A stereodefined approach towards the bicyclo[3.3.1]nonan-9-one core of the phloroglucin natural products guttiferone A and hypersampsone F

Article abstract of DOI:10.1016/j.tetlet.2007.12.063

An approach towards the highly functionalized bicyclo[3.3.1]nonan-9-one core present in the phloroglucin natural products guttiferone A and hypersampsone F is disclosed in which the key C7 and C8 stereogenic centres have been successfully installed.

Full text of DOI:10.1016/j.tetlet.2007.12.063

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 1121–1124
A stereodefined approach towards the bicyclo[3.3.1]nonan-9-one
core of the phloroglucin natural products guttiferone
A and hypersampsone F
Goverdhan Mehta *, Mrinal K. Bera, Sandipan Chatterjee
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
Received 25 October 2007; revised 2 December 2007; accepted 12 December 2007
Abstract
An approach towards the highly functionalized bicyclo[3.3.1]nonan-9-one core present in the phloroglucin natural products guttifer-
one A and hypersampsone F is disclosed in which the key C7 and C8 stereogenic centres have been successfully installed.
Ó 2007 Elsevier Ltd. All rights reserved.
Polycyclic polyprenylated acyl phloroglucinols (PPAPs)
are a growing class of complex natural products that
embody a basic bicyclo[3.3.1]nonan-9-one framework with
varied substitution and stereochemical patterns.1,2 A nota-
ble feature of the PPAPs is the generous distribution of
isoprenoid fragments on the polyketide derived core struc-
ture and the wide ranging bioactivity profile exhibited by
many members of this family. An important sub-group
among PPAPs is represented by hyperforin 1,2a believed
to be responsible for much of the antidepressant activity
of Hypericum perforatum (St. John’s wort). In struc-
tural terms, hyperforin 1 has a prenyl group at C7 and a
quaternary centre at C8 bearing a homoprenyl moiety in
a well defined stereochemical disposition. Indeed setting-
up this stereochemistry is a challenge from total synthesis
perspectives.
ferone A 3 and hypersampson F 4, the C7 prenyl is endo and
the C8 homoprenyl is exo, although their trans relationship
is retained. Such subtle variation in stereochemistry at
remote C7 and C8 stereogenic centres is quite challenging
to negotiate from a synthetic point of view. Herein, we
report a synthetic approach that addresses the issue of the
C7, C8 stereochemistry and enables access to the core struc-
tures present in guttiferone A 3 and hypersampsone F 4.
This constitutes the first endeavor towards this sub-group
of complex, bioactive phloroglucin natural products.3,4
OH
O
O
9
OH
O
7
5
3
1
O
O
Several other phloroglucins such as furohyperforin 22b
share the C7, C8 stereodisposition with hyperforin 1, but,
there are other siblings including guttiferone A 3 (from
Symphonia globulifara, Guttiferae)2c,1 and hypersampsone
F 4 (from Hypericum sampsonii, Guttiferae),2f which display
diversified stereochemical orientation at these two stereo-
centres. Thus, the C7 prenyl (exo) and C8 homoprenyl
(endo) are trans in 1 and 2, but quite interestingly, in gutti-
O
O
Hyperforin (1)
Furohyperforin (2)
O
O
OH
O
O
O
O
O
OH
OH
Ph
*
Corresponding author. Tel.: +91 8023600367; fax: +91 8023600283.
Hypersampsone F (4)
Guttiferone A (3)
E-mail address: gm@orgchem.iisc.ernet.in (G. Mehta).
