Regioselective oxidative cleavage of benzylidene acetals: synthesis of highly functionalized chiral intermediates

Article abstract of DOI:10.1016/j.tetlet.2006.12.078

A mild and efficient method for the regioselective oxidative cleavage of benzylidene acetals with KBrO₃/Na₂S₂O₄ under bi-phasic conditions (EtOAc/H₂O), leading to highly functionalized chiral intermed

Full text of DOI:10.1016/j.tetlet.2006.12.078

Tetrahedron Letters 48 (2007) 1175–1178
Regioselective oxidative cleavage of benzylidene acetals:
synthesis of highly functionalized chiral intermediates
Pon Minor Senthilkumar, Appu Aravind and Sundarababu Baskaran*
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India
Received 15 October 2006; revised 3 December 2006; accepted 13 December 2006
Available online 8 January 2007
Abstract—A mild and efficient method for the regioselective oxidative cleavage of benzylidene acetals with KBrO3/Na2S2O4 under
bi-phasic conditions (EtOAc/H2O), leading to highly functionalized chiral intermediates, is reported.
Ó 2006 Published by Elsevier Ltd.
1. Introduction
tive and reductive conditions, recently resulted in the
synthesis of highly functionalized chiral intermediates
and their further application in the stereoselective syn-
thesis of biologically active and pharmaceutically impor-
tant molecules.3
Chemoselective transformation of multifunctional
organic compounds is a synthetic challenge for organic
chemists and success depends on efficient manipulation
of the functional groups involved. The selective protec-
tion and deprotection of polyhydroxylated substrates
is a key step in the chemical synthesis of complex mole-
cules.1 Benzylidene acetals are widely used in organic
synthesis due to their tolerance to a wide variety of
reagents and reaction conditions.2 Regioselective
reductive3 as well as oxidative cleavage of benzylidene
acetals are important as they lead to synthetically useful
intermediates. Benzylidene acetals can be oxidatively
In this Letter, we report a highly regioselective method
for the oxidative cleavage of benzylidene acetals to novel
chiral intermediates using the potassium bromate–
sodium dithionite reagent system. Following the reported
procedure,11 we initially studied the regioselective oxida-
tive cleavage of bis-benzylidene acetal 1a with sodium
bromate–sodium dithionite under bi-phasic (EtOAc/
H2O) conditions. However, unfortunately, this reaction
resulted in the isolation of diol 2a in a low yield with a
poor regioselectivity. In order to improve the yield and
regioselectivity, we investigated several variables, such
as temperature, stoichiometry of the reagents (KBrO3/
Na2S2O4), and volume of the solvent. After much exper-
imentation, we realized that the volume of ethyl acetate
plays a key role in deciding the yield and regioselectivity
of the reaction (Table 1). Under the modified reaction
conditions (entry 3), oxidative cleavage of bis-benzyli-
dene acetal 1a gave terminal diol 2a as the major prod-
uct and internal diol 3a as a minor product in an 88%
yield (86:14). Notably, the other possible product was
not observed under the reaction conditions (Scheme 1).
cleaved using trityl fluoroborate (Ph3CþBF ꢀ),4 ozone,5
4
pyridinium dichromate/t-butyl hydroperoxide,6 NBS/
H2O,7 NaBO3,8 Co(OAc)2/N-hydroxyphthalimide9 and
2,20-bipyridinium chlorochromate/m-CPBA.10 Iadonisi
and co-workers11 have reported a new method for the
deprotection of benzyl ethers in carbohydrate substrates
using the sodium bromate–sodium dithionite reagent
system under bi-phasic conditions. During the course
of their studies, they also observed the oxidative cleav-
age of benzylidene acetal under the reaction conditions.
However, the synthetic potential of sodium bromate–
sodium dithionite as a novel reagent system for the
regioselective oxidative cleavage of benzylidene acetals
was not fully explored.
