First total synthesis and reassignment of absolute configuration of diosniponol A and B

Article abstract of DOI:10.1016/j.tetlet.2014.04.065

Enantioselective first total synthesis of diosniponol A and B has been achieved starting from commercially available vanillin. Wittig reaction, Keck allylation, and Prins cyclization reactions are the key steps involved in the target synthesis.

Full text of DOI:10.1016/j.tetlet.2014.04.065

Accepted Manuscript
First total synthesis and reassignment of absolute configuration of diosniponol
A and B
J.S. Yadav, Vinay K. Singh, B. Thirupathaiah, A. Bal Reddy
PII:
S0040-4039(14)00690-X
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.04.065
TETL 44527
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
21 January 2014
16 April 2014
17 April 2014
Please cite this article as: Yadav, J.S., Singh, V.K., Thirupathaiah, B., Bal Reddy, A., First total synthesis and
reassignment of absolute configuration of diosniponol A and B, Tetrahedron Letters (2014), doi: http://dx.doi.org/
10.1016/j.tetlet.2014.04.065
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First total synthesis and reassignment of
absolute configuration of diosniponol A and B
J. S. Yadav *, Vinay K. Singh, B. Thirupathaiah, A. Bal Reddy
R
OH
OHC
OMe
OH
OMe
OBn
MeO
HO
OMe
OH
O
Vanillin
OH,
R=
R= OH,
A 1
Diosniponol
Diosniponol
2
B

Tetrahedron Letters
1
TETRAHEDRON:
LETTERS
Pergamon
First total synthesis and reassignment of absolute configuration of diosniponol
A and B.
J. S. Yadav,*,a,b Vinay K. Singh,a,b B. Thirupathaiah,b A. Bal Reddyb
(a) Academy of Scientific and Innovative Research ( b) Natural Products Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad- 500007,
India.
E-mail: yadavpub@iict.res.in; Fax: 91-40-27160512.
Abstract— Enantioselective first total synthesis of diosniponol A and B have been achieved starting from commercially
available vanillin. Wittig reaction, Keck allylation and Prins cyclization reactions are the key steps involved in the target
synthesis.
Keywords: Diosniponol A and B, anti-neuroinflammatory effects, Prins cyclization, Wittig reaction, Keck allylation.
R1
The compounds with diaryl motif are ubiquitous and attract
R
3
2
1
significant attention due to their impressive biological
activities like antidepressant,1 antifungal,2 antioxidative,3
and anticancer4 activities. Recently, Kang Ro Lee and co-
workers5 isolated two new cyclic diaryl heptanoids (with a
tetrahydropyran core) from rhizomes of D. nipponica and
named them as diosniponol A and B with some known
compounds. The diarylheptanoids exhibited anti-
neuroinflammatory5 and anti-inflammatory6 properties. The
mechanistic study revealed that diarylheptanoids and their
derivatives display anti-inflammatory properties by
inhibition of NO production in LPS-activated BV-2 cells.
The absolute stereochemistry of diosniponol A and B was
initially assigned based on 2D NMR studies7a-d and in
comparison with stereochemistry of compound 3 as 1 and
2. However, since the structure of 3 was later revised to its
enantiomeric form,7e we have chosen diosniponol A and B
as the target molecules for the total synthesis which allows
one to identify the absolute stereochemistry as well as aid
in evaluation of biological properties. Diosniponol A and B
have a common tetrahydropyran unit with three chiral
centers and differ at C3 position (figure 1) where the center
is inversed. Though, several methods are available for the
preparation of tetrahydropyran skeleton,8 Prins cyclization
constitutes a powerful synthetic method to construct the
4
7
2''
2'
1'
3'
1''
3''
MeO
HO
OMe
OH
O
5
O
6
HO
OH
1
OH, diosniponol A 1
OH, diosniponol B 2
R=
R=
R1=
R1=
OH,
OH,
3
4
Proposed structure
OH
R2
O
O
5
HO
OH
R2=
R2=
OH,
OH,
6
7
HO
OH
Figure 1. Representative example of cyclic diaryl
heptonoids
Retrosynthetic analysis is outlined in Scheme 1.
