Condensation products of mono-and dibromo-substituted methyl vinyl sulfones with CH-acids enolates

Article abstract of DOI:10.1007/s10593-008-0058-9

Bromomethyl (E)-2-phenylethenyl and bromomethyl (Z)-1-bromo-2-phenylethenyl sulfones undergo condensation with enolates generated from malononitrile, dimethyl malonate, methyl and ethyl acetoacetate using NaH in THF to give tetrahydrothiophene S,S-dioxide

Full text of DOI:10.1007/s10593-008-0058-9

Chemistry of Heterocyclic Compounds, Vol. 44, No. 4, 2008
CONDENSATION PRODUCTS OF MONO-
AND DIBROMO-SUBSTITUTED METHYL VINYL
SULFONES WITH CH-ACIDS ENOLATES
V. A. Vasin1, I. Yu. Bolusheva1, and V. V. Razin2
Bromomethyl (E)-2-phenylethenyl and bromomethyl (Z)-1-bromo-2-phenylethenyl sulfones undergo
condensation with enolates generated from malononitrile, dimethyl malonate, methyl and ethyl
acetoacetate using NaH in THF to give tetrahydrothiophene S,S-dioxides. Methyl (E)-1-bromo-
2-phenylethenyl and methyl (E)-2-bromo-2-phenylethenyl sulfones react with sodium malononitrile to
give 2-[2-(methylsulfonyl)-1-phenylethylidene]malononitrile. The bromomethyl-(E)-2-bromo-2-phenyl
ethenyl sulfone reacts with sodium malononitrile to give 2-[2-(bromomethylsulfonyl)-1-
phenylethylidene]malononitrile exclusively.
Keywords: CH-acids enolates, tetrahydrothiophene-S,S-dioxide, 2-phenylethenyl sulfones, ethylidene-
malononitrile, heterocyclization, Michael reaction, Ramberg-Bäcklund reaction.
It is known [1, 2] that bromomethyl vinyl sulfones and, in particular, the sulfone 1a undergo a Michael
induced Ramberg-Bäcklund (MIRB) addition reaction when treated with sodium alcoholate to give alkyl allyl
ethers. Benzyl α-bromovinyl sulfone reacts with different nucleophiles by a similar scheme to give allyl
derivatives [3]. As members of the series of α-bromovinyl bromomethyl and β-bromovinyl bromomethyl
sulfones the dibromosulfones 2a and 3a also react via an MIRB reaction with sodium methylate, presumably
through a bromomethyl ethynyl sulfone stage to form a vinyl phenyl ketone dimethyl ketal in both cases [2]. It is
also known that some α-bromovinyl sulfones unable to take part in the Ramberg-Bäcklund reaction cyclize to
sulfonyl-substituted aziridine derivatives when treated with primary amines in DMSO [4]. Similarly, several
α-chlorovinyl sulfones not able to undergo the Ramberg-Bäcklund reaction undergo Michael induced addition
cyclization to give sulfonyl-substituted dihydrofuran and cyclopropane derivatives when treated with
ethylacetoacetate or diethyl malonate enolates [5].
The examples given point to a variety of reactions of halo-substituted methyl vinyl sulfones in Michael
induced addition reactions and open up a short route to the formation of acyclic, cyclic, and heterocyclic
structures difficult to prepare by other methods.
In this work we have studied the reactions of mono- and dibromo-substituted methyl vinyl sulfones with
CH-acids enolates with a view to determining the effect of the position and number of bromine atoms on the
_______
Dedicated to Professor A. A. Potekhin's memory.
__________________________________________________________________________________________
1N. P. Ogarev Mordovian State University, Saransk 430000, Russia; e-mail: vasin@mrsu.ru.
2St. Petersburg State University, St. Petersburg 198504, Russia; e-mail: vvrazin@mail.ru. Translated from
Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 539-551, April, 2008. Original article submitted October
16, 2007.
0009-3122/08/4404-0419©2008 Springer Science+Business Media, Inc.
419

