An investigation of the behaviour of α,β-unsaturated sulfoxides in the presence of trimethylsilyl iodide

Article abstract of DOI:10.1016/S0040-4020(02)01365-0

A mild, efficient and seemingly general method for converting α,β-unsaturated sulfoxides into carbonyl compounds by means of trimethylsilyl iodide (TMSI) is described. Experiments on different substrates and trimethylsilyl halides lead to the conclusion that the oxidation state of the sulfur atom, on one hand, and halogen kind in TMSX on the other, assume a determining role in the progression of the reaction. The ease of experimental procedure, the possibility of ¹H NMR monitoring, and good yields of final products constitute advantages of the TMSI-promoted conversion of α,β-unsaturated sulfoxides into carbonyl compounds.

Full text of DOI:10.1016/S0040-4020(02)01365-0

Tetrahedron 58 (2002) 10145–10150
An investigation of the behaviour of a,b-unsaturated sulfoxides in
the presence of trimethylsilyl iodide
*
Maria C. Aversa, Anna Barattucci, Paola Bonaccorsi and Placido Giannetto
*
`
Dipartimento di Chimica organica e biologica, Universita degli Studi di Messina, Salita Sperone 31 (vill. S. Agata), 98166 Messina, Italy
Received 30 July 2002; revised 1 October 2002; accepted 24 October 2002
Abstract—A mild, efficient and seemingly general method for converting a,b-unsaturated sulfoxides into carbonyl compounds by means of
trimethylsilyl iodide (TMSI) is described. Experiments on different substrates and trimethylsilyl halides lead to the conclusion that the
oxidation state of the sulfur atom, on one hand, and halogen kind in TMSX on the other, assume a determining role in the progression of the
reaction. The ease of experimental procedure, the possibility of 1H NMR monitoring, and good yields of final products constitute advantages
of the TMSI-promoted conversion of a,b-unsaturated sulfoxides into carbonyl compounds. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
We now report extensions of our previous observation, for
supporting the generality and efficiency of this procedure,
even in the presence of sterically and electronically different
substituents directly linked to the sulfinyl vinyl moiety.
Some results support the reaction mechanism that we
discuss below, others define the limits of this procedure, like
for instance the use of trimethylsilyl halides different from
iodide.
Trimethylsilyl iodide (TMSI) is a versatile synthetic reagent
which interacts very readily with organic molecules
containing oxygen and promotes the cleavage of carbon–
oxygen bonds of compounds such as ethers, esters, ketals,
acetals, lactones, carbamates, and epoxides.1 It has also
proved useful for the synthesis of alkyl iodides from
alcohols,2 for the silylation of carbonyl compounds,3 allylic
carbanions,4 and for reducing azides to amines,5 sulfoxides
to sulfides, and sulfonyl halides to the corresponding
disulfides. Recently, we have described a mild and efficient
method for converting a,b-unsaturated sulfoxides into
carbonyl compounds by means of TMSI.6 The reaction
starts with prompt formation of iodine, which indicates a
redox process, and generally, within a few hours, the
starting vinyl sulfoxides are transformed into precursors of
carbonyl compounds, and disulfides, as shown in Eq. (1).
2. Results and discussion
Treatment of a,b-unsaturated sulfoxides with TMSI at room
temperature in chloroform gives the corresponding carbonyl
compounds. Substrates, final products, reaction times, and
yields of the investigated reactions with TMSI are shown in
Table 1 (entries 1, 4–14) together with experiments
performed on phenyl vinyl sulfoxide (1) with trimethylsilyl
bromide (TMSBr) (entry 2) and trimethylsilyl chloride
(TMSCl) (entry 3). The substrates 2–4 come from LiAlH4
reduction of esters obtained as enantiopure products of
stereocontrolled Diels–Alder cycloadditions.12,23
2CH2vCH–SðOÞR þ 2TMSI
¼ 2CH2vCH–OTMS þ RSSR þ I2
ð1Þ
All the reactions ended within 6 h, apart from the one
involving the substrate 5 (entry 7). Entries 1 and 6 refer to
reactions performed with TMSI in CDCl3, inside a NMR
tube, monitored by 1H NMR experiments, and the
desulfurated products were identified in situ as acetaldehyde
(6) and (S)-2,3-dihydro-2-hydroxymethylpyran-4-one (7),
together with disulfides 8 and 9, respectively, (see footnote
b in Table 1). Also the reactions of phenyl vinyl sulfoxide
(1) with TMSBr and TMSCl (entries 2 and 3) were
performed in NMR tube, and in both cases the final
products still contained the sulfur atom. TMSBr promoted
reduction of the sulfinyl moiety followed by electrophilic
The methodology offers some advantages: (i) TMSI-
promoted reactions can be performed in NMR tubes and
followed by 1H NMR spectroscopy; (ii) yields of final
products are generally good; (iii) the C–S cleavage in the
a,b-unsaturated sulfoxides leads to functionalization of the
substrates with a carbonyl group which can be easily
involved into numerous synthetic transformations.