Accordingly, diosniponol
B can be accessed from
diosniponol A through an inversion reaction (Mitsunobu
reaction). Diosniponol 1 can be synthesized by Prins
cyclization reaction involving two paths (Path A or Path B)
via a Prins reaction involving a homoallyl alcohol 8 and an
aldehyde 9 (Path A) or aldehyde 10 and homoallyl alcohol
11 (Path B). All the four intermediate 8, 9, 10 and 11 are
easily accessible from inexpensive and readily available
vanillin.
tetrahydropyran core. In continuation of our efforts towards
exploring Prins cyclization9 reaction for the synthesis of
natural products, we herein describe the utility of Prins
reaction for the first total synthesis of diosniponol A and B.

2
Tetrahedron Letters
TFA ended up with the formation of compound 15 in major
MeO
TsO
OHC
OMe
OBn
amount (75%) along with compound 16 in minor amount
(10%). The major product was attributed due to the allyl
transfer through the 2-oxonia Cope Rearrangement13
(directly from homoallylic alcohol 8 or by benzylic cation
A) as precedented earlier wherein intermediate 11 was
formed. We presume that the allyl transfer14 product 11
now undergo Prins cyclization with aldehyde 9 to yield 15
(Scheme 3).
OH
+
8
9
2 steps
OHC
4 steps
5 steps
Path A
OMe
OH
Prins
cyclization
2
1
Vanillin
1 step
Path B
MeO
TsO
CHO
OMe
OBn
HO
+
Prins
cyclization
9
H2O
O
10
8
16
11
TsO
OBn
TsO
B
OMe
OMe
OMe
Scheme 1. Retrosynthetic analysis of diosniponol A and B
e
p
A
o
C
-
a
i
n
o
x
Initially, we focused on path A, where the synthesis starts
with protection of phenolic hydroxyl group of vanillin with
tosyl chloride in triethyl amine and CH2Cl2 to provide 10.
Compound 10 on Keck allylation10 with allyl-SnBu3 in
presence of (S)-BINOL afforded homoallylic alcohol 8 (ee
85%).11 Simultaneously, for the aldehyde fragment 9,
vanillin was subjected to homologation with stabilized
O
-
2
O
+
O
HO
H2O
TsO
OMe
TsO
OBn
OBn
11
C
OMe
OMe
OMe
9
Prins
cyclization
OH
Wittig
ylide
{(ethoxycarbonylmethylene)
triphenylphosphorane} in anhydrous benzene under
refluxed condition to afford α,β-unsaturated ester 12 in
95% yield (Scheme 2). Compound 12 was reduced with
NiCl2.6H2O12 and NaBH4 to furnish saturated ester 13 in
92% yield. Benzyl protection of phenolic alcohol with
benzyl bromide and NaH in THF afforded compound 14.
O
BnO
OBn
15
OMe
OMe
o
o
Scheme 3. Reagents and conditions: (a) TFA, CH2Cl2, 0
C, 18 h, then K2CO3, MeOH, 85%.
The ester 14 was reduced by DIBAL-H at -78 C to give
aldehyde 9 in 92% yield.
CHO
With the disappointing results obtained for path A, we
proceeded further for path B. Accordingly, (Scheme 4)
compound 9 was subjected to Keck allylation10 to afford
homoallylic alcohol 11 (ee 95%)15 and the absolute
configuration of compound 11 was established by using the
Mosher’s method16(see supporting information).
Compound 11 was treated with aldehyde 10 in presence of
TFA to yield 16 in 67% yield along with minor by product
15 in 20% yield.
O
MeO
MeO
TsO
b
a
H
OH
OMe
TsO
OH
Vanillin
10
8
c
O
O
d
e
OMe
OH
OMe
OH
EtO
EtO
EtO
13
12
O
O
OMe
OBn
OH
OMe
OBn
f
H
a
b
14
HO
9
9
O
15
OBn
TsO
OBn
16
11
OMe
Scheme 2. Reagents and conditions: (a) Et3N, TsCl,
OMe
OMe
o
CH2Cl2, 0 C to rt, 8 h, 93%; (b) (S)-BINOL, Ti(i-OPr)4,
o
allyl-SnBu3, CH2Cl2, molecular sieves 4-Å, -20 C, 72 h,
o
80%; (c) Ph3P=CHCOOEt Benzene, 80 C, 4 h, 95%; (d)
NiCl2.6H2O, NaBH4, MeOH, 0 oC to rt, 4 h, 92%; (e) NaH,
BnBr, THF 0 oC to rt, 8 h, 93%; (f) DIBAL-H, -78 oC, 2 h,
92%.