420

TABLE 2. Mass Spectra of the Compounds Synthesized
Com-
m/z (I, %)
pound
2b
262 (12.9)/260 (12.9) [M]+•, 183 (9)/182 (79)/181 (24)/180 (81), 171 (7.2)/169 (7.7),
102 (100), 90 (10), 89 (9.7), 76 (19), 75 (12), 63 (12)
7
326 (3)/324 (3) [M]+•, 184 (98)/182 (100), 104 (36)/103 (71)/102 (25), 77 (60), 51 (43)
9b
248 (1.6)/246 (29.6) [M]+•, 181 (8), 169 (10), 168 (84), 167 (40.5), 142 (10), 141 (19),
140 (100), 127 (7), 114 (10), 113 (13), 103 (8), 102 (5), 79 (54), 78 (5), 77(21), 65 (4),
64 (7), 63 (12), 51 (23)
12
200 (0.3)/198 (5) [M]+•, 106 (7)/105 (100), 91 (9), 79 (2.7)/78 (3.5)/77 (34), 63 (2.7),
51 (13)
realization of one or the other possible routes for their reaction. We have chosen the bromomethyl vinyl sulfone
1a and bromomethyl bromovinyl sulfones 2a and 3a mentioned above together with the methyl bromovinyl
sulfones 2b and 3b as the subject of our investigation (Tables 1-3).
–
B
XCH2SO2Br
Ph
X
SO2
HBr
–
hν
Ph
Br
4a,b
H
Ph
Br
Ph
–
H
Ph
H
Br
Br2
B
Br
–
HBr
XCH2SO2
XCH2SO2
XCH2SO2
H
H
1a,b
5a,b
2a,b
Br
Ph
H
XCH2SO2Br
Ph
XCH2SO2
hν
3a,b
1–5 a Х = Br, b X = H
The starting materials 2a,b were prepared from the styrene photoadducts 4a,b respectively with
bromomethane- and methanesulfobromides. To do this the adducts 4a,b were treated with an aqueous dioxane
solution of Na2CO3 at 20ºC giving initially the sulfones 1a,b which were treated with bromine in CCl4 at 20ºC to
give the dibromides 5a,b. The dibromides 5a and 5b were then dehydrobrominated by heating in aqueous
dioxane Na2CO3 solution at 50ºC to give the sulfones 2a and 2b respectively. Compounds 3a and 3b were
prepared by the photochemical addition of bromomethane- and methanesulfobromide to phenylacetylene.
Detailed methods for the synthesis and proof of the structure of sulfones 1a-3a have been given by us in
[2]. The sulfones 1b [2] and 3b [6] were identified from the constants and spectroscopic parameters reported in
the literature. It was notable that the dibromosulfone 5b, which was obtained as a threo / erythro isomer mixture,
gave exclusively on dehydrobromination the unsaturated sulfone 2b, the configuration of which was confirmed
by reduction with zinc dust in acetic acid to the sulfone 1b. We have previously observed a similar reaction for
the dibromosulfone 5a [2].
421