Keywords: carbonyl compounds; cleavage reactions; desulfurisation;
sulfoxides.
*
Corresponding authors. Tel.: þ39-090-6765165; fax: þ39-090-393895;
e-mail: aversa@unime.it; annab@isengard.unime.it
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)01365-0

10146
M. C. Aversa et al. / Tetrahedron 58 (2002) 10145–10150
Table 1. TMSX-promoted conversion of a,b-unsaturated sulfoxides at RT in chloroform
Entry
1
Substratea
Ref. for
substrate
Reagent
TMSI
Productsb
Ref. for
products
Time
(h)
Yield
(%)
Com-
mercial
Com-
mercial
4
.95c
.95c
40c
2
3
Com-
mercial
TMSBr
TMSCl
7
4
Com-
mercial
Com-
mercial
0.2
4
5
6
6
TMSI
TMSI
TMSI
6,8
1
1
4
70
80
d
9
7
8
6,10
6,12
TMSI
TMSI
6,11
144
50þ23
6,13
15
3
50
9
14
16
TMSI
TMSI
0.3
63þ32
10
Com-
mercial
5
60
11
17
TMSIe
17
1.5
50
12
13
6,18
TMSI
TMSI
Com-
mercial
6
5
70
10,19
Com-
mercial
.95

M. C. Aversa et al. / Tetrahedron 58 (2002) 10145–10150
10147
Table 1 (continued)
Entry
Substratea
Ref. for
substrate
Reagent
TMSI
Productsb
Ref. for
products
Time
(h)
Yield
(%)
14
6,10
6,11
1.5
55þ27
a
b
Disulfides 8 (entries 1, 12), 9 (entries 4–6, 8, 9, 13, 14),20 29 (entry 7),21 and 30 (entry 10)22 were also obtained.
c
d
e
The experiment was performed on a NMR scale and the yield estimated by integration of significant proton resonances.
The yield is not reported because of unstability of 7.9
The reaction required a 2.5:1 molar ratio of TMSI/substrate to be completed (see Section 4).
addition of bromine to the double bond, whereas TMSCl
followed by dehydration, can be ascribed to intramolecular
hydrogen bonding which stabilizes the reaction product 17
as depicted in A.
was unable to reduce the sulfinyl group, a predictable result
on the basis of the redox potential of chlorine/chloride
couple, and the HCl addition to the vinyl function was the
unique reaction observed in this case. A comparison of the
results reported in entries 1–3 clearly proves that TMSI was
uniquely effective for promoting conversion of vinyl
sulfoxides into carbonyl compounds.
The mechanism we suggest for explaining the outcome of
these reactions with TMSI is depicted in Scheme 1.
Formation of a strong oxygen–silicon bond1 is followed
by reduction of the sulfur function and oxidation of iodide to
iodine, which precipitates in chloroform as a brown red
solid. Trimethylsilyloxy anion attacks the unsaturated
carbon linked to the sulfur function, which leaves the
substrate, allowing the formation of trimethyl(vinyloxy)-
silane 10. Finally, water converts vinyl ether 10 into
carbonyl compound.
In line with previous results, a,b-unsaturated aldehydes 14
and 15 were the final desulfurated products of TMSI-
promoted reaction on substrate 16 which lost a stereogenic
carbon atom by dehydration (entry 9 in Table 1).
In the substrate 18, S(O) is located between two unsatura-
tions which show a different electronic nature. We assume
that the formation of 19 in the reaction of 18 with TMSI
(entry 10 in Table 1) is due to the attack of the
trimethylsilyloxy anion onto the more electrophilic unsatu-
rated carbon, the one linked to the nitrogen atom, in the
cationic species analogous of 20 in Scheme 1.