Scheme 4. Reagents and conditions: (a) (R)-BINOL, Ti(i-
OPr)4, allyl-SnBu3, CH2Cl2, molecular sieves 4-Å, -20 C,
72 h, 85%; (b) 10, TFA, CH2Cl2, 0 C, 16 h, then K2CO3,
o
o
MeOH, 87%.
With the two key fragments in hand, the stage was set for
proceeding further towards Prins cyclization reaction.
However, our attempts for cyclization with 8 and 9 with

Tetrahedron Letters
References and Notes
3
OH
O
OH
b
a
16
O
(1) Ameen, D.; Snape, J. T.; Med. Chem. Commun. 2013, 4,
893.
(2) Endo, K.; Kanno, E.; Oshima, Y. Phytochemistry 1990,
29, 797.
1
HO
OBn
HO
OH
OMe
OMe
OMe
OMe
17
c
OH
(3) Jitoe, A.; Masuda, T.; Mabry, T. J. Tetrahedron Lett.
1994, 35, 981.
(4) Huang, M. T.; Smart, R. C.; Wong, C. Q.; Conney, A.
H. Cancer Res. 1988, 48, 5941.
(5) Woo, K. W.; Moon, E.; Kwon, O. W.; Lee, S. O.; Kim,
S. Y.; Choi, S. Z.; Son, M. W.; Lee, K. R.; Bioorg. Med.
Chem. Lett. 2013, 23, 3806.
(6) (a) Lee, C. J.; Lee, S. S.; Chen, S. C.; Ho, F. M.; Lim,
W. W. Br. J. Pharmacol. 2005, 146, 378; (b) Lee, M. A.;
Lee, H. K.; Kim, S. H.; Kim, Y. C.; Sung, S. H. Planta
Med. 2010, 76, 1007; (c) Lee, K. Y.; Kim, S. H.; Sung, S.
H.; Kim, Y. C. Planta Med. 2008, 74, 867
(7) (a) Dong, S.-H.; Nikolic, D.; Simmler, C.; Qiu, F.; Van
Breemen, R. B.; Soejarto, D. D.; Pauli, G. F.; Chen, S.-N.
J. Nat. Prod. 2012, 75, 2168; (b) Kikuzaki, H.; Nakatani,
N. Phytochemistry 1996, 43, 273; (c) Tao, Q. F.; Xu, Y.;
Lam, R. Y. Y.; Schneider, B.; Dou, H.; Leung, P. S.; Shi, S.
Y.; Zhou, C. X.; Yang, L. X.; Zhang, R. P.; Xiao, Y. C.;
Wu, X.; Stockigt, J.; Zeng, S.; Cheng, C. H. K.; Zhao, Y. J.
Nat. Prod. 2008, 71, 12; (d) Wu, H.-C; Cheng, M.-J.; Peng,
C.-F.; Yang, S.-C.; Chang, H.-S.; Lin, C.-H.; Wang, C.-J.;
Chen, I.-S. Phytochemistry 2012, 82, 118; (e) Dong, S.-H.;
Nikolic, D.; Simmler, C.; Qiu, F.; Van Breemen, R. B.;
Soejarto, D. D.; Pauli, G. F.; Chen, S.-N. J. Nat. Prod.
2013, 76, 2005.
O
HO
OH
OMe
OMe
2
Scheme 5. Reagents and conditions: (a) K2CO3, MeOH
reflux, 91%; (b) H2, Pd(OH)2, THF, 4 h, 92%; (c) DEAD,
TPP, p-NO2-C6H4CO2H then K2CO3, MeOH, 90%.
Detosylation of 16 with K2CO3 in MeOH under reflux
condition provided compound 17 in 91% yield. Finally,
debenzylation was achieved by exposure of 17 to Pd(OH)2
in H2 atmosphere to afford diosniponol A (1) in 92% yield.