In order to test the efficiency of our modified conditions,
the regioselective oxidative cleavage was attempted
with the known substrate 411 and the results are
shown in Scheme 2. Under our modified conditions,
we achieved a better regioselectivity (77:23) compared
to the reported procedure (65:35).11
Our continued interest in the regioselective cleavage of
bis-benzylidene acetals of D-mannitol under both oxida-
*
Corresponding author. Tel.: +91 44 2257 5280; fax: +91 44 2257
0545; e-mail: sbhaskar@iitm.ac.in
0040-4039/$ - see front matter Ó 2006 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2006.12.078

1176
P. M. Senthilkumar et al. / Tetrahedron Letters 48 (2007) 1175–1178
Table 2. Regioselective oxidative cleavage of bis-benzylidene acetalsa
Table 1. Effect of concentration on the oxidative cleavage of 1a
Entry
Substrate
Volume of
EtOAc (mmol)
Yieldb
(%)
Selectivity
(2a:3a)
Entry Substrate
Product
Yieldb,c (%)
RO
OBz OH
Ph
1
2
3
4
15a
20
25
30
67
75
88
86
76:24
78:22
86:14
86:14
RO
O
O
1a
1
OH OBz OR
73
75
O
O
OR
2b R = Ms,
2c R = Ac
a Reported conditions.11
b Isolated yield of the mixture of isomers.
Ph
1b R = Ms,
1c R = Ac
TBDPSO
OBz OH
Ph
Ph
TBDPSO
OBz OH
TBDPSO
O
O
O
OH OBz OTBDPS
TBDPSO
O
O
O
KBrO3 / Na2S2O4
2
75
2a
OH OBz OMs
O
OMs
EtOAc / H2O, rt,
45 min, 88%
+
O
OTBDPS
2d
Ph
TBDPSO
OH OBz
1d
Ph
1a
OBz OH OTBDPS
Ph
HO
OBz
O
3a
O
O
Ph
O
O
BzO
HO
3
76
Scheme 1. Regioselective oxidative cleavage of bis-benzylidene acetals.
OMe
OMe
8
7
a Reaction time: 30–45 min.
HO
O
b Isolated yield of the major isomer.
c In addition, the minor regioisomer was isolated in 3–15% yield.
BzO
AcO
Ph
O
KBrO3 / Na2S2O4
OAc
OMe
O
O
5
AcO
EtOAc / H2O, rt,
30 min, 90%
(5:6 = 77:23)
+
ious sensitive functional groups and the results are
summarized in Table 3.
BzO
HO
O
AcO
OMe
4
AcO
OAc
Benzylidene acetals 9a, 17 and 19 having labile TBDPS
ether groups, underwent smooth reaction to give
primary alcohols 10a, 18 and 20, respectively, in good
yields. Benzylidene acetal 11, having reactive iodide
and mesylate functional groups, underwent facile oxida-
tive cleavage to give highly functionalized chiral deriva-
tive 12. Under similar reaction conditions, benzylidene
acetals 13 and 21, having sensitive functional groups,
reacted readily to give the corresponding chiral azido
alcohols 14 and 22, respectively, in good yields. Interest-
ingly, benzylidene acetal 15, possessing a malonate ester
and an OMs group, underwent a clean oxidative cleav-
age to give the corresponding chiral alcohol 16 in a good
yield.
OMe
6
Scheme 2. Regioselective oxidative cleavage of mono-benzylidene
acetals.
After successful modification of the reaction conditions,
the generality of this methodology was tested with sev-
eral bis-benzylidene acetals and the results are summa-
rized in Table 2.
A high degree of regioselectivity was observed when the
method was applied to both symmetrical and unsym-
metrical (Table 2, entries 1 and 2) bis-benzylidene ace-
tals derived from D-mannitol. Benzylidene acetals 1a–c
having labile functional groups such as TBDPS, OMs
and OAc underwent smooth oxidative cleavage to give
the corresponding C2-symmetric terminal diols 2a–c,
respectively, in good yields. Conspicuously, the migra-
tion of the silyl group or acetate was not observed under
the reaction conditions. Unsymmetrical benzylidene
acetal 1d underwent a smooth oxidative cleavage to give
the corresponding highly functionalized diol 2d in good
yield. Furthermore, substrate 7 having both five- and
six-membered benzylidene acetals (Table 2, entry 3), de-
rived from methyl-a-D-mannopyranoside, underwent
smooth oxidative cleavage to give diol 8 in good yield.