Cleavage of the O–Me bond by means of TMSI and
subsequent dehydration to form a double bond conjugated
with the carbonyl function are proposed for substrates 2, 4,
and 11 which were transformed into a,b-unsaturated
ketones 12, 7, and 13 respectively (see entries 4, 6, and 8
in Table 1). This hypothesis is supported by a comparison of
the results observed in the experiments involving the
starting products 2 and 3 (entries 4 and 5): the hydro-
xymethyl a,b-unsaturated ketone 12, in one case, and the
triol 17, in the other, have been obtained in the same
reaction times and comparable yields. For the conversion of
3 in 17, the TMSI-promoted cleavage of O–Me bond, not
The reaction of 21 with TMSI afforded the desulfurated
16-azasteroid derivative 22 (entry 11 in Table 1). The
attribution of its structure is based mainly on NMR
measurements, such as APT and homodecoupling (see
Section 4) in comparison with corresponding experiments
performed on the precursor 21.17 Noteworthy, no conver-
sion of a,b-unsaturated sulfoxide moiety into a carbonyl
function was observed when compound 21 underwent the
Scheme 1.

10148
M. C. Aversa et al. / Tetrahedron 58 (2002) 10145–10150
TMSI treatment, and the cleavage of the C–S bond was
followed by reductive migration of the double bond from
the 9(11) to the 8 position. The reaction required a 1:2.5
molar ratio of substrate/TMSI to be completed, and no
formation of disulfide 9 was observed. These results lead us
to believe that the mechanistic outcome of this reaction
differs from the one proposed for the other a,b-unsaturated
sulfoxides investigated (entries 1, 4–10, 12–14) possibly
because of high conformational rigidity of the steroidal
skeleton and consequent difficulty of TMSO2 in approach-
ing the electrophilic unsaturated C-11. This significant
result holds a prospect of further investigation in a very near
future.
2.19 mmol) was added in small subsequent amounts to a
solution of (3R,4R,RS)-1-[(1S)-isoborneol-10-sulfinyl]-3-
methoxy-4-methoxycarbonylcyclohexene
(404 mg,
1.09 mmol)23a in anhydrous Et2O (30 ml) at 2788C, under
stirring and argon atmosphere. The resulting mixture was
allowed to reach room temperature, and the reaction
monitored by TLC (eluant light petroleum/EtOAc 50:50)
until the starting material had totally disappeared (1 h). The
reaction was then quenched by careful addition of H2O
(15 ml). The organic layer was separated and the water
phase extracted with Et2O (2£20 ml) and EtOAc (2£20 ml).
The combined organic layers were dried over anhydrous
Na2SO4 and concentrated in vacuo to afford 365 mg (98%
1
yield) of the expected alcohol 2 as a light yellow oil; H
NMR: d 6.69 (dd, 1H, J2,3¼4.1 Hz, J2,6¼1.8 Hz, H-2), 4.12
0
0
0
(dd, 1H, J2 ,3 ¼7.8 and 3.6 Hz, H-2 ), 4.05 (t, 1H,
J3,4¼4.1 Hz, H-3), 3.79 (m, 2H, CH2OH), 3.48 (s, 3H,
3. Conclusion
0
0
OMe), 3.14 and 2.42 (AB system, 2H, J10 A,10 B¼13.0 Hz,
H2-100), 2.3–1.1 (m, 12H, H02-30,5,50,6,60, H-4,40), 1.08 (s,
3H, H3-80), 0.83 (s, 3H, H3-9 ); 13C NMR: d 146.39 (C-1),
126.92 (C-2), 77.00 (C-20), 75.44 (C-3), 64.20 (CH2OH),
57.25 (OMe), 53.47 (C-100), 51.42 (C-10), 48.27 (C-70),
45.09 (C-40), 40.04 (C-4), 38.39 (C-30), 30.88 and 27.13
(C-500,600), 22.33 (C-6), 21.12 (C-5), 20.52 and 19.88
(C-8 ,9 ); MS/FAB: m/z (%) 343 (Mþ1, 30), 155 (43), 138
(56), 137 (100), 107 (43), 89 (38), 77 (36); IR: nmax 3415
(OH) cm21; Anal. calcd for C18H30O4S: C, 63.12; H, 8.83;
Found: C, 62.84; H, 8.72.
In conclusion, we have demonstrated the validity of TMSI
methodology for the cleavage of C–S bond in a,b-
unsaturated sulfoxides, which in almost all the performed
experiments resulted in the conversion of the sulfinyl moiety
into a carbonyl, providing useful synthetic possibilities.
Oxidation state of the sulfur atom, on one hand, and halogen
kind in TMSX, on the other, assume a determining role in
the progression of the reaction which can be performed on
enantiopure substrates without any racemization of stereo-
genic centres. The ease of experimental procedure and the
possibility of 1H NMR monitoring constitute further
advantages of this reaction.
