Enantioselective total synthesis of polyoxygenated cyclohexanoids: (+)-streptol, ent-RKTS-33 and putative '(+)-parasitenone'. Identity of parasitenone with (+)-epoxydon

Article abstract of DOI:10.1016/j.tetlet.2005.03.087

Short, simple and enantioselective syntheses of the natural product (+)-streptol, the non-peptide apoptosis inhibitor ent-RKTS-33 and the putative structure of 'parasitenone' have been accomplished from the readily available chiral building block. 'Parasi

Full text of DOI:10.1016/j.tetlet.2005.03.087

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 3373–3376
Enantioselective total synthesis of polyoxygenated
cyclohexanoids: (+)-streptol, ent-RKTS-33 and putative
ꢀ(+)-parasitenoneꢁ.Identity of parasitenone with (+)-epoxydon
Goverdhan Mehta,* Shashikant R. Pujar, Senaiar S. Ramesh and Kabirul Islam
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
Received 14 January2005; revised 8 March 2005; accepted 15 March 2005
Available online 2 April 2005
Abstract—Short, simple and enantioselective syntheses of the natural product (+)-streptol, the non-peptide apoptosis inhibitor
ent-RKTS-33 and the putative structure of ꢀparasitenoneꢁ have been accomplished from the readilyavailable chiral building block.
ꢀParasitenoneꢁ has been shown to be identical with the known natural product epoxydon.
Ó 2005 Elsevier Ltd. All rights reserved.
Polyketide natural products, based on the epoxyquinone
motif 1, and exhibiting a wide-ranging biological profile
ranging from phytotoxic, anti-fungal, anti-bacterial,
anti-tumour and enzyme inhibitory activity, have
manyinnovative strategies have been devised towards
their synthesis.2 Our group has also been drawn to this
arena and we have delineated a simple, general ap-
proach to this class of natural products from the readily
available Diels–Alder adduct 7 of cyclopentadiene and
p-benzoquinone (Scheme 1).3 Recently, an enantioselec-
tive version, based on a kinetic enzymatic resolution of
intermediate 8, has also been developed and provided
a convenient access to the enantiomericallyenriched
building blocks (+)-9 and (ꢀ)-8 (Scheme 1).3g
1
surfaced regularlyfrom diverse natural sources. The
variegated substitution and polyoxygenation pattern
displayed by these natural products is amply demon-
strated in cyclohexanoid natural products like (ꢀ)-phyl-
lostine 2,1a (+)-epoxydon 3a,1b (+)-epiepoxydon 3b,1c
(+)-harveynone 4,1d (ꢀ)-cycloepoxydon 51e and (+)-am-
buic acid 61f to name a few. These and related polyoxy-
genated cyclohexanoid natural products have attracted
synthetic interest from several research groups and
In this letter, we describe the elaboration of the chiral
precursor (+)-9 to the natural product (+)-streptol 10,
OTBS
O
O
OH
H
ref. 3g
O
O
O
O
O
O
H
C
O
R
OH
O
OH
O
HO
7
8
1 R= OH, =O
3a β-OH, (+)-Epoxydon
3b α-OH, (+)-Epiepoxydon
2 (-)-Phyllostine
a
OH
O
O
HO
OH
OTBS
O
O
OTBS
OAc
O
C5H11
O
CO2H
+
O
OH OH
O
O
O
(+)-9
O
4 (+)-Harveynone 5 (-)-Cycloepoxydone 6 (+)-Ambuic acid
HO
(-)-8
*
Scheme 1. Reagents and conditions: (a) Lipase PS-D (Amano), vinyl
acetate, rt, 28 h, (+)-9, 46%, ꢁ99% ee, (ꢀ)-8, 45%, ꢁ99% ee.
Corresponding author. Tel.: +91 80 22932850; fax: +91 80
23600936; e-mail: gm@orgchem.iisc.ernet.in
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.03.087

3374
G. Mehta et al. / Tetrahedron Letters 46 (2005) 3373–3376
ent-RKTS-33 11 and the putative structure of the re-
centlyisolated natural product ꢀ(+)-parasitenoneꢁ 12.