In conclusion, under the modified reaction conditions,
KBrO3–Na2S2O4 was found to be a very efficient and
mild reagent system for the regioselective oxidative
cleavage of both bis- and mono-benzylidene acetals,
leading to highly functionalized chiral intermediates in
very good yields.12 Synthetic application of this novel
oxidative cleavage reaction in the stereoselective synthe-
sis of biologically active molecules is in progress.
2. Experimental
Our modified oxidative cleavage procedure was also
tested with chiral mono-benzylidene acetals having var-
A typical experimental protocol for the regioselective
oxidative cleavage of benzylidene acetal is as follows:

P. M. Senthilkumar et al. / Tetrahedron Letters 48 (2007) 1175–1178
1177
26
Table 3. Regioselective oxidative cleavage of mono-benzylidene
white foamy solid. Mp 180–184 °C (CHCl3). ½aꢁD
1451, 1278, 1177, 1111, 741, 702, 675, 664, 509 cmꢀ1
acetalsa
+74.5 (c 1.0, CHCl3); IR (CHCl3): 2931, 2857, 1725,
Yieldb,c
(%)
;
Entry Substrate
Product
1H NMR [400 MHz, CDCl3] d: 7.93 (m, 4H), 7.68 (m,
2H), 7.62 (m, 2H), 7.53 (m, 4H), 7.36 (m, 10H), 7.24
(m, 4H), 7.15 (m, 4H), 5.70 (d, J = 4.2 Hz, 2H), 3.79
(dd, J = 7.9, 3.9 Hz, 2H), 3.57 (m, 4H), 1.10 (s, 18H);
13C NMR [100 MHz, CDCl3] d: 166.0, 135.9, 135.7,
133.8, 133.1, 132.3, 129.8, 129.8, 129.7, 129.5, 128.2,
127.6, 127.5, 72.6, 72.2, 62.5, 26.9, 19.2. HRMS (ESI)
calcd for C52H59O8Si2 (M+H)+: 867.3749. Found:
867.3781.
OBz
Ph
O
O
OR
OH
RO
RO
OR
1
9a R = TBDPS,
9b R = TBDMS,
9c R = Ms,
10a R = TBDPS,
10b R = TBDMS,
10c R = Ms,
77
78
77
74
9d R = Ac
10d R = Ac
OBz
OH
Ph
O
I
O
OMs
Acknowledgements
2
3
76
I
OMs
11
We thank the CSIR, New Delhi, for the financial
support. M.S.K. and A.A. thank CSIR, New Delhi,
for research fellowships.
12
OBz
Ph
O
O
OH
76
N3
N3
N3 N3
References and notes
13
14
1. (a) Greene, T. W.; Wuts, P. G. M. Protective Groups in
Organic Synthesis; John Wiley & Sons: New York, 1999;
Ph
O
MeO2C
OBz
O
OMs
´
(b) Kocienski, P. J. In Protecting Groups; Enders, R.,
MeO2C
MeO2
C
OH
4
5
6
7
73
72
67
73
Noyori, R., Trost, B. M., Eds.; Thieme: Stuttgart, 1994,
Chapter 4; (c) Hanessian, S. Preparative Carbohydrate
Chemistry; Marcel Dekker: New York, 1997.
OMs
CO2Me
16
OBz
15
´
2. (a) Kocienski, P. J. Protecting Groups; Georg Thieme:
New York, 1994; (b) Meskens, F. A. J. Synthesis 1981,
501; (c) Schelhaas, M.; Waldmann, H. Angew. Chem., Int.
Ed. 1996, 35, 2056.
Ph
O
O
OH
OH
TBDPSO
17
TBDPSO
TBDPSO
OH
3. (a) Aravind, A.; Baskaran, S. Tetrahedron Lett. 2005, 46,
743–745, and references cited therein; (b) Aravind, A.;
Mohanty, S. K.; Pratap, T. V.; Baskaran, S. Tetrahedron
Lett. 2005, 46, 2965–2968; (c) Balakumar, V.; Aravind, A.;
Baskaran, S. Synlett 2004, 647–650.