4.1.2. (3R,4S,5R,RS)-4,5-Dihydroxymethyl-1-[(1S)-iso-
borneol-10-sulfinyl]-3-methoxycyclohexene (3). LiAlH4
(26.6 mg, 0.70 mmol) was added in small subsequent
amounts to a solution of (3R,4R,5R,RS)-4,5-dimethoxy-
carbonyl-1-[(1S)-isoborneol-10-sulfinyl]-3-methoxycyclo-
hexene (100 mg, 0.23 mmol)12 in anhydrous Et2O (10 ml) at
2788C, under stirring and argon atmosphere. The resulting
mixture was allowed to reach the room temperature, and the
reaction monitored by TLC (eluant EtOAc/light petroleum
80:20) until the starting material had totally disappeared
(18 h). The reaction was then quenched by careful addition
of H2O (15 ml). The organic layer was separated and the
water phase extracted with Et2O (2£20 ml) and EtOAc
(2£20 ml). The combined organic layers were dried over
anhydrous Na2SO4 and concentrated in vacuo to afford the
crude diol 3 which was purified by column chromatography
first eluting with EtOAc/light petroleum 50:50 and gradu-
ally increasing the polarity of the eluant up to 90% EtOAc.
The pure 3 was obtained (71% yield) as a light yellow oil;
4. Experimental
4.1. General
Solvents were purified according to standard procedures.
Petroleum ether used refers to the fraction boiling at 30–
508C. All reactions were monitored by TLC on com-
mercially available precoated plates (Aldrich silica gel 60 F
254) and the products were visualized with vanillin [1 g
dissolved in MeOH (60 ml) and conc. H2SO4 (0.6 ml)].
Silica gel used for column chromatography was Aldrich 60.
Melting points were recorded on a microscopic apparatus
and are uncorrected. Optical rotations were measured for
CHCl3 solutions on a Jasco P-1030 polarimeter (concen-
1
trations c are in g/100 ml). H and 13C NMR spectra were
recorded on a Varian Mercury 300 spectrometer at 300 and
75 MHz respectively in CDCl3 solutions with SiMe4 as
internal standard: J values are given in Hz; the attributions
are supported by Attached Proton Test (APT) and homo-
decou0pling experiments; proton and carbon nuclei, marked
with ( ), pertain to the isoborneol moiety in compounds 2–4
and phenyl group in compounds 22 and 23. Mass spectra
were measured by Electron Impact (EI, 70 eV) or Fast Atom
Bombardment (FAB, m-nitrobenzyl alcohol as matrix) with
a Finnigan MAT 90 instrument. IR spectra were recorded in
CHCl3 solutions on a Nicolet 410 D FTIR spectrometer. The
analytical/spectral data collected for products 6–9, 12–15,
19, 22, 24–30 were consistent with those reported in the
literature (see references in Table 1).
1H NMR: d 6.48 (m, 1H, J2,3¼4.2 Hz, H-2), 4.15 (dd, 1H,
0
0
0
J2 ,3 ¼7.7 and 2.6 Hz, H-2 ), 4.09 (dd, 1H, J3,4¼8.3 Hz,
H-3), 3.9–3.6 (m, 4H, CH2OH), 3.49 (s, 3H, OMe), 3.27
and 2.34 (AB system, 2H, J10 A,10 B¼13.0 Hz, H2-100), 2.5–
1.2 (m, 11H, H2-30,50,6,60, H-4,40,5), 1.09 (s, 3H, H3-80),
0.83 (s, 3H, H3-90); 13C NMR: d 143.43 (C-1), 130.10 (C-2),
78.42 (C-3), 76.97 (C-20), 63.97 (4-CH2OH), 57.86
(5-CH2OH), 57.14 (OMe), 53.00 (C-100), 51.32 (C-10),
48.24 (C-70), 44.98 (C-40), 41.14 (C-4), 38.31 (C-30), 37.57
(C-5), 30.74 0and 27.04 (C-50,60), 21.15 (C-6), 20.44 and
19.83 (C-80,9 ); IR: nmax 3432 (OH) cm21; Anal. calcd for
C19H32O5S: C, 61.26; H, 8.66; Found: C, 61.30; H, 8.72.