At this juncture, we were drawn to the literature reports
dealing with two epimeric polyoxygenated epoxyqui-
noids. The first one, byKakeya et al. in 2003, described
RKTS-33 ent-11 as a novel non-peptide inhibitor of
death-receptor mediated apoptosis.9 The other report
in 2002 bySon et al., recorded the isolation of a new
natural product, parasitenone (+)-12 from the marine
algicolous fungus Apergillus parasiticus with promising
free radical scavenging activity.10 Interestingly, the two
compounds RKTS-33 ent-11 and (+)-parasitenone 12
were found to be epimeric at C4, belonged to opposite
enantiomeric series and exhibited verydifferent biologi-
cal activity. Our chiral building block (+)-9 appeared
to be well poised for elaboration to RKTS-33 11 and
(+)-12.
O
O
OH
OH
OH
1
4
2
O
O
OH OH
11 ent-RKTS-33
OH OH
OH OH
10 (+)-Streptol
12 "(+)-Parasitenone"
(+)-Streptol 10 (also known as valienol) was isolated
from a culture of an unidentified Streptomyces sp. by
Sakuda et al. and shown to inhibit the growth of lettuce
seedlings at a concentration above 13 ppm.4 To date,
two syntheses of racemic 10 bySuami et al. 5a and Block
Retro-Diels–Alder reaction of the enantiomericallypure
tricyclic acetate (+)-9 furnished epoxycyclohexenone
(+)-18,7 and further 1,2-reduction gave a diastereomeric
mixture of alcohols 19a,b (a:b = 1:2), in which the b-iso-
mer was the major product (Scheme 3). The epimeric
alcohols 19a,b were converted to their TBS ether deriva-
tives (+)-20/(+)-21, respectively, and readily separated
et al.5b and of ent-10 byMu ller et al.5c have been re-
¨
ported. Our synthetic approach to the natural enantio-
mer (+)-10 emanated from the chiral tricyclic acetate
(+)-9, which was subjected to BF3ÆEt2O mediated and
acetate-assisted regioselective cleavage of the epoxide
ring to furnish the trans-diol (ꢀ)-13 (Scheme 2).6,7
The trans-diol moietyin ( ꢀ)-13 was protected as the diace-
tate, (+)-14. Thermal activation of the tricyclic adduct
(+)-14 induced a facile retro-Diels–Alder reaction, with
the elimination of cyclopentadiene, to deliver the enone
(+)-15. Reduction of the carbonyl functionality in (+)-15
under Luche conditions8 was stereoselective and fur-
nished the endo-alcohol (+)-16.7 TBS deprotection in
7
bycolumn chromatography. The acetate in the a-iso-
mer (+)-20 was removed to give alcohol (ꢀ)-22, which
was subsequentlyoxidized to the enone ( ꢀ)-23 (Scheme
25
4).7 Finally, TBS deprotection in (ꢀ)-23 furnished
RKTS-33 (ꢀ)-11 ½aꢂ ꢀ275.7 (c 0.33, C2H5OH), whose
7,9
reported byKakeya et al.
D
spectral data were in complete agreement with those
(+)-16 gave (+)-17 and acetate hydrolysis furnished
In another sequence, the major b-isomer (+)-21 was sub-
jected to acetate hydrolysis to give alcohol (ꢀ)-24
(Scheme 5).7 MnO2 mediated allylic oxidation of (ꢀ)-
24 led to the enone (ꢀ)-25, which on TBS deprotection
furnished the enone diol (ꢀ)-12 corresponding to the
structure assigned to the natural product ꢀparasit-
enoneꢁ.10 However, the spectral data of our synthetic
sample and those reported bySon et al. were a complete
mismatch.11 To confirm further, the stereochemical
25
D
the natural product, streptol (+)-10 ½aꢂ +91.8 (c, 0.25,
25
D
H2O); lit.5c synthetic ent-10 ½aꢂ ꢀ92.5 (c 0.2, H2O).