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.12.063

1122
G. Mehta et al. / Tetrahedron Letters 49 (2008) 1121–1124
Our synthetic approach towards guttiferone A 3 and
hypersampsone F 4 emanated from the readily available
racemic dimedone analogue 5, in which the key homo-
prenyl group bearing C8 quaternary centre is pre-installed
and whose facile synthesis from commercially available
citral has been outlined in the accompanying paper. The
1,3-dicarbonyl moiety in 5 was readily elaborated to methyl
enol ether 65 and further prenylation under kinetically con-
trolled conditions led to a diastereomeric mixture of enol
ethers 75 and 85 (1:1.2), Scheme 1. As anticipated, there
was only marginal diastereoselection during this alkylation
but the two stereogenic centres corresponding to C7 and
C8 of the target structures were now duly installed. Acid
mediated hydrolysis of 7 and 8 led to the readily separable
1,3-diketones 9 and 10, respectively.5
O
O
a
CO2Et
O
O
9
11
b
O
O
c
CO2H
O
O
O
13
12
d
Diastereomer 9 was subjected to one-pot, DBU pro-
moted tandem alkylations with 3-bromoethyl propionate
and prenyl bromide to furnish penta-alkylated 1,3-cyclo-
hexanedione 115 as a single diastereomer, Scheme 2. This
was a very pleasing outcome as we had envisaged stereo-
selection through 1,3-stereoinduction by the bystander pre-
nyl group. The prenyl group in 9 directs the sequential
alkylations from the opposite b-face and the order in which
the tandem protocol is implemented determines the stereo-
chemical outcome. In this case, realizing the requisite C7,
C8 stereochemistry of the target guttiferone A 3 mandated
that 9 was first subjected to propionate alkylation followed
by prenylation, Scheme 2. Ester hydrolysis of 11 to 12 and
enol-lactonization delivered enol lactone 135 to set the
stage for executing the retro-aldol–aldol protocol to deliver
O
OH
O
e
O
O
HO
15
14
Scheme 2. Reagents and conditions: (a) (i) 3-bromoethyl propionate,
DBU, THF, rt, 3 h; (ii) Me2C@CHCH2Br, DBU, THF, rt, 3 h, 45% (over
two steps); (b) concd HCl, acetone, H2O, 50 °C, 12 h, 87%; (c) NaOAc,
Ac2O, 140 °C, 1 h, 70%; (d) DIBAL-H, DCM, 0 °C, 2 h, 41%, (e) PCC,
DCM, 0 °C?rt, 1 h, 70%.
the bicyclo[3.3.1]nonanone framework. Towards this end,
enol lactone 13 was reduced with DIBAL-H to trigger
the desired structural rearrangement and furnish 14 with
concurrent reduction of the ketone carbonyl. PCC oxida-
tion of the diol readily furnished tricarbonyl compound
155 endowed with the core bicyclic framework of guttifer-
one A 3 and hypersampsone F 4 with requisite C7, C8
stereochemistry, Scheme 2. To fully secure the stereochem-
ical assignment in 15, its precursor enol lactone 13 was sub-
jected to controlled DIBAL-H reduction to furnish a
crystalline hydroxyl-dione 16 whose crystal structure was
determined,6 Figure 1.
Attention was now turned to diastereomer 10 and this
was subjected to the same protocol as 9 to generate the
bicyclo[3.3.1]nonan-9-one framework with predictable
and potentially useful outcome as displayed in Scheme 3.
Thus, tandem alkylations of 10 with 3-bromoethyl propio-
nate and prenyl bromide in the presence of DBU proceeded
with the expected 1,3-stereoinduction to furnish a single
diastereomer 17, Scheme 3. The pre-existing a-prenyl
group in the present case ensured the delivery of the second
prenyl group from the b-face to afford 17.5 Ester hydrolysis
of 17 to carboxylic acid 18 was routine but further enol-
lactonization in this case proved problematic. After some
trials, enol-lactone 19 could be obtained but this step needs
to be refined and improved further. Enol-lactone 195 was
subjected to DIBAL-H reduction to trigger the retro-
aldol/aldol cyclization process. In the event, the anticipated
O
O
a
OMe
OMe
O
O
5
6
b
O
O
+
OMe
7
8
c
d
O
O
O
9
10
Scheme 1. Reagents and conditions: (a) TiCl4, MeOH, 0 °C?rt, 1 h, 90%;
(b) LDA, Me2C@CHCH2Br, THF, À78 °C?0 °C, 12 h, 90%
(7:8 = 1:1.2); (c) concd HCl, acetone, H2O, rt, 12 h, 83%; (d) concd
HCl, acetone, H2O, rt, 12 h, 85%.

G. Mehta et al. / Tetrahedron Letters 49 (2008) 1121–1124
1123
chemical arrangement is quite interesting and has yet to
be encountered among the phloroglucin natural products.
In summary, we have delineated a concise strategy
towards the polyprenylated bicyclo[3.3.1]nonan-9-one core
present in guttiferone A 3 and hypersampsone F 4 in which
the installation of the key C7, C8 substituents with requi-
site stereochemistry has been realized. These results, in
conjunction with those described in the preceding
communication in the context of hyperforin, set the stage
for total synthesis endeavors towards this class of exotic
natural products.