0
0
4.1.3. (2R,6S,RS)-5,6-Dihydro-6-hydroxymethyl-4-[(1S)-
isoborneol-10-sulfinyl]-2-methoxy-2H-pyran (4). The
4.1.1. (3R,4S,RS)-4-Hydroxymethyl-1-[(1S)-isoborneol-
10-sulfinyl]-3-methoxycyclohexene (2). LiAlH4 (83 mg,

M. C. Aversa et al. / Tetrahedron 58 (2002) 10145–10150
10149
alcohol
4
was obtained by LiAlH4 reduction of
calcd for C18H19NO3: C, 72.71; H, 6.44; Found: C, 72.59;
H, 6.37.
(2R,6S,RS)-5,6-dihydro-6-ethoxycarbonyl-4-[(1S)-isoborneol-
10-sulfinyl]-2-methoxy-2H-pyran23b following the pro-
cedure above reported for the preparation of 2. The
reduction appeared complete after 5 h. The crude product
4, purified by column chromatography eluting with CHCl3/
EtOAc 50:50, was obtained in 79% yield as a light yellow
oil, [a]2D2¼23.5 (c 1.07); 1H NMR: d 6.33 (dt, 1H,
J2,3¼J3,5B¼1.9 Hz, J3,5A¼1.7 Hz, H-3), 5.22 (dt, 1H,
J2,5A¼J2,5B¼2.2 Hz, H-2), 4.1–3.7 (m, 4H, H-20,6,
CH2OH), 3.56 (s, 3H, OMe), 3.36 and 2.32 (AB system,
2H, J10 A,10 B¼13.0 Hz, H2-100), 2.52 (AB dddd, 1H,
J5 A,5B¼17.0 Hz, J5 A,6¼4.3 Hz, HA-5), 2.37 (AB ddt, 1H,
J5B,6¼8.1 Hz, HB-5), 2.3–1.1 (m, 7H, H2-30,50,60, H-40),
1.07 (s, 3H, H3-80), 0.81 (s, 3H, H3-90); 13C NMR:0d 145.01
(C-4), 128.70 (C-3), 97.45 (C-2), 0 76.90 (C-2 ), 64.94
(CH2OH), 56.41 (OMe), 53.06 (C-10 ), 51.34 (C-10), 48.33
(C-70), 44.99 (C-40), 38.40 (C-30), 30.74 and 27.08 (C-50,60),
21.04 (C-5), 20.46 and 19.85 (C-80,90); IR: nmax 3400
(OH) cm21; Anal. calcd for C17H28O5S: C, 59.27; H, 8.19;
Found: C, 59.45; H, 8.35.
4.2.3. (3aS,11aS)-7-Methoxy-2,3,3a,4,5,10,11,11a-octa-
hydro-2-phenylnaphth[2,1-e]isoindole-1,3(1H)-dione
(22). TMSI (97%, 0.40 mmol) was added to a solution of 21
(90 mg, 0.16 mmol) in CHCl3 (1.5 ml) under argon
atmosphere and stirring. The reaction, monitored by TLC,
appeared complete after 90 min. Then MeOH (5 ml) was
added and the stirring maintained for further 30 min. After
evaporation of the solvent under reduced pressure, purifi-
cation of the crude product by column chromatography with
light petroleum/EtOAc 95:5 as eluant afforded 22, low
melting solid, 29 mg, 50% yield, [a]2D4¼þ32.4 (c 3.26); 1H
NMR: d 7.5–6.7 (m, 5H, H-20,30,40,50,60), 3.80 (s, 3H, OMe),
0
0
3.69 (d, 1H, J3a,11a¼8.5 Hz, H-3a), 3.33 (dt, 1H, J11a,11A
¼
J11a,11B¼5.3 Hz, H-11a), 2.9–2.3 (m, 7H, H2-4,5,10, HA-
11), 1.94 (m, 1H, HB-11); 13C NMR: d 178.18 and 175.50
(C-1,3), 158.72 (C-7), 137.41 (C-5a), 131.91 (C-10), 131.24
and 1028.31 0 (C-3b,9b), 129.04, 128.43, and 126.38
(C-20,3 ,40,50,6 ), 124.23 (C-9a), 123.58 (C-9), 113.52
(C-6), 111.08 (C-8), 55.28 (OMe), 45.72 (C-3a), 40.07
(C-11a), 28.50, 27.33, 21.93, and 21.75 (C-4,5,10,11);
MS/EI: m/z (%) 359 (M, 100), 213 (11), 212 (62), 211 (16),
197 (11), 165 (10); Anal. calcd for C23H21NO3: C, 76.86; H,
5.89; Found: C, 76.79; H, 5.90.