The spectral data of our synthetic compound were
found to be identical in all respects with those reported
for the natural product.4,7
integrityof our synthetic sample, tricyclic exo-alcohol
( )-26, prepared byus in a different context from the
OTBS
OAc
OTBS
O
OTBS
OAc
a
O
OR
OR
(-)-13 R = H
O
O
O
O
O
OAc
OAc
OH
BF3
(+)-9
a
b
b
d
(+)-9
O
O
(+)-14 R = Ac
TBSO
O
TBSO
c
19 α:β=1:2
(+)-18
OH
OAc
OH
OAc
OAc
c
OH
OH
OAc
OAc
f
OAc
O
OAc
OAc
O
+
HO
OH
RO
TBSO
O
(+)-15
(+)-16 R = TBS
(+)-17 R = H
(+)-10 Streptol
e
TBSO
OTBS
(+)-21
TBSO
OTBS
(+)-20
(2:1)
Scheme 2. Reagents and conditions: (a) BF3ÆEt2O, toluene, 0 °C, 1 h,
62%; (b) Ac2O, pyridine, CH2Cl2, 2 h, quant.; (c) Ph2O, 230 °C,
15 min, 91%; (d) NaBH4, CeCl3Æ7H2O, MeOH, 0 °C, 80%; (e) 40% HF,
pyridine, THF, 0 °C, 83%; (f) NaOMe, MeOH, 96%.
Scheme 3. Reagents and conditions: (a) Ph2O, 230 °C, 10 min, 93%;
(b) NaBH4, MeOH, ꢀ50 °C, 5 min, 87%; (c) TBSOTf, 2,6-lutidine,
CH2Cl2, ꢀ10 °C, 83%.

G. Mehta et al. / Tetrahedron Letters 46 (2005) 3373–3376
3375
In short, we have utilized the readilyavailable chiral
OAc
OH
building block (+)-9 for the first synthesis of the natu-
rallyoccurring enantiomer of streptol (+)- 10 and
RKTS-33 (ꢀ)-11. A synthesis of the putative structure
12 assigned to the natural product ꢀparasitenoneꢁ has
shown that its formulation is incorrect. The identityof
the natural product ꢀparasitenoneꢁ with the known com-
pound (+)-epoxydon 3a has been firmlyestablished.
a
O
O
TBSO
OTBS
(+)-20
TBSO
OTBS
(-)-22
b
O
O
c
Acknowledgements
O
O
The work was financiallysupported bythe Chemical and
Biologyunit of JNCASR, Bangalore, India. S.R.P.
thanks IISc while S.S.R. and K.I. thank CSIR, India
for research fellowships. The lipase used in this study
was a gift from Mr. A. Hirano and Mr. T. Nakagawa
Amano Pharmaceutical Co. Ltd. Japan. We would like
to thank Professor B. W. Son for helpful exchange of
information. The single crystal X-ray data were collected
at the CCD facilityof IISc.
HO
OH
TBSO
OTBS
(-)-11 RKTS-33
(-)-23
Scheme 4. Reagents and conditions: (a) LiOH, MeOH, 0 °C, 30 min,
70%; (b) MnO2, CH2Cl2, rt, 6 h, 83%; (c) 40% HF, CH3CN, 0 °C to rt,
3 h, 80%.
OAc
OH
O
a
b
O
O
O
References and notes
TBSO
OTBS
(+)-21
TBSO
OTBS
(-)-24
TBSO
OTBS
(-)-25
1. (a) (ꢀ)-Phyllostine: Sakamura, S.; Ito, J.; Sakai, R. Agric.
Biol. Chem. 1970, 34, 153; Sakamura, S.; Ito, J.; Sakai, R.