Acknowledgements
One of us, M.K.B., thanks UGC for the award of a
research fellowship. We thank the CCD facility at IISc
for the single crystal X-ray diffraction data.
Fig. 1. The ORTEP diagram of hydroxyl-dione 16, obtained upon
controlled DIBAL-H reduction of 13. Displacement ellipsoids of all non-
hydrogen atoms have been drawn at 30% probability level. Hydrogen
atoms bonded to the disordered C8 homoprenyl group have not been
shown.
References and notes
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3986.
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B.; Cragg, G. M.; Boyd, M. R. Tetrahedron 1992, 48, 10093–10102; (d)
Shan, M. D.; Hu, L. H.; Chen, Z. L. J. Nat. Prod. 2001, 64, 127–130;
O
O
a
ˇ
´
´
(e) Savikin-Fodulovic, K.; Aljancic, I.; Vajs, V.; Menkovic, N.;
ˇ ´
CO2Et
´
´
Macura, S.; Gojgic, G.; Milosavljevic, S. J. Nat. Prod. 2003, 66,
1236–1238; (f) Lin, Y. L.; Wu, Y. S. Helv. Chim. Acta 2003, 86, 2156–
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Sterner, O.; Appendino, G.; Bombardelli, E. J. Org. Chem. 2004, 69,
7869–7874; (i) Gartner, M.; Mu¨ller, T.; Simon, J. C.; Giannis, A.;
Sleeman, J. P. ChemBioChem. 2005, 6, 171–177; (j) Herath, K.;
Jayasuriya, H.; Ondeyka, J. G.; Guan, Z.; Borris, R. P.; Stijfhoorn, E.;
Stevenson, D.; Wang, J.; Sharma, N.; Macnaul, K.; Menke, J. G.; Ali,
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Kingston, D. G. I. J. Nat. Prod. 2007, 70, 686–688.
O
O
17
10
b
O
O
c
CO2H
O
O
O
18
19
d
O
O
3. For synthetic studies toward PPAPs see: (a) Nicolaou, K. C.;
Pfefferkorn, J. A.; Kim, S.; Wei, H. X. J. Am. Chem. Soc. 1999, 121,
4724–4725; (b) Usuda, H.; Kanai, M.; Shibasaki, M. Org. Lett. 2002, 4,
859–862; (c) Usuda, H.; Kanai, M.; Shibasaki, M. Tetrahedron Lett.
2002, 43, 3621–3624; (d) Spessard, S. J.; Stoltz, B. M. Org. Lett. 2002,
4, 1943–1946; (e) Young, D. G. J.; Zeng, D. J. Org. Chem. 2002, 67,
3134–3137; (f) Kraus, G. A.; Nguyen, T. H.; Jeon, I. Tetrahedron Lett.
2003, 44, 659–661; (g) Takagi, R.; Nerio, T.; Miwa, Y.; Matsumura, S.;
Ohkata, K. Tetrahedron Lett. 2004, 45, 7401–7405; (h) Shimizu, Y.;
Kuramochi, A.; Usuda, H.; Kanai, M.; Shibasaki, M. Tetrahedron
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Shibasaki, M. J. Am. Chem. Soc. 2005, 127, 14200–14201; (j) Siegel, D.
R.; Danishefsky, S. J. J. Am. Chem. Soc. 2006, 128, 1048–1049; (k)
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5283–5285; (l) Nuhant, P.; David, M.; Pouplin, T.; Delpech, B.;
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Rodeschini, V.; Simpkins, N. S.; Ward, S. E.; Blake, A. J. J. Org.
Chem. 2007, 72, 4803–4815; (n) Nicolaou, K. C.; Carenzi, G. E. A.;
Jeso, V. Angew. Chem., Int. Ed. 2005, 44, 3895–3899.