4. Hanessian, S.; Staub, A. P. A. Tetrahedron Lett. 1973, 37,
3551–3554.
5. Deslongchamps, P.; Moreau, C.; Frehel, D.; Chenevert, R.
Can. J. Chem. 1975, 73, 1204–1211.
6. (a) Chidambaram, N.; Bhat, S.; Chandrasekaran, S.
J.Org. Chem. 1992, 57, 5013–5015; (b) Sato, K.; Igarashi,
T.; Yanagisawa, Y.; Kawauchi, N.; Hashimoto, H.;
Yoshimura, J. Chem. Lett. 1988, 1699–1702; (c) Ziegler,
F. E.; Tung, J. S. J.Org. Chem. 1991, 56, 6530; (d)
Wiegerinck, P. H. G.; Fluks, L.; Hammink, J. B.; Mulders,
S. J. E.; de Groot, F. M. H.; van Rozendaal, H. L. M.;
Scheeren, H. W. J. Org. Chem. 1996, 61, 7092; (e)
Hosokawa, T.; Imada, Y.; Murahashi, S. I. J. Chem.
Soc., Chem. Commun. 1983, 1245–1246.
18
OBz
Ph
O
O
OMs
OMs
OH
TBDPSO
19
OMs
20
OBz
Ph
O
O
OH
N3
N3 OMs
21
22
a Reaction time: 30–45 min.
b Isolated yield of the major isomer.
c In addition, the minor regioisomer was isolated in 9–13% yield.
7. Binkley, R. W.; Goewey, G. S.; Johnson, J. C. J. Org.
Chem. 1984, 49, 992–996.
8. Bhat, S.; Ramesh, A. R.; Chandrasekaran, S. Synlett 1995,
329.
9. Luzzio, F. A.; Bobb, R. A. Tetrahedron Lett. 1997, 38,
1733–1736.
10. Yongsheng, C.; Peng, G. W. Tetrahedron Lett. 2001, 42,
4955–4958.
To a solution of benzylidene acetal 1a (200 mg,
0.2397 mmol) in ethyl acetate (6 ml) was added a solu-
tion of KBrO3 (240 mg, 1.44 mmol) in water (3.5 ml) fol-
lowed by a solution of Na2S2O4 (250 mg, 1.44 mmol) in
water (3.5 ml) and the mixture stirred at room tempera-
ture for 45 min. After completion of the reaction, the
organic layer was separated, washed with sodium thio-
sulfate solution and the aqueous layer was extracted
with EtOAc. The combined organic layers were dried
over anhydrous sodium sulfate, concentrated under re-
duced pressure and purified by column chromatography
on silica gel using EtOAc–hexane, gradient elution, to
furnish pure compound 2a (179 mg, 86% yield) as a
11. Adinolfi, M.; Barone, G.; Guariniello, L.; Iadonisi, A.
Tetrahedron Lett. 1999, 40, 8439–8441.
26
12. Spectral data for selected compounds: Compound 2b: ½aꢁD
+16.6 (c 1, CHCl3); IR (CHCl3): 3514, 3031, 2939, 1721,
1601, 1451, 1343, 1263, 1174, 1093, 1069, 1025, 970, 921,
1
803, 710, 686, 521 cmꢀ1; H NMR [400 MHz, CDCl3] d:
7.99 (m, 4H), 7.52 (m, 2H), 7.38 (m, 4H), 5.80 (d,

1178
P. M. Senthilkumar et al. / Tetrahedron Letters 48 (2007) 1175–1178
J = 6.3 Hz, 2H), 4.94 (dd, J = 9.2, 3.7 Hz, 2H), 3.99 (dd,
5.23 (m, 1H), 4.10 (m, 2H), 3.39 (dd, J = 10.6, 4 Hz, 1H),
3.88 (dd, J = 9.7, 5.8 Hz, 1H), 2.88 (s, 3H); 1.80 (br s, 1H);
13C NMR [100 MHz, CDCl3] d: 165.8, 133.7, 129.8, 129.7,
128.9, 128.6, 128.5, 76.8, 71.6, 71.0, 96.6, 38.2. HRMS
(ESI) calcd for C12H15IO6SNa (M+Na)+: 436.9532.