TABLE 3. IR Spectra of the Compounds Synthesized*
Com-
pound
Characteristic frequencies, ν, cm-1
1b
2b
509 s, 687 m, 744 s, 760 s, 798 m, 972 s, 1115 s, 1138 s, 1277 vs, 1451 m, 1624 m,
2928 w, 3028 w, 3048 m
513 s, 528 s, 586 m, 694 s, 748 m, 760 s, 972 s, 1138 vs, 1308 vs, 1442 m, 1485 m,
1605 m, 2928 w, 3008 w, 3024 w
3b
4b
509 s, 702 s, 779 s, 964 s, 1130 vs, 1292 s, 1319 s, 1628 m, 2924 w, 3009 w, 3048 m
459 m, 509 s, 698 s, 775 m, 914 s, 1119 vs, 1269 s, 1304 vs, 1323 s, 1454 m, 2928 w,
2978 w
treo-5b
6a
436 m, 513 m, 702 s, 833 s, 952 s, 953 m, 1119 s, 1300 vs, 1312 s, 1454 m, 1493 m,
2928 m, 2978 w
529 s, 700 s, 770 m, 1140 vs (SO2, νs), 1231 m, 1262 s, 1306 s (SO2, νas), 1339 s,
2253 w (CN), 2967 m, 3029 m
6b
6c
706 m, 789 m, 1120 s (SO2, νs), 1146 m, 1236 m, 1310 s (SO2, νas), 1434 m,
1728 vs (C=O), 1747 s (C=O), 2960 w, 3012 w
702 m, 1124 s, 1155 s (SO2, νs), 1248 s, 1309 s (SO2, νas), 1330 s, 1368 w,
1712 vs (C=O), 1734 m (C=O), 3002 w
6d
7
455 m, 706 m, 889 w, 1124 s, 1157 w, 1250 s, 1310 m, 1331 w, 1717 vs, 1738 m,
2955 w, 3002 w
490 m, 540 m, 695 m, 702 m, 772 m, 1142 s, 1262 m, 1323 m, 1343 vs, 1458 w,
1501 w, 2260 vw, 2955 m, 2978 s, 3017 m
9a
478 m, 494 m, 837 m, 1103 m, 1138 s, 1211 m, 1308 m, 1325 vs, 1555 m, 1593 w,
1632 w, 2234 m, 2930 w, 2951 m, 2994 w, 3021 w
9b
11
482 m, 513 m, 536 m, 702 m, 737 m, 795 s, 972 s, 1142 vs, 1149 s, 1315 vs, 1427 m,
1446 m, 1566 m, 1585 w, 2233 m, 2935 w, 3020 w
475 m, 521 m, 706 m, 787 m, 957 m, 1046 m, 1103 s, 1146 s, 1308 vs, 1416 m, 1447 m,
1559 w, 2924 w, 2955 m, 3025 w
12
498 m, 583 m, 753 m, 768 m, 961 m, 1103 m, 1119 m, 1154 s, 1219 m, 1285 s, 1304 vs,
1451 m, 1678 s
_______
* Ten strongest and characteristic absorption bands are quoted
The CH-acids enolates were generated using NaH in THF at 20-45ºC under a dry argon atmosphere. The
broadest range of CH-acids was used in the condensation reactions with bromomethyl vinyl sulfone 1a
(dimethylmalonate, malononitrile, methyl and ethyl acetoacetate). The remaining mono- and dibromosulfones
were only studied using the malononitrile enolate.
Independently of the nature of the CH-acids the single reaction product of the reaction of the sulfone 1a
was the corresponding heterocyclization product 6a-d*2 in every case.
1
The differences in the H-4 and 2H-5 signals in the H NMR spectra of compounds 6a-d (Table 4)
deserve attention. Whereas in the case of the heterocycle 6a the expected ABX type multiplet is observed, for
compounds 6c,d a degenerate ABX multiplet is seen (approximating to the AA’X type, virtual spin-spin
couplings are given in Table 4, see [8, 9]) and this is due to the closeness of the chemical shifts of the H-5
protons and the high geminal spin spin coupling constant. The exchange of CDCl3 solvent to C6D6 causes a
1
change in the signal chemical shifts in the H NMR spectrum of compound 6d but the form of the discussed
multiplet remains as earlier: a doublet at 3.13 (J = 8.0 Hz) and triplet at 4.57 ppm (J = 7.3 Hz). The
corresponding signal for compound 6b has an intermediate form: in the X part it appears as a triplet (virtual
spin-spin coupling given in Table 4) and in the AB part it is more complex than a doublet, being a multiplet with
one of the H-2 proton signals superimposed.
_______
*2 Part of this material has been reported in [7].
422