HO
O
e
O
OH
20
21
Scheme 3. Reagents and conditions: (a) (i) 3-bromoethyl propionate,
DBU, THF, rt, 3 h; (ii) Me2C@CHCH2Br, DBU, THF, rt, 3 h, 40% (over
two steps); (b) concd HCl, acetone, H2O, 50 °C, 12 h, 87%; (c) NaOAc,
Ac2O, 140 °C, 1 h, 55%; (d) DIBAL-H, DCM, 0 °C, 2 h, 40%, (e) PCC,
DCM, 0 °C?rt, 1 h, 65%.
bicyclo[3.3.1]nonane diol mixture 20 was realized, Scheme
3. PCC oxidation of 20 delivered the bicyclic triketone
215 in which the C7 prenyl and C8 homoprenyl groups
were both endo- and cis-disposed. This unusual stereo-

1124
G. Mehta et al. / Tetrahedron Letters 49 (2008) 1121–1124
4. For our efforts in the area, see: (a) Mehta, G.; Bera, M. K. Tetrahedron
Lett. 2004, 45, 1113–1116; (b) Mehta, G.; Bera, M. K. Tetrahedron
Lett. 2006, 47, 689–692.
122.5, 117.9, 117.3, 51.9, 48.9, 40.3 (2C), 34.2, 27.3, 25.9, 25.8, 25.7,
24.6, 23.9, 23.5, 21.2, 17.9, 17.7, 17.6; HRMS (ES): m/z calcd for
C
26H38O3Na: 421.2719 (M+Na)+, found: 421.2717. Compound 15: IR
5. All new compounds reported here are racemic and were fully
characterized on the basis of their IR, 1H NMR, 13C NMR and mass
spectral data. Selected spectral data for key compounds: 6: IR (neat):
(neat): mmax 1715, 1700 cmÀ1; 1H NMR (300 MHz, CDCl3): d 5.16–5.12
(1H, m), 5.07–5.04 (1H, m), 4.88–4.85 (1H, m), 3.59 (1H, s), 2.50–2.34
(5H, m), 2.25–2.16 (2H, m), 2.05–1.94 (4H, m), 1.69 (3H, s), 1.66 (3H,
s), 1.63 (3H, s), 1.57 (3H, s), 1.56 (6H, s), 1.51–1.38 (2H, m), 0.77 (3H,
s); 13C NMR (75 MHz, CDCl3): d 209.8, 206.2, 204.9, 135.7, 132.9,
132.7, 122.9, 121.6, 117.4, 75.6, 63.6, 59.9, 43.0, 38.6, 37.7, 31.5, 27.6,
25.9, 25.8, 25.7, 22.3, 22.1, 18.5, 17.8, 17.7, 17.6; HRMS (ES): m/z
calcd for C26H38O3Na: 421.2719 (M+Na)+, found: 421.2733. Com-
mmax 1658, 1612 cmÀ1 1H NMR (300 MHz, CDCl3): d 5.36 (1H, s),
;
5.09–5.04 (1H, m), 3.69 (3H, s), 2.43–2.17 (4H, m), 1.97–1.92 (2H, m),
1.67 (3H, s), 1.59 (3H, s), 1.41–1.36 (2H, m), 1.05 (3H, s); 13C NMR
(75 MHz, CDCl3): d 199.4, 176.8, 131.8, 123.9, 100.5, 55.7, 49.2, 41.5,
41.0, 35.2, 25.7, 24.7, 22.4, 17.6; HRMS (ES): m/z calcd for
C14H22O2Na: 245.1517 (M+Na)+, found: 245.1515. Compound 7: IR
(neat): mmax 1660, 1619 cmÀ1; 1H NMR (300 MHz, CDCl3): d 5.28 (1H,
s), 5.20–5.16 (1H, m), 5.06–5.01 (1H, m), 3.67 (3H, s), 2.37–2.11 (5H,
m), 2.04–1.82 (2H, m), 1.68 (3H, s), 1.66 (3H, s), 1.59 (3H, s), 1.58 (3H,
s), 1.43–1.37 (2H, m), 0.99 (3H, s); 13C NMR (75 MHz, CDCl3): d
201.9, 174.8, 131.7, 124.0, 123.1, 100.4, 55.5, 55.3, 40.3, 39.3, 37.9, 25.7,
25.6, 24.5, 22.3, 22.2, 22.1, 17.8, 17.6; HRMS (ES): m/z calcd for
pound 17: IR (neat): mmax 1736, 1693 cmÀ1 1H NMR (300 MHz,
