, 2 H, ArH), 4.40 (s, 2 H,
OCH2PMP), 4.23 (dd, J = 7.7, 5.7 Hz, 1 H, OCHHCH), 4.17
(dd, J = 8.7, 8.0 Hz, 1 H, CH), 3.95 (dd, J = 8.7, 5.7 Hz, 1 H,
OCHHCH), 3.80 (s, 3 H, OCH3), 3.45 (t, J = 6.2 Hz, 2 H,
PMBOCH2), 2.70 (t, J = 7.2 Hz, 2 H, COCH2), 1.92–1.83
(m, 2 H, PMBOCH2CH2), 1.47 (d, J = 0.6 Hz, 3 H, CH3),
1.38 (d, J = 0.6 Hz, 3 H, CH3); 13C NMR (75 MHz, CDCl3):
d = 210.4, 159.1, 130.4, 129.2, 113.7, 110.8, 80.2, 72.5, 68.8,
66.5, 55.2, 35.4, 26.0, 25.0, 23.1; HRMS (EI): m/z [M]+
calcd for C17H24O5: 308.1624; found: 308.1647 (5%).
(17) Karioti, A.; Skaltsa, H.; Linden, A.; Perozzo, R.; Brun, R.;
Tasdemir, D. J. Org. Chem. 2007, 72, 8103.
Synlett 2010, No. 4, 547–550 © Thieme Stuttgart · New York