423

424

CH2WW 1
Ph
–
Br
1a
CHWW1
–
B
SO2
A
W
Ph
–
Ph
CWW1
O
Br
W1
S
O
–
S
Br
O
O
B
6a–d
6 a W = W1 = CN; b W = W1 = CO2Me; c W = CO2Et, W1 = COMe;
d W = CO2Ме, W1 = COMe
It was notable that each of the compounds 6c and 6d is formed exclusively as one of two possible
diastereomers, in fact with a cis orientation of the phenyl and ester groups. The configuration of the
diastereomers was established on the basis of a comparison of the chemical shifts of the methoxycarbonyl
protons in the 1H NMR spectra of compounds 6b and 6d. The singlet signals of the two non-equivalent CO2Me
groups in heterocycle 6b were markedly removed one from the other and the signal corresponding to the group
shielded by the phenyl substituent (3.42 ppm) was virtually coincident with the chemical shift of the
methoxycarbonyl proton signal (3.46 ppm) in heterocycle 6d.
We explain the formation of compounds 6a-d in terms of initial Michael addition to give carbanion A
with transfer of a proton to form the more stable carbanion B (see [5]). The latter can take part in a
1,5-cyclization to form the tetrahydrothiophene S,S-dioxide. The strict stereoslectivity of the reacrions chemistry
involving the acetoacetate deserves discussion. Although the van der Waal radius of the CO2Me group (1.62 Å
[10]) somewhat exceeds that of the COMe group (1.56 Å), in the transition state (in which the carbon atom
bonded to this substituent carries a marked negative charge) the effective steric volume of the indicated groups
can be significantly different. In fact, because the acetyl group is a considerably more powerful π-acceptor than
the carbalkoxy group it delocalizes the electron density better and this leads to an inhibition of its rotation
around the C–C bond and hence simultaneously to an increase in the effective steric bulk when compared with a
similar but more mobile carbalkoxy group. Hence the latter in fact proves to be in a cis position to the phenyl
substituent in the transition state and in the reaction product.
Condensation of dibromide 2a with sodium malononitrile gave the corresponding heterocyclic
monobromide 7. The 13C NMR spectrum of bromide 7 (Table 4) is in the expected agreement with that of the
1
analogous 6a. Comparison of the H NMR spectra of compound 7 and 6a shows a strong difference in the
chemical shifts of the H-4 proton and a virtually identical position for the H-5 proton signals. Hence we can
conclude that the bromide 7 has a trans configuration with the known shielding effect of a phenyl ring and
deshielding effect of a bromine atom on oppositely placed vicinal protons.
Formation of heterocycle 7 can be rationalized by a scheme analogous to formation of compounds 6, in
fact a 1,5-cyclization of carbanion B'. Hence the presence of the vinyl bromine atom in compound 2a does not
change the direction of its reaction when compared with the sulfone 1a. For carbanion B' another type of
reaction could a priori be possible, i.e. a 1,3-cyclization, the result of which would be the formation of the
cyclopropane 8a. However, this is not realized, evidently because the 1,5-cyclization route proves to be more
favored.
425

Br
Ph
Ph
CN
CN
Ph
CN
CN
X
O
O
CN
S
–
Br
X = Br
S
S
CN
X
O
O
O
O
B'
8 a X = Br, b X = H
8a,b
7
For the methyl α-bromovinyl sulfone 2b unable to take part in a 1,5-cyclization, the main Michael
induced addition reaction route for sodium malononitrile might prove to be a 1,3-cyclization leading to the
cyclopropane 8b. However only the ethylidenemalononitrile derivative 9b is in fact formed.
Treatment of the β-bromovinyl sulfones 3a and 3b with sodium malononitrile gives exclusively the
ethylidenemalononitrile derivatives 9a and 9b respectively.
Ph
H
CH(CN)2
HBr
–
3a,b
–
Br
CH(CN)2
XCH2SO2
–
A''
Ph
Br
H
XCH2SO2
Ph
XCH2SO2
H
–
C(CN)2
10a,b
B''
CH2(CN)2
–
HBr
2b
Ph
Ph
a X = Br, b X = H
CN
XCH2SO2
XCH2SO2
CH(CN)2
C
CN
9a,b
Formation of these compounds from sulfones 3a,b might be explained as a Michael addition induced
1,2-dihydrobromination involving carbanions A" and B". However a more likely alternative route would be
initial dehydrobromination of bromides 3a,b to the ethynyl sulfones 10a,b, subsequent Michael addition of the
malononitrile, and prototropic isomerization of the adduct C. An experimental conversion of the specifically
synthesized ethynyl sulfone 10b to compound 9b under similar conditions served to support this hypothesis.
Finally, formation of the ethylidenemalononitrile 9b from the α-bromovinyl sulfone 2b can occur only via an
initial dehydrobromination with the intermediate formation of the same ethynyl sulfone 10b. The fact that both
the 1-bromovinyl sulfone 2b and the 2-bromovinyl sulfone 3b are liable to dehydrobromination to form the
same ethynyl sulfone 10b, active in a nucleophilic addition reaction, was identified by treating them with
stronger basic nucleophiles than sodium malononitrile, in fact sodium methylate in methanol and water–alcohol
alkali. The dimethyl ketal 11 was obtained in the first case and the ketone 12 in the second.
OMe
O
MeSO2
MeONa
KOH
H2O
MeSO2
2b, 3b
Ph
Ph
MeOH, ∆
MeO
12
11
426