;
CDCl3): d 5.09–5.07 (1H, m), 4.99–4.95 (1H, m), 4.88–4.86 (1H, m),
4.10 (2H, q, J = 7.5 Hz), 2.67–2.34 (7H, m), 2.24–2.02 (5H, m), 1.95–
1.75 (1H, m), 1.68 (6H, s), 1.66 (3H, s), 1.62 (3H, s), 1.57 (3H, s), 1.55
(3H, s), 1.23 (3H, t, J = 7.2 Hz), 1.17 (3H, s), 1.17–1.10 (2H, m); 13C
NMR (75 MHz, CDCl3): d 208.6, 208.3, 173.1, 136.3, 132.1, 131.8,
123.4, 123.2, 116.3, 68.7, 59.9, 59.1, 49.7, 38.4, 36.7, 34.5, 29.5, 25.8,
25.6, 25.5, 25.4, 25.2, 21.9, 17.8, 17.7, 17.6, 17.3, 14.1; HRMS (ES): m/z
calcd for C28H44O4Na: 467.3137 (M+Na)+, found: 467.3129. Com-
C
19H30O2Na: 313.2144 (M+Na)+, found: 313.2149. Compound 8: IR
(neat): mmax 1658, 1616 cmÀ1; 1H NMR (300 MHz, CDCl3): d 5.25 (1H,
s), 5.15–5.05 (2H, m), 3.67 (3H, s), 2.44 (1H, 1/2 ABq, J = 18.0 Hz),
2.29–2.20 (1H, m), 2.17–2.05 (3H, m), 1.97–1.89 (2H, m), 1.68 (6H, s),
1.59 (3H, s), 1.57 (3H, s), 1.46–1.28 (2H, m), 1.05 (3H, s); 13C NMR
(75 MHz, CDCl3): d 202.2, 174.6, 132.1, 131.7, 124.1, 122.2, 100.1,
56.1, 55.5, 39.4, 38.1, 37.2, 25.7, 25.6, 25.3, 24.8, 21.7, 17.7, 17.5;
HRMS (ES): m/z calcd for C19H30O2Na: 313.2144 (M+Na)+, found:
pound 19: IR (neat): mmax 1767, 1715 cmÀ1 1H NMR (300 MHz,
;
CDCl3): d 5.38 (1H, s), 5.03–4.89 (3H, m), 2.65–2.58 (4H, m), 2.50–2.36
(2H, m), 2.08–1.96 (5H, m), 1.68 (3H, s), 1.65 (6H, s), 1.64 (3H, s), 1.55
(6H, s), 1.26 (3H, s), 1.22–1.16 (2H, m); 13C NMR (75 MHz, CDCl3): d
208.9, 168.2, 148.6, 136.2, 132.2, 131.9, 123.8, 122.9, 117.2, 117.1, 56.5,
48.9, 40.1, 38.4, 34.4, 28.1, 27.4, 25.9, 25.8, 25.6, 24.1, 23.2, 21.6, 18.1,
313.2168. Compound 9: IR (neat): mmax 1590, 1577 cmÀ1
;
1H NMR
17.9, 17.6; HRMS (ES): m/z calcd for
(M+Na)+, found: 421.2715. Compound 21: IR (neat): mmax 1715,
1699 cmÀ1 1H NMR (300 MHz, CDCl3): d 5.14–5.13 (1H, m), 4.90–
C26H38O3Na: 421.2719
(300 MHz, CDCl3): d 5.12–5.02 (2H, m), 3.38 (2H, br s), 2.69–2.35 (4H,
m), 2.45–2.18 (1H, m), 2.05–1.89 (2H, m), 1.68 (6H, s), 1.66 (3H, s),
1.59 (3H, s), 1.49–1.30 (2H, m), 0.84 (3H, s); 13C NMR (75 MHz,
CDCl3): d 204.6, 203.6, 133.1, 132.4, 123.1, 121.9, 58.0 (2C), 51.5, 40.4,
39.2, 25.8, 25.6, 22.9, 22.2, 21.7, 17.9, 17.6. Compound 10: IR (neat):
;
4.86 (2H, m), 3.58 (1H, s), 2.47–2.42 (4H, m), 2.37–2.33 (3H, m), 2.08–
1.98 (4H, m), 1.65 (3H, s), 1.63 (3H, s), 1.56 (12H, s), 1.42–1.34 (2H,
m), 1.31 (3H, s); 13C NMR (75 MHz, CDCl3): d 209.5, 205.4, 203.9,
135.4, 133.1, 132.2, 123.5, 121.7, 117.3, 78.8, 63.8, 63.3, 40.2, 38.3, 33.4,
31.3, 29.7, 28.2, 27.3, 25.9, 25.8, 25.7, 23.1, 22.9, 17.7, 17.6; HRMS
(ES): m/z calcd for C26H38O3Na: 421.2719 (M+Na)+, found: 421.2730.