Agric. Biol. Chem. 1971, 35, 105; Kerr, K. A. Acta
Crystallogr. 1986, C42, 887; (b) (+)-Epoxydon: Close, A.;
Mauli, R.; Sigg, H. P. Helv. Chim. Acta 1966, 49, 204;
Sakamura, S.; Niki, H.; Obata, Y.; Sakai, R.; Matsumoto,
T. Agric. Biol. Chem. 1969, 33, 698; (c) (+)-Epiepoxydon:
Nagasawa, H.; Suzuki, A.; Tamura, S. Agric. Biol. Chem.
1978, 42, 1303; Sekiguchi, J.; Gaucher, G. M. Biochem. J.
1979, 182, 445; (d) (+)-Harveynone: Nagata, T.; Hirrota,
A. Biosci. Biotechnol. Biochem. 1992, 56, 810; (e) (ꢀ)-
Cycloepoxydon: Gehrt, A.; Erkel, G.; Anke, H.; Anke, T.;
Sterner, O. Nat. Prod. Lett. 1997, 9, 259; Gehrt, A.; Erkel,
G.; Anke, T.; Sterner, O. J. Antibiot. 1998, 51, 455; (f) (+)-
Ambuic acid: Li, J. Y.; Harper, J. K.; Grant, D. M.;
Tombe, B. O.; Bashyal, B.; Hess, W. M.; Strobel, G. A.
Phytochemistry 2001, 56, 463.
c
O
OH
O
OH
O
e
d
O
O
O
O
HO
26
HO
OH
(-)-12
27
Scheme 5. Reagents and conditions: (a) LiOH, MeOH, 0 °C, 30 min,
68%; (b) MnO2, CH2Cl2, rt, 6 h, 86%; (c) 40% HF, CH3CN, 0 °C to rt,
3 h, 80%; (d) DIBAL-H, THF, ꢀ78 °C, 65%; (e) Ph2O, 240 °C, 45 min,
quant.
2. For a review see: Marco-Contelles, J.; Molina, M. T.;
Anjum, S. Chem. Rev. 2004, 104, 2857; (a) Some selected
references: Kamikubo, T.; Ogaswara, K. Chem. Commun.
1996, 1679; (b) Kamikubo, T.; Hiroya, K.; Ogaswara, K.
Tetrahedron Lett. 1996, 37, 499; (c) Taylor, R. J. K.;
Alkaraz, L.; Kapfer-Eyer, I.; Macdonald, G.; Wei, X.;
Lewis, N. Synthesis 1998, 775; (d) Li, C.; Lobskovsky, E.;
Porco, J. A. Jr. J. Am. Chem. Soc. 2000, 122, 10484; (e)
Wood, J. L.; Thompson, B. D.; Yusuff, N.; Pflum, D. A.;
Matthaus, S. P. J. Am. Chem. Soc. 2001, 123, 2097; (f)
Genski, T.; Taylor, R. J. K. Tetrahedron Lett. 2002, 43,
3573; (g) Lei, X.; Johnson, R. P.; Porco, J. A., Jr. Angew.
Chem., Int. Ed. 2003, 42, 3913.
3. (a) Mehta, G.; Islam, K. Tetrahedron Lett. 2003, 44, 3569;
(b) Mehta, G.; Islam, K. Org. Lett. 2004, 6, 807; (c)
Mehta, G.; Pan, S. C. Org. Lett. 2004, 6, 811; (d) Mehta,
G.; Ramesh, S. S. Tetrahedron Lett. 2004, 45, 1985; (e)
Mehta, G.; Islam, K. Tetrahedron Lett. 2004, 45, 3611; (f)
Mehta, G.; Roy, S. Org. Lett. 2004, 6, 2389; (g) Mehta, G.;
Islam, K. Tetrahedron Lett. 2004, 45, 7683; (h) Mehta, G.;
Pan, S. C. Org. Lett. 2004, 6, 3985; (i) Mehta, G.; Pan, S.