Diosniponol A was subjected to Mitsunobu inversion17
reaction followed by hydrolysis to yield diosniponol B (2)
in 90 % yield. The spectral data of our synthetic
compounds 1 and 2 were found to be similar to the data of
natural diosniponol A, B. However the optical rotation of
synthesised diosniponol A, B were found to be of opposite
signs when compared to isolated natural products.
diosniponol A, [α]D = +4.8 (c 0.060, CH3OH)5; synthetic
25
25
diosniponol A, [α]D = -10.8 (c 0.06, CH3OH); natural
diosniponol B, [α]D25 = +0.8 (c 0.0050, CH3OH)5; synthetic
25
diosniponol B, [α]D = -3.8 (c 0.005, CH3OH). Our
synthesis
unambiguously
confirms
the
absolute
(8) for review (a) Clarke, P. A.; Santos, S.; Eur. J. Org.
Chem. 2001, 2045; (b) Fuwa, H. Hetereocycles 2012, 85,
1255.
stereochemistry of natural product diosniponol A and B as
1a and 2a respectively, since we ended with their
enantiomers (Figure 2).
(9) (a) Yadav, J. S.; Reddy, N. M.; Reddy, P. A. N.; Ather,
H.; Prasad, A. R. Synthesis 2010, 1473; (b) Yadav, J. S.;
Reddy, Y. J.; Reddy, P. A. N.; Reddy, B. V. S. Org. Lett.
2013, 15, 546; (c) Reddy, B. V. S.; Reddy, B. P.;
Pandurangam, T.; Yadav, J. S. Tetrahedron Lett. 2011,
52, 2306; (d) Reddy, B. V. S.; Reddy, B. P.; Reddy, P. S.;
Reddy, Y. J.; Yadav, J. S. Tetrahedron Lett. 2013, 54,
4960; (e) Yadav, J. S.; Reddy, M. S.; Rao, P. P.; Prasad, A.
R. Tetrahedron Lett. 2006, 47, 4397; (f) Yadav, J. S.;
Reddy, P. A. N.; Kumar, A. S.; Prasad, A. R.; Reddy, B. V.
S.; Ghamdi, A. A. Al Tetrahedron Lett. 2014, 55. 1395 (g)
Swapnil, N.; Venkatesh, M.; Prasad, A. R. Tetrahedron
Lett. 2014, 55, 1164.
(10) (a) Keck, G. E.; Tarbet, K. H.; Geraci, L. S. J. Am.
Chem. Soc. 1993, 115, 8467; (b) Keck, G. E.;
Krishnamurthy, D. Org. Synth. 1998, 75, 12; (c) Reddy, C.
R.; Rao, N. N.; Srikanth, B. Eur. J. Org. Chem. 2010, 345
(11) Enantiomeric excess (ee) of homoallylic alcohol 11
was, determined by chiral HPLC [Eurocel-02, 250×4.6
mm, 5 μ, 15% i-PrOH in hexanes, flow rate 1.0 mL/min,
retention time 9.51 (7.41 %), 10.87 (92.59 %).
OH
OH
MeO
HO
OMe
OH
MeO
HO
OMe
OH
O
O
Diosniponol A 1a
Diosniponol B 2a
Revised structure of diosniponol
Figure 2.
In summary, we herein report the concise and
straightforward, reliable and convergent approach for the
synthesis of diosniponols A and B. The key steps involved
in this synthesis are Keck allylation, Prins cyclization and
Mitsunobu inversion.
Acknowledgements
V.K.S and B.T thank UGC and A.B.R thanks CSIR New
Delhi, India, for the award of fellowships. The authors
thank B. Manjula, Natural Products Chemistry Division,
CSIR-IICT for their help in HPLC studies. JSY thank CSIR
and DST for the award of Bhatnagar and J C Bose
Fellowships respectively.
(12) Satoh, T.; Nanba, K.; Suzuki, S. Chem. Pharm. Bull.
1971, 19, 817.

4
Tetrahedron Letters
(13) (a) Nokami, J.; Yoshizane, K.; Matsuura, H.; Sumida,
S. I. J. Am. Chem. Soc. 1998, 120, 6609; (b) Sumida, S.-I.;
Ohga, M.; Mitani, J.; Nokami, J. J. Am. Chem. Soc. 2000,
122, 1310; (c) Loh, T.-P.; Hu, Q.-Y.; Ma, L.-T. J. Am.