J = 13.3, 3 Hz, 2H), 3.73 (dd, J = 13.3, 2.9 Hz, 2H), 3.56
(br s, 2H), 3.02 (s, 6H); 13C NMR [100 MHz, CDCl3] d:
165.8, 133.8, 129.9, 128.7, 128.6, 80.4, 69.8, 60.6, 38.6.
HRMS (ESI) calcd for C22H26O12S2Na (M+Na)+:
26
26
569.0763. Found: 569.0756. Compound 2d: ½aꢁD +56.6 (c
Found: 436.9531. Compound 14: ½aꢁD ꢀ6.8 (c 1, CHCl3);
1, CHCl3); IR (CHCl3): 3480, 2930, 2857, 1720, 1451,
1427, 1315, 1273, 1176, 1111, 1070, 1026, 772, 708, 687,
IR (CHCl3): 3451, 2928, 2093, 1716, 1601, 1584, 1492,
1450, 1384, 1315, 1265, 1177, 1096, 1069, 1025, 936, 755,
506 cmꢀ1
;
1H NMR [400 MHz, CDCl3] d: 8.03 (d,
707, 554, 499, 429 cmꢀ1; H NMR [400 MHz, CDCl3] d:
1
J = 7.1 Hz, 2H), 7.96 (d, J = 7.1, 2H), 7.67 (m, 2H), 7.58
(m, 4H), 7.42 (m, 5H), 7.34 (m, 2H) 7.1 (m, 3H), 5.96 (d,
J = 8 Hz, 1H), 5.71 (dd, J = 6.4, 3.1 Hz, 1H), 4.98 (m,
1H), 3.99 (m, 2H), 3.92 (m, 1H), 3.82 (m, 1H), 3.56 (m,
1H) 3.1 (s, 3H), 1.04 (s, 9H), 2.04 (br s, 2H); 13C NMR
[100 MHz, CDCl3] d: 166, 165, 135.8, 135.7, 133.6, 133.5,
132.0, 129.98, 129.92, 129.89, 129.39, 129.0, 128.5, 127.8,
127.7, 79.6, 72.5, 71.2, 69.4, 62.4, 61.0, 38.7, 27.0, 19.1.
HRMS (ESI) calcd for C37H42O10SSiNa (M+Na)+:
7.97 (m, 2H), 7.52 (m, 1H), 7.37 (t, J = 7.6 Hz, 2H), 4.62
(dd, J = 11.7, 4.6 Hz, 1H), 4.45 (dd, J = 11.5, 7.5 Hz, 1H),
3.80 (m, 2H), 3.43 (m, 2H), 2.44 (d, J = 6.1 Hz, 1H); 13C
NMR [100 MHz, CDCl3] d: 166.2, 133.5, 129.8, 129.1,
128.6, 69.9, 64.1, 61.9, 53.6. HRMS (ESI) calcd for
C11H12N6O3Na (M+Na)+: 299.0869. Found: 299.0868.