C. Tetrahedron Lett. 2005, 46, 3045–3048.
tricyclic diketone 27, was subjected to thermal activation
to furnish ( )-12, spectroscopicallyidentical with ( ꢀ)-12
described above (Scheme 5). Since, the stereostructure of
26 was secured through single crystal X-ray structure
analysis,12 it reconfirmed the stereostructure of our
synthetic 12. These results clearlyindicated that the
assigned structure of the natural product ꢀparasitenoneꢁ
was untenable.10
Consequently, the question arose as to what is ꢀparasit-
enoneꢁ? A critical examination of the spectral data re-
ported for ꢀparasitenoneꢁ bySon et al. with other
similar epoxyquinone based natural product siblings
led us to surmise that ꢀparasitenoneꢁ is in fact identical
with (+)-epoxydon 3a.1b This was confirmed through a
direct spectral (1H and 13C NMR) comparison between
(+)-epoxydon 3a (synthesized earlier by us)3g and ꢀpara-
sitenoneꢁ in DMSO-d6.11 The perfect spectral match
between the two led to the inevitable conclusion that
the recentlyisolated natural product from Apergillus
parasiticus10 is epoxydon 3a and not ꢀparasitenoneꢁ 12.
4. Isogai, A.; Sakuda, S.; Nakayama, J.; Watanabe, S.;
Suzuki, A. Agri. Biol. Chem. 1987, 51, 2277.

3376
G. Mehta et al. / Tetrahedron Letters 46 (2005) 3373–3376
5. (a) Toyokuni, T.; Abe, Y.; Ogawa, S.; Suami, T. Bull.
(dd, J = 3.6, 1.5 Hz, 1H), 3.36–3.34 (m, 1H); 13C NMR
(75 MHz, CD3COCD3) d 194.0, 161.2, 120.1, 63.6, 62.6,
57.7, 53.5; HRMS (ES) m/z calcd for C7H8O4Na
Chem. Soc. Jpn. 1983, 56, 505; (b) Block, O. Dissertation,
Universityof Wuppertal, Germany, 2000; (c) Franke, D.;
Lorbach, V.; Esser, S.; Dose, C.; Sprenger, G. A.; Halfar,
M.; Tho¨mmes, J.; Muller, R.; Takor, R.; Muller, M.
25
[M+Na]+: 179.0320, found 179.0301; (ꢀ)-12 ½aꢂD ꢀ115.4
(c 0.39, C2H5OH); 1H NMR (300 MHz, DMSO-d6) d 5.82
(dd as t, J = 1.8 Hz, 1H), 4.64 (br s, 1H), 4.21 (1/2ABq,
J = 18.3 Hz, 1H), 4.09 (1/2ABq, J = 18.3 Hz, 1H), 3.75
(dd, J = 4.4, 2.9 Hz, 1H), 3.38 (dd, J = 4.2, 2.4 Hz, 1H),
13C NMR (75 MHz, DMSO-d6) d 193.6, 163.0, 117.2,
64.6, 60.4, 55.3, 53.2; HRMS (ES) m/z calcd for
C7H8O4Na [M+Na]+: 179.0320, found 179.0311.
8. Gemal, A. L.; Luche, J. L. J. Am. Chem. Soc. 1981, 103,
5454.
¨
¨
Chem. Eur. J. 2003, 9, 4188.
6. (a) Prystas, M.; Gustafsson, H.; Sorm, F. Collect. Czech.
Chem. Commun. 1971, 36, 1487; (b) Honzumi, M.; Hiroya,
K.; Taniguchi, T.; Ogasawara, K. Chem. Commun. 1999,
1985.
7. All new compounds were fullycharacterized on the basis of
IR, 1H NMR, 13C NMR, and mass data. Spectral data of
25
selected compounds: (ꢀ)-13 ½aꢂD ꢀ3.4 (c 2.34, CHCl3);
IR (neat) 3466, 1742, 1713 cmꢀ1
;
1H NMR (300 MHz,
9. Kakeya, H.; Miyake, Y.; Shoji, M.; Kishida, S.; Hayashi,
Y.; Kataoka, T.; Osada, H. Bioorg. Med. Chem. Lett.