Chem. Soc. 2001, 123, 2450; (d) Loh, T.-P.; Ken Lee, C.-
L.; Tan, K.-T. Org. Lett. 2002, 4, 2985; (e) Loh, T.-P.; Hu,
Q.-Y.; Ma, L.-T. Org. Lett. 2002, 4, 2389; (f) Lee, C.-L. K.;
Lee, C.-H. A.; Tan, K.-T.; Loh, T.-P. Org. Lett. 2004, 6,
1281; (g) Chen, Y.-H.; McDonald, F. E. J. Am. Chem. Soc.
2006, 128, 4568.
(14) For allyl transfer and 2-oxonia-Cope rearrangements
as competing processes in Prins cyclizations, see: (a)
Lolkema, L. D. M.; Semeyn, C.; Ashek, L.; Hiemstra, H.;
Speckamp, W. N. Tetrahedron 1994, 50, 7129; (b) Roush,
W. R.; Dilley, G. J. Synlett 2001, 955; (c) Rychnovsky, S.
D.; Marumoto, S.; Jaber, J. J. Org. Lett. 2001, 3, 3815; (d)
Crosby, S. R.; Harding, J. R.; King, C. D.; Parker, G. D.;
Willis, C. L. Org. Lett. 2002, 4, 577; (e) Crosby, S. R.;
Harding, J. R.; King, C. D.; Parker, G. D.; Willis, C. L.
Org. Lett. 2002, 4, 3407; (f) Hart, D. J.; Bennet, C. E. Org.
Lett. 2003, 5, 1499; (g) Jasti, R.; Anderson, C. D.;
Rychnovsky, S. D. J. Am. Chem. Soc. 2005, 127, 9939; (h)
Jasti, R.; Rychnovsky, S. D. J. Am. Chem. Soc. 2006, 128,
13640.
114.2, 112.3, 74.4, 71.2, 68.1, 55.9, 41.3, 37.9, 31.5 ppm;
HRMS calculated for C37H42O6Na [M + Na]+ 605.2868,
found 605.2879. Diosniponol
A
(1) Rf
=
0.48
25
(hexane:EtOAc, 5:5); [α]D = -10.8 (c 0.06, CH3OH); IR
(neat) υmax: 3423, 2940, 1606, 1515, 1270, 1033, 754 cm-1;
1H NMR (300 MHz, CD3COCD3): δ 7.44 (s, 1H), 7.26 (s,
1H), 7.0 (d, J = 1.8 Hz, 1H), 6.84 (dd, J = 1.8, 8.1 Hz, 1H),
6.79 (d, J = 1.9 Hz, 1H), 6.78 (d, J = 8.1 Hz, 1H), 6.70 (d, J
= 7.9 Hz, 1H ), 6.63 (dd, J = 1.9, 8.1 Hz, 1H), 4.27 (dd, J =
1.9, 11.4 Hz, 1H), 3.84 (s, 3H), 3.88-3.80 (m, 1H), 3.79 (s,
3H), 3.46-3.40 (m, 1H), 2.73-2.60 (m, 2H), 2.13-2.07 (m,
1H), 1.97-1.92 (m, 1H), 1.88-1.81 (m, 1H), 1.78-1.71 (m,
1H), 1.41-1.29 (m, 1H), 1.25-1.16 (m, 1H) ppm; 13C NMR
(100 MHz, CD3COCD3): δ 148.2, 148.1, 146.6, 145.5,
135.7, 134.5, 121.6, 119.5, 115.6, 115.5, 112.8, 110.6, 78.2,
75.6, 68.5, 56.3, 56.2, 44.5, 42.2, 39.1, 32.1 ppm; HRMS
calculated For C21H26O6Na [M + Na]+ 397.1621, found
397.1691. Diosniponol B (2) Rf = 0.47 (hexane:EtOAc,
25
5:5); [α]D = -3.8 (c 0.005, CH3OH); IR (neat) υmax: 3423,
1
2940, 1606, 1515, 1270, 1033, 754 cm-1; H NMR (300
MHz, CD3COCD3): δ 7.41 (s, 1H), 7.25 (s, 1H), 6.99 (d, J
= 1.8 Hz, 1H), 6.84-6.79 (m, 2H), 6.78 (d, J = 8.0 Hz, 1H),
6.71 (d, J = 8.1 Hz, 1H), 6.64 (dd, J = 1.9, 8.1 Hz, 1H),
4.74 (dd, J = 1.9, 11.6 Hz, 1H), 4.23 (bs, 1H), 3.95-3.88
(m, 1H), 3.84 (s, 3H), 3.78 (s, 3H), 2.71-2.59 (m, 2H),
1.88-1.83 (m, 1H), 1.82-1.74 (m, 1H), 1.73-1.63 (m, 3H),
1.54-1.47 (m, 1H) ppm. 13C NMR (100 MHz, CD3COCD3):
δ 147.2, 147.1, 145.5, 144.5, 135.5, 133.7, 120.6, 118.3,
114.7, 114.5, 112.0, 109.6, 73.2, 70.7, 63.8, 55.3, 55.1,
40.9, 38.5, 38.3, 31.0 ppm; HRMS calculated For
C21H26O6Na [M + Na]+ 397.1621, found 397.1691.