EXPERIMENTAL
1
Elemental analysis was carried out on an HP-185B CHN analyzer. H and 13C NMR spectra were
1
obtained on a Bruker AC-300 spectrometer (300 and 75 MHz) using CDCl3 and the chemical shifts in the H
NMR spectra were measured relative to the residual solvent signal at 7.26 ppm or for compound 6a relative to
the residual DMSO-d6 signal at 2.50 ppm as the internal standards. IR spectra were taken on an Infralum FT-02
Fourier spectrometer for KBr tablets. Mass spectra were recorded on an MX 1321 instrument (70 eV electron
ionization energy) for compound 7 and the remainder on an Agilent 6890N chromatograph with mass selective
detector (equipped with a 30 m Agilent 19091S-433 HP-5MS capillary column of internal diameter 0.25 mm,
5% phenylmethylsiloxane, temperature program to 325ºC, and helium gas carrier (1 ml/min)).
TLC was carried out on Silufol UV-254 plates in the system hexane - diethyl ether (1:1) and revealed
using iodine vapor or UV light. A DRT-400 mercury lamp was used for the photochemical reactions.
Photochemical Reaction of Styrene with Methanesulfobromide. Freshly distilled styrene (1.9 g,
18 mmol) and MeSO2Br [11], (2.86 g, 18 mmol) in anhydrous CH2Cl2 (15 ml) were placed in a quartz test tube.
The reaction mixture was irradiated with UV light for 10 h at 20ºC. Solvent was removed in vacuo and the solid
compound was purified by crystallization to give the sulfone 4b (2.6 g).
Dehydrobromination Reaction of Compound 4b. A solution of Na2CO3 (9.1 g, 86 mmol) in water
(50 ml) was added to a solution of compound 4b (17.1 g, 65 mmol) in dioxane (50 ml), stirred for 20 h at 20ºC,
and then diluted with water (150 ml). The finely crystalline solid was filtered off, washed with water (100 ml),
and dried in air to give compound 1b (10.2 g). Its 1H and 13C NMR spectra were identical to those given in [2].
Bromination of Compound 1b. A solution of bromine (3.52 g, 22 mmol) in anhydrous CH2Cl2 (4 ml)
was added with stirring to a solution of compound 1b (4.0 g, 22 mmol) in CH2Cl2 (30 ml). Stirring was
continued for 30 h at 20ºC. Removal of solvent in vacuo gave the semicrystalline material 5b (4.14 g) as a 2.4:1
1
mixture of the erythro and threo diastereomers (from their H NMR spectra) with an admixture of the starting
sulfone 1b. The minor (threo isomer) component was separated by crystallization. The main (erythro isomer)
was separated as an oil with a stereochemical purity of 85%.
Dehydrobromination of the Dibromosulfone 5b. A solution of Na2CO3 (1.27 g, 12 mmol) in water
(15 ml) was added to a solution of the mixture of compound 5b diastereomers (3.42 g, 10 mmol) in dioxane
(15 ml), stirred for 20 h at 20ºC, and then diluted with water (100 ml). The finely crystalline precipitate was
filtered off, washed with water (50 ml), and dried in air to give the sulfone 2b (2.1 g).
Hydrodebromination of Compound 2b. Zinc dust (0.15 g, 2.3 mmol) was added to a solution of
compound 2b (1.15 g, 4.4 mmol) in 1:1 aqueous acetic acid (2 ml). The reaction mixture was refluxed with
stirring for 50 min, zinc dust was again added (0.16 g, 2.5 mmol), and stirring was continued under the same
conditions for a further 1 h. The cooled reaction mixture was diluted with water (80 ml) and extracted with
CHCl3 (3×20 ml). The extract was dried over MgSO4 and the solvent was removed in vacuo. Crystallization
gave the sulfone 1b (0.36 g, 45%).
Photochemical Reaction of Phenylacetylene with Methanesulfobromide. Freshly distilled
phenylacetylene (2.0 g, 20 mmol) and MeSO2Br (3.2 g, 20 mmol) were dissolved in anhydrous CH2Cl2 (10 ml)
in a quartz test tube. The tube was tightly covered and irradiated with UV light for 26 h at 20ºC. After
distillation of solvent the semicrystalline residue was washed with ether (10 ml) to give the bromosulfone 3b
(1.83 g) with mp 66-67ºC (from a mixture of chloroform and CCl4). Mp reported in [6] was 60-61ºC (ethanol).
Reaction of Compound 1a with CH-Acids (General Method). A suspension of NaH (60%, 0.17 g,
4.2 mmol) in mineral oil was washed with dry hexane. Solvent was removed by decantation and the remainder
in vacuo. The vacuum was purged by the introduction of argon and was added of dry THF (5 ml). A solution of
the CH- acid (3.8 mmol) in THF (10 ml) was added dropwise with stirring and cooling to 5ºC. The reaction
mixture was stirred in the case of the malonic acid derivatives for 1 h at 20ºC and for the acetoacetic
427