2003, 13, 3743.
CDCl3) d 6.27 (dd, J = 5.1, 2.4 Hz, 1H), 5.97 (dd, J = 5.1,
3.0 Hz, 1H), 5.77 (dd, J = 9.6, 3.9 Hz, 1H), 4.28 (d,
J = 9 Hz, 1H), 4.05 (dd, J = 11.9, 3.8 Hz, 1H), 3.81 (d,
J = 12 Hz, 1H), 3.40 (br s, 1H), 3.33 (d, J = 9.3 Hz, 1H),
3.00 (s, 1H), 2.92 (dd, J = 9.5, 3 Hz, 1H), 2.79 (s, 1H), 2.17
(s, CH3), 1.52 (1/2 ABq, J = 8.7 Hz, 1H), 1.44 (1/2 ABq,
J = 8.7 Hz, 1H), 0.85 (s, 9H), 0.03 (s, 3H), ꢀ0.01 (s, 3H);
13C NMR (75 MHz, CDCl3) d 214.0, 170.6, 139.7, 133.2,
74.9, 72.2, 69.3, 69.2, 62.3, 50.5, 48.3, 46.6, 46.5, 25.8, 21.2,
18.2, ꢀ5.6, ꢀ5.7; HRMS (ES) m/z calcd for C20H32O6Si-
10. Son, B. W.; Choi, J. S.; Kim, J. C.; Nam, K. W.; Kim,
D.-S.; Chung, H. Y.; Kang, J. S.; Choi, H. D. J. Nat. Prod.
2002, 65, 794.
11. Comparison of the spectral data (13C NMR in DMSO-d6)
of natural ꢀparasitenoneꢁ, 10 synthetic 12 and (+)-epoxydon
3a.
193.9, 141.4, 133.8, 63.7, 57.3, 54.0, 52.9
193.6, 163.0, 117.2, 64.6, 60.4, 55.3, 53.2
194.0, 141.4, 133.8, 63.7, 57.6, 54.0, 52.9
25
‘parasitenone’
Synthetic 12
Epoxydon 3a
Na [M+Na]+: 419.1866, found 419.1865; (+)-18 ½aꢂD
(+)-173 (c 1.34, CHCl3); IR (neat) 1743, 1685 cmꢀ1.1H NMR
(300 MHz, CDCl3) d 6.61–6.58 (m, 1H), 5.83 (d, 1H,
J = 4.5 Hz), 4.48 (d, 1H, J = 16.5 Hz), 4.23 (td, 1H, J =
2.4, 16.1 Hz), 3.74–3.72 (m, 1H), 3.48 (dd, 1H, J = 0.6,
3.6 Hz), 2.13 (s, 3H), 0.93 (s, 9H), 0.06 (s, 6H); 13C NMR
(75 MHz, CDCl3): d 192.7, 169.7, 139.0, 132.6, 64.1, 59.4,
55.2, 52.9, 25.8 (3C), 20.7, 18.3, ꢀ5.5 (2C); HRMS (ES)
m/z calcd for C15H24O5SiNa [M+Na]+: 335.1291, found
12. X-raydata for 26: X-raydata were collected at 293 K
on a BRUKER SMART APEX CCD diffractometer
with graphite monochromated MoKa radiation (k =
˚
25
0.7107 A). The structure was solved bydirect methods
335.1283; (+)-10 ½aꢂD +91.8 (c 0.25, H2O); 1H NMR
(SIR92). Refinement was done byfull-matrix least-squares
procedures on F2 using SHELXL-97. The non-hydrogen
atoms were refined anisotropicallywhereas hdyrogen
(300 MHz, D2O) d 5.70 (d, J = 5.4 Hz, 1H), 4.13 (dd,
J = 5.0 Hz, 1H), 4.09 (d, J = 15.6 Hz, 1H), 3.99 (d, J =
14.1 Hz, 1H), 3.93 (dd, J = 7.7, 0.6 Hz, 1H), 3.55 (dd,
J = 10.4, 7.7 Hz, 1H), 3.43 (dd, J = 10.8, 3.9 Hz, 1H);
13C NMR (75 MHz, CDCl3) d 144.9, 124.9, 75.3, 75.0,
atoms
MW = 222.2, colourless crystal, Crystal system: ortho-
were
refined
isotropically.