6. Single crystal X-ray diffraction data were collected on a Bruker AXS
SMART APEX CCD diffractometer at 291 K. The X-ray generator
was operated at 50 kV and 35 mA using MoKa radiation. The data
were collected with an x scan width of 0.3°. A total of 606 frames per
set were collected using SMART in three different settings of u (0°, 90°
and 180°) keeping the sample to detector distance of 6.062 cm and the
2h value fixed at À25°. The data were reduced by SAINTPLUS; an
empirical absorption correction was applied using the package SADABS,
and XPREP was used to determine the space group. The structures were
solved using SIR92 and refined using SHELXL 97. Crystallographic data
has been deposited with the Cambridge Crystallographic Data
Centre, CCDC 664807. Crystal data for compound 16: C26H35O3,
mmax 1590, 1577 cmÀ1 1H NMR (300 MHz, CDCl3): d 5.10–4.99 (2H,
;
m), 3.36 (2H, d, J = 8.4 Hz), 2.71 (1H, 1/2 ABq, J = 15.0 Hz), 2.48–
2.27 (4H, m),1.94–1.88 (2H, m), 1.68 (3H, s), 1.67 (3H, s), 1.65 (3H, s),
1.58 (3H, s), 1.43–1.33 (2H, m), 1.04 (3H, s); 13C NMR (75 MHz,
CDCl3): d 204.9, 203.4, 133.5, 132.3, 123.3, 121.4, 60.4, 57.2, 51.0, 36.4,
35.9, 25.7, 25.6, 25.2, 23.5, 21.9, 17.8, 17.6; HRMS (ES): m/z calcd for
C18H28O2Na: 299.1987 (M+Na)+, found: 299.1987. Compound 11: IR
(neat): mmax 1737, 1694 cmÀ1; 1H NMR (300 MHz, CDCl3): d 5.06–5.04
(2H, m), 4.88–4.83 (1H, m), 4.09 (2H, q, J = 7.5 Hz), 2.97 (1H, 1/2
ABq, J = 15.3 Hz), 2.72–2.66 (1H, m), 2.57–2.49 (1H, m), 2.42–1.93
(10H, m), 1.67 (6H, s), 1.65 (6H, s), 1.59 (3H, s), 1.57 (3H, s), 1.49–1.41
(2H, m), 1.21 (3H, t, J = 7.2 Hz), 0.65 (3H, s); 13C NMR (75 MHz,
CDCl3): d 209.3, 208.9, 173.2, 136.5, 132.2, 131.9, 123.2, 123.0, 116.4,
68.7, 60.1, 54.4, 50.0, 40.5, 38.4, 36.3, 29.6, 25.9, 25.8, 25.7, 25.6, 25.4,
22.3, 21.8, 17.9, 17.7, 17.6, 14.1; HRMS (ES): m/z calcd for
28H44O4Na: 467.3137 (M+Na)+, found: 467.3136. Compound 13:
M = 395.54, triclinic, space group P1, a = 8.996(2) A, b = 12.056(3) A,
ꢀ
˚
˚
C
IR (neat): mmax 1768, 1716, 1681 cmÀ1; 1H NMR (300 MHz, CDCl3): d
5.35 (1H, s), 5.09–5.07 (1H, m), 5.00–4.90 (2H, m), 2.87–2.84 (1H, m),
2.64–2.33 (4H, m), 2.03–1.92 (6H, m), 1.69 (6H, s), 1.66 (6H, s), 1.61
(3H, s), 1.56 (3H, s), 1.40–1.21 (2H, m), 0.79 (3H, s); 13C NMR
(75 MHz, CDCl3): d 209.2, 168.1, 148.8, 136.1, 132.2, 132.1, 123.5,
c = 12.660(3) A, a = 71.812(4)°, b = 84.176(4)°, c = 69.777(4)°,
˚
3
V = 1223.9(5) A ,
Z = 2,
q
calcd = 1.073 g cmÀ3
,
F(000) = 430,
˚
l = 0.068 mmÀ1
,
T = 291 K, number of l.s. parameters = 300,
R = 0.0923, Rw = 0.2494, GOF = 1.021 for 2721 reflections with
I > 2r(I).