derivatives for 3 h at 45ºC. A solution of the sulfone 1a (3.8 mmol) in THF (10 ml) was added dropwise and the
product was stirred for 20 h at 20ºC, diluted with water (250 ml), and neutralized with dilute (1:1) HCl. The
precipitate was filtered off, washed with water, dried in air, and purified by crystallization.
Reaction of Compound 2a with Malononitrile. A solution of sodium malononitrile in THF (10 ml)
was prepared from a 60% suspension of sodium hydride (0.23 g, 5.8 mmol) in mineral oil and malononitrile
(0.18 g, 2.8 mmol). A solution of compound 2a (0.84 g, 2.5 mmol) in THF (10 ml) was added and the mixture
was stirred for 20 h at 20ºC after which it was diluted with water (250 ml), and neutralized with dilute (1:1) HCl.
The precipitate was filtered off, washed with water, dried in air, and crystallized to give compound 7 (0.41 g).
Reaction of Acetylene 10b with Malononitrile. A solution of sodium malononitrile in THF (10 ml)
was prepared from a 60% suspension of sodium hydride (0.15 g, 3.8 mmol) in mineral oil and malononitrile
(0.22 g, 3.4 mmol). A solution of acetylene 10b [6] (0.56 g, 3.1 mmol) in THF (10 ml) was added and the
mixture was stirred for 18 h at 20ºC after which it was diluted with water (180 ml), neutralized with dilute (1:1)
HCl and extracted with CHCl3 (3×15 ml). The extracts were washed with water and dried over MgSO4.
Removal of solvent and crystallization gave compound 9b (0.21 g, 28%).
Reaction of Compound 2b with Malononitrile. A solution of sodium malononitrile in THF (10 ml)
was prepared from a 60% suspension of sodium hydride (0.25 g, 6.2 mmol) in mineral oil and malononitrile
(0.22 g, 3.4 mmol). A solution of compound 2b (0.8 g, 3.1 mmol) in THF (10 ml) was added and the mixture
was stirred for 2.5 h after which it was diluted with water (200 ml), neutralized with dilute (1:1) HCl, extracted
with CHCl3, washed with water, and dried over MgSO4. Evaporation of solvent in vacuo gave 0.45 g of a
viscous oil which was recrystallized to give compound 9b (0.27 g, 36%).
Reaction of Compounds 3a and 3b with Malononitrile (General Method). A solution of
malononitrile (0.2 g, 3.0 mmol) in THF (10 ml) was added dropwise with stirring and cooling to 5ºC over
10 min under a dry argon atmosphere to a 60% suspension of NaH (0.25 g, 6.2 mmol) in mineral oil which had
been washed and dried as reported above. Stirring was continued for 1 h at 20ºC. A solution of compound 3a or
3b (2.7 mmol) in THF (10 ml) was added and stirred at 20ºC for a further 20 h, diluted with water (200 ml), and
neutralized using dilute (1:1) HCl. The precipitated ethylidene compound 9a or 9b was filtered off, washed with
water, dried in air, and purified by crystallization.
Reaction of Compounds 2b and 3b with Sodium Methylate (General Method). Either compound 2b
or 3b (0.31 g, 1.2 mmol) was added to a solution of sodium methylate prepared from metallic sodium (0.11 g,
4.8 mmol) and anhydrous methanol (5 ml). The mixture was refluxed for 30 min, neutralized using 1:1 HCl
solution with thymol blue, diluted with water (30 ml), and extracted with CH2Cl2 (3×10 ml). The extract was
washed with water and dried over MgSO4. Solvent was removed in vacuo. Crystallization of the solid residue
gave about 0.23 g of compound 11.
Reaction of sulfone 2b with KOH. The sulfone 2b (1.15 g, 4.4 mmol) was added to a solution of KOH
(0.24 g, 4.4 mmol) in a mixture of methanol (15 ml) and water (5 ml). The product was stirred for 5 h at 20ºC,
diluted with water (20 ml), and extracted with CHCl3 (3×10 ml). The extracts were washed with water and dried
over MgSO4 to give the ketone 12 (0.61 g) with mp 105-106ºC (a mixture of chloroform and CCl4). The melting
point is given as 106-107ºC in [12].
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