C12H14O4,
25
rhombic, space group: Pbca, cell parameters: a =
˚
73.4, 68.9, 64.0; (+)-20 ½aꢂD +45.2 (c 0.31, CHCl3); IR
˚
˚
8.415(2) A, b = 9.020 (2) A, c = 26.924 (7) A, V =
(neat) 1744 cmꢀ1 1H NMR (300 MHz, CDCl3) d 5.68–
;
2043.63(9) A , Z = 7, Dc = 1.26 g cmꢀ3, F(000) = 825.9,
3
˚
5.65 (m, 1H), 5.54 (m, 1H), 4.42 (s, 1H), 4.19(1/2 ABq,
J = 14.4 Hz, 1H), 4.08 (1/2 ABq, J = 14.4 Hz, 1H), 3.30–
3.28 (m, 1H), 3.24–3.23 (m, 1H), 2.11 (s, 3H), 0.91 (s, 9H),
0.88 (s, 9H), 0.17 (s, 3H), 0.15 (s, 3H), 0.05 (s, 3H), 0.04 (s,
3H); 13C NMR (75 MHz, CDCl3) d 170.4, 139.8, 115.4,
64.4, 63.6, 62.9, 53.4, 51.1, 25.8, 25.7, 21.0, 18.3, 18.0,
ꢀ4.4, ꢀ4.7, ꢀ5.3, ꢀ5.5; HRMS (ES) m/z calcd for
l = 0.095 mmꢀ1. Total number of l.s. parameters = 201,
R1 = 0.050 for 1747 Fo > 4 sig (Fo) and 0.062 for all 2089
data. wR2 = 0.105, GOF = 1.116, restrained GOF = 1.116
for all data. Crystallographic data have been deposited
with the Cambridge Crystallographic Data Centre, UK
(CCDC 260720). An ORTEP diagram (with 50% ellipsoi-
dal probability) is shown below.
C21H40O5Si2Na [M+Na]+: 451.2312, found 451.2329;
25
(+)-21 ½aꢂD +45.8 (c 1.07, CHCl3); IR (neat) 1743 cmꢀ1
;
1H NMR (300 MHz, CDCl3) d 5.71–5.69 (m, 1H), 5.58–
5.57 (m, 1H), 4.69 (s, 1H), 4.26 (1/2ABq, J = 15 Hz, 1H),
4.17 (1/2ABq, J = 14.6 Hz, 1H), 3.41–3.36 (m, 2H), 2.08
(s, 3H), 0.94 (s, 9H), 0.90 (s, 9H), 0.18 (s, 3H), 0.16 (s, 3H),
0.05 (s, 6H); 13C NMR (75 MHz, CDCl3) d 170.1,
141.1, 115.5, 66.2, 65.1, 63.0, 54.2, 52.7, 25.9, 25.7,
21.0, 18.3, 18.1, ꢀ4.2, ꢀ4.9, ꢀ5.3, ꢀ5.5; HRMS (ES)
m/z calcd for C21H40O5Si2Na [M+Na]+: 451.2312, found
25
451.2290; (ꢀ)-11 ½aꢂD ꢀ275.8 (c 0.33, C2H5OH); IR
(neat) 3352, 1673 cmꢀ1 1H NMR (300 MHz, CD3CO-
;
CD3) d 6.00 (d, J = 1.8 Hz, 1H), 4.54 (s, 1H), 4.47 (1/2ABq,
J = 16.8 Hz, 1H), 4.21 (1/2ABq, J = 18.3 Hz, 1H), 3.77