26
Compound 16: ½aꢁD +12.2 (c 1, CHCl3); IR (CHCl3):
3451, 2955, 1780, 1719, 1601, 1451, 1348, 1316, 1269, 1171,
1109, 1070, 1025, 971, 918, 805, 753, 710, 686, 525,
26
1
729.2166. Found: 729.2184. Compound 8: ½aꢁD +25.3 (c
449 cmꢀ1; H NMR [400 MHz, CDCl3] d: 8.02 (m, 2H),
1, CHCl3); IR (CHCl3): 3473, 1716, 1601, 1451, 1317,
7.59 (m, 1H), 7.37 (t, J = 7.6 Hz, 2H), 5.39 (dd, J = 6.7,
3.2 Hz, 1H), 4.97 (dd, J = 7.7, 3.7 Hz, 1H), 3.95 (dd,
J = 12.6, 3.8 Hz, 1H), 3.89 (dd, J = 12.6, 6.8 Hz, 1H), 3.63
(s, 3H), 3.62 (s, 3H), 3.56 (t, J = 7 Hz, 1H), 3.11 (s, 3H),
2.45 (t, J = 7.1 Hz, 1H); 13C NMR [100 MHz, CDCl3] d:
169.2, 169.0, 165.8, 133.6, 129.8, 129.0, 128.6, 82.5, 70.4,
61.4, 52.8, 52.7, 48.0, 38.7, 28.6; (ESI) C17H22O10S
1262, 1112, 1068, 1026, 972, 908, 709 cmꢀ1 1H NMR
;
[400 MHz, CDCl3] d: 8.1 (m, 4H), 7.52 (m, 2H), 7.46 (m,
4H), 5.49 (t, J = 10 Hz, 1H), 5.39 (dd, J = 3.6, 1.6 Hz,
1H), 4.92 (d, J = 1.3 Hz, 1H), 4.43 (dd, J = 10, 3.2 Hz,
1H), 3.9 (ddd, J = 10, 4, 2.4 Hz, 1H), 3.74 (m, 2H), 3.4 (s,
3H), 2.75 (br s, 1H), 2.56 (br s, 1H); 13C NMR [100 MHz,
CDCl3] d: 167.2, 166, 133.7, 133.5, 129.9, 129.2, 129.0,
128.6, 128.5, 98.5, 72.8, 70.4, 70.3, 68.5, 61.4, 55.4. HRMS
(ESI) calcd for C21H22O8Na (M+Na)+: 425.1212. Found:
26
(M+Na)+ 441. Compound 18: ½aꢁD +15.4 (c 1, CHCl3);
IR (CHCl3): 3411, 2930, 2856, 2360, 2341, 1718, 1471,
1450, 1314, 1268, 1177, 1069, 1040, 1026, 996, 822, 740,
26
1
425.1225. Compound 10a: ½aꢁD +22.8 (c 1, CHCl3); IR
699, 613, 503, 488 cmꢀ1; H NMR [400 MHz, CDCl3] d:
(CHCl3): 2930, 1718, 1450, 1427, 1314, 1269, 1104, 1068,
1026, 998, 907, 821, 758, 731, 698, 648, 611, 502 cmꢀ1; 1H
NMR [400 MHz, CDCl3] d: 8.09 (m, 2H), 7.73 (m, 8H),
7.52 (m, 1H), 7.42 (m, 14H), 5.57 (m, 1H), 4.23 (dd,
J = 9.1, 4.4 Hz, 2H), 4.08 (m, 1H), 3.75 (m, 2H), 2.29 (br s,
1H), 1.16 (s, 9H), 1.13 (s, 9H); 13C NMR [100 MHz,
CDCl3] d: 166.2, 136.3, 135.9, 135.9, 135.9, 133.9, 133.3,
133.2, 130.4, 130.2, 130.2, 130.2, 130.2, 130.2, 128.5, 128.1,
128.0, 75.8, 74.0, 63.7, 62.8, 27.2, 27.2, 19.7, 19.4. HRMS
(ESI) calcd for C43H50O5Si2Na (M+Na)+: 725.3095.
7.95 (m, 2H), 7.59 (m, 4H), 7.54 (m, 1H), 7.37 (m, 6H),
7.17 (m, 2H), 5.05 (m, 1H), 3.96 (m, 3H), 3.64 (m, 1H),
3.57 (m, 1H), 3.13 (br s, 1H), 2.78 (br s, 1H), 0.95 (s, 9H);
13C NMR [100 MHz, CDCl3] d: 166.2, 135.1, 132.9, 132.4,
132.3, 129.5, 129.4, 129.1, 128.0, 127.4, 127.3, 73.7, 70.3,
62.8, 62.4, 26.3, 18.7. HRMS (ESI) calcd for C27H32O5-
SiNa (M+Na)+: 487.1917. Found: 487.1917. Compound
26
20: ½aꢁD +1.5 (c 1, CHCl3); IR (CHCl3): 2342, 1723, 1360,
1272, 1176, 1112, 922, 828, 773, 742, 708, 505 cmꢀ1 1H
;
NMR [400 MHz, CDCl3] d: 7.97 (d, J = 7.6 Hz, 2H), 7.60
(m, 5H), 7.35 (m, 8H), 5.03 (m, 1H), 4.60 (dd, J = 12.2,
2.7 Hz, 1H), 4.50 (dd, J = 6.4, 2.8 Hz, 1H), 3.92 (m, 1H),
3.77 (m, 2H), 3.28 (s, 3H), 2.2 (s, 1H), 1.016 (s, 9H); 13C
NMR [100 MHz, CDCl3] d: 166.18, 135.60, 135.59,
133.37, 132.50, 132.45, 130.09, 129.77, 129.39, 128.53,
127.94, 79.37, 70.47, 63.38, 63.18, 38.73, 26.84, 19.21.