4.2. General procedure for the TMSI-promoted
conversion of a,b-unsaturated sulfoxides into carbonyl
compounds
To a solution of a,b-unsaturated sulfoxide (0.53 mmol) in
anhydrous CHCl3 (3 ml), TMSI (97%, 0.64 mmol) was
added at RT. The reaction was monitored by TLC. After
disappearance of the starting material, MeOH (30 ml) was
added and the reaction mixture stirred for 0.5 h, concen-
trated under reduced pressure, and column chromato-
graphed eluting with light petroleum/EtOAc mixture
where the EtOAc percentage was gradually increased
from 10 up to 80%. The disulfide was eluted first in all
cases, followed by the carbonyl compounds.
4.3. General procedure for the reaction of a,b-
unsaturated sulfoxides with TMSBr and TMSCl
To a solution of a,b-unsaturated sulfoxide (0.13 mmol) in
anhydrous CDCl3 (0.7 ml), TMSBr 97% (0.16 mmol) [or
TMSCl .99% (0.16 mmol)] was added at RT. The reaction
was monitored and the products identified in situ by H
NMR.
1
4.2.1. (3S,4S,5R)-4,5-Dihydroxymethyl-3-hydroxycyclo-
hexanone (17). Oil, [a]2D0¼þ18.5 (c 0.32); 1H NMR: d 4.45
(broad s, 1H, H-3), 3.98 (AB ddd, 1H, Jgem¼8.7 Hz,
Jvic¼5.3 Hz, Jlong-range¼1.8 Hz, 5-CHAHBOH), 3.80 (AB d,
1H, 5-CHAHBOH), 3.76 (AB dd, 1H, Jgem¼11.4 Hz,
Jvic¼7.3 Hz, 4-CHAHBOH), 3.69 (AB dd, 1H, Jvic¼7.2 Hz,
4-CHAHBOH), 2.71 (AB dd, 1H, J2 A,2B¼17.6 Hz,
J2 A,3¼3.3 Hz, HA-2), 2.6–2.4 (m, 4H, H-4,5, H2-6), 2.41
(AB dd, 1H, J2B,3¼2.1 Hz, HB-2); 13C NMR: d 209.56
(C-1), 75.55 (C-3), 71.91 (5-CH2OH), 61.93 (4-CH2OH),
50.67 (C-4), 49.07 and 48.86 (C-2,6), 35.81 (C-5); IR: nmax
Acknowledgements
This work was carried out under the auspices of the national
project ‘Stereoselezione in sintesi organica, metodologie
ed applicazioni’ supported by MIUR (Ministero
`
dell’Istruzione, dell’Universita e della Ricerca) Rome,
Italy. The work was also supported by the University of
Messina (funds for selected topics of interdisciplinary
research). We thank Professor Patrick Rollin, University
´
of Orleans, France, for the generous gift of a sample of 2-
[(Z)-2-phenylethenyl]sulfinylbenzothiazole.
3452 (OH), 1716 (CO) cm21
.
4.2.2. (3aR,5aS,9aS,9bS)-Octahydro-2-phenyl-1H-benz-
[e]isoindole-1,3,5(2H,4H)-trione (23). White cry0stals, mp
0
0
0
0
1
233–2358C; H NMR: d 7.5–7.2 (m, 5H, H-2 ,3 ,4 ,5 ,6 ),
References
3.49 (ddd, 1H, J3a,4A¼2.2 Hz, J3a,4B¼8.0 Hz, J3a,9b
¼
9.8 Hz, H-3a), 3.29 (dd, 1H, J9a,9b¼5.7 Hz, H-9b), 2.98
(AB dd, 1H, J4 A,4B¼16.2 Hz, HA-4), 2.79 (AB dd, 1H, HB-
4), 2.3–1.2 (m, 10H, H2-6,7,8,9, H-5a,9a); 13C NMR: 0 d
208.11 (C-5), 177.06 and 175.904 (C-1,3)0, 131.52 (C-1 ),
129.20, 128.82, and 126.37 (C-2 ,30,40,50,6 ), 49.11 (C-5a),
42.88 (C-9b), 38.85 (C-3a), 38.19 (C-9a), 37.03 (C-4),
29.05, 28.25, 25.95, and 25.29 (C-6,7,8,9); MS/EI: m/z (%)
297 (M, 100), 189 (10), 188 (73), 187 (10), 174 (10), 135
(22), 77 (10); IR: nmax 1715 (CO), 1500, 1384 cm21; Anal.
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