(15) Enantiomeric excess (ee) of allylic alcohol 11 was,
determined by chiral HPLC [Eurocel-02, 250x4.6 mm, 5 μ,
25% iPrOH in hexanes, flow rate 1.0 mL/min, retention
time 15.470 (2.48 %), 18.72 (97.52 %).
(16) (a) Dale, J. A.; Mosher, H. S. J. Am. Chem. Soc. 1968,
90, 3732 (b) Dale, J. A.; Dull, D. L.; Mosher, H. S. J. Org.
Chem. 1969, 34, 2543 (c) Seco, J. M.; Quinoa, E.; Riguera,
R. Chem. Rev. 2004, 104, 17.
(17) Mitsunobu, O. Synthesis 1981, 1.
(18) Spectral data for selected compounds. Compound
28
(16) Rf = 0.50 (hexanes:EtOAc, 5:5); [α]D = -14.5 (c 0.5,
CHCl3); IR (neat) υmax: 3456, 2962, 2927, 2855, 1726,
1
1458, 1362, 1176, 1098, 949 cm-1; H NMR (300 MHz,
CDCl3: δ 7.77 (d, J = 8.30 MHz, 2H), 7.31-7.27 (m, 6H),
7.09 (d, J = 8.30 MHz, 1H), 6.92-6.62 (m, 5H), 5.12 (s,
2H), 4.33-4.26 (m, 1H), 3.97-3.82 (m, 1H), 3.83 (s, 3H),
3.59 (s, 3H), 3.50-3.38 (m, 1H), 2.76-2.59 (m, 2H), 2.44 (s,
3H), 2.25-2.14 (m, 1H), 2.07-1.66 (m, 3H), 1.47-1.22 (m,
3H) ppm; 13C NMR (75 MHz, CDCl3): δ 151.7, 149.5,
146.3, 144.9, 142.3, 137.5, 137.3, 135.1, 133.3, 129.3,
128.5, 128.4, 127.7, 127.2, 123.7, 120.2, 117.8, 114.1,
112.3, 110.2, 76.2, 74.8, 71.1, 68.2, 55.9, 55.5, 42.8, 40.7,
37.5, 31.2, 21.6 ppm; HRMS calculated for C35H38O8NaS
[M + Na]+ 641.2178, found 641.2179.
Compound (15) Light yellow solid, M.P. 121 oC; Rf = 0.52
(hexanes:EtOAc, 5:5); IR (KBr) υmax: 3257, 2937, 2861,
1516, 1259, 1136,1030, 745, 689 cm-1; 1H NMR (300 MHz,
CDCl3: δ 7.44 (d, J = 7.4 Hz, 4H), 7.38-7.33 (m, 4H), 7.31-
7.27 (m, 2H), 6.80 (d, J = 8.2 Hz, 2H), 6.75 (d, J = 1.9 Hz,
2H), 6.66 (dd, J = 1.9, 8.0 Hz, 2H), 5.14 (s, 4H), 3.88 (s,
6H), 3.80-3.72 (m, 1H), 3.30-3.22 (m, 2H), 2.84-2.74 (m,
2H), 2.68-2.60 (m, 2H), 1.95-1.86 (m, 4H), 1.78-1.67 (m,
2H), 1.28-1.13 (m, 2H) ppm; 13C NMR (75 MHz, CDCl3):
δ 149.5, 146.3, 137.3, 135.3, 128.4, 127.7, 127.2, 120.2,