HRMS (ESI) calcd for C28H34O7SSiNa (M+Na)+:
26
Found: 725.3089. Compound 10b: ½aꢁD +3.7 (c 1, CHCl3);
IR (CHCl3): 3410, 2953, 2928, 2884, 2856, 1720, 1471,
1463, 1315, 1271, 1253, 1097, 1068, 1026, 1003, 938, 830,
811, 775, 734, 708, 686, 669, 461 cmꢀ1
;
1H NMR
[400 MHz, CDCl3] d: 8.01 (m, 2H), 7.50 (m, 1H), 7.38
(m, 2H), 5.16 (dd, J = 9.8, 4.3 Hz, 1H), 4.12 (dd, J = 9.8,
4.3 Hz, 1H), 3.99 (dd, J = 11.2, 4.2 Hz, 1H), 3.88 (dd,
J = 11.2, 4.3 Hz, 1H), 3.70 (dd, J = 13.4, 4 Hz, 1H), 3.67
(dd, J = 13.4, 4.1 Hz, 1H), 2.4 (br s, 1H), 0.89 (s, 9H), 0.84
(s, 9H), 0.10 (s, 6H), ꢀ0.0073 (s, 6H); 13C NMR
[100 MHz, CDCl3] d: 167.5, 134.7, 131.8, 131.4, 130.0,
76.6, 73.2, 65.1, 62.7, 27.5, 27.4, 19.9, 19.7, ꢀ2.8, ꢀ3.170,
ꢀ3.72, ꢀ3.76. HRMS (ESI) calcd for C23H42O5Si2Na
(M+Na)+: 477.2469. Found: 477.2454. Compound 12:
26
565.1692. Found: 565.1689. Compound 22: ½aꢁD ꢀ2.3 (c
1, CHCl3); IR (CHCl3): 3509, 3034, 2937, 2869, 2347,
2101, 1719, 1472, 1457, 1397, 1357, 1293, 1219, 1176, 1126,
1093, 1064, 1001, 962, 899, 869, 833, 756, 699,
660, 525 cmꢀ1 1H NMR [400 MHz, CDCl3] d: 8.07
;
(m, 2H), 7.63 (m, 1H), 7.49 (m, 2H), 5.46 (m, 1H), 5.02
(m, 1H), 4.03 (dd, J = 12.9, 3.8 Hz, 1H), 3.8 (dd, J = 5.5,
12.9 Hz, 1H), 3.74 (m, 2H), 3.1 (s, 3H), 2.0 (s, 1H); 13C
NMR [100 MHz, CDCl3] d: 165.6, 133.9, 129.7,
128.7, 128.6, 80.2, 70.6, 61.3, 50.4, 38.8. HRMS (ESI)
calcd for C12H15N3O6SNa (M+Na)+: 352.0579. Found:
352.0574.
26
½aꢁD ꢀ3.8 (c 1, CHCl3); IR (CHCl3): 3514, 2938, 1719,
1601, 1584, 1451, 1357, 1268, 1173, 1116, 1070, 1025, 967,
918, 848, 752, 709, 667, 521, 460 cmꢀ1
;
1H NMR
[400 MHz, CDCl3] d: 7.97 (t, J = 7.3 Hz, 2H), 7.49 (d,
J = 7.4 Hz, 1H), 7.36 (t, J = 7.6 Hz, 2H), 5.41 (m, 1H),