Novel synthesis of pinacols and sulfones promoted by Smi￡ NiCl2 bimetallic system

Article abstract of DOI:10.1002/aoc.1763

Smi￡NiCl₂ as a reductive system promoted reductive coupling of aryl adehydes and aryl ketone into pinacols in good yields and also promoted coupling reaction of aryl sulfonyl chlorides and active halides into sulfones in good yields.

Full text of DOI:10.1002/aoc.1763

Full Paper
Received: 19 September 2010
Revised: 9 November 2010
Accepted: 14 November 2010
Published online in Wiley Online Library: 17 February 2011
(wileyonlinelibrary.com) DOI 10.1002/aoc.1763
Novel synthesis of pinacols and sulfones
promoted by Sm–NiCl2 bimetallic system
Yuyuan Ye, Qizhong Zhou∗, Renhua Zheng, Huajiang Jiang, Rener Chen∗
and Yongmin Zhang
Sm–NiCl2 as a reductive system promoted reductive coupling of aryl adehydes and aryl ketone into pinacols in good yields and
c
also promoted coupling reaction of aryl sulfonyl chlorides and active halides into sulfones in good yields. Copyright ꢀ 2011
John Wiley & Sons, Ltd.
Keywords: Sm-NiCl2; reductive coupling; pinacols; sulfones; bimetallic system
Introduction
tellurium anion promoted coupling reaction of arylsulfonyl chlo-
ride and haloalkane. Fry reported synthesis of sulfones with
alkylmagnesium and alkylcopper reagents.[41] Recently, Huang
reported solid-phase synthesis of β-keto sulfones.[42]
Pinacols are useful synthons in organic synthesis. Recently,
novel calixarene hemisphere were synthesized via pinacol rear-
rangement of [2.1.2.1]metacyclophane.[1] Pinacol rearrangement
generated the pinacolone products.[2] Pinacol–pinacolone rear-
rangement of various pinacols was efficiently performed using
ZnCl2 supported on silica.[3] (+)-Austrodoral and (+)-austrodoric
acidweresynthesizedviadiastereoselectiveroutestowardtheaus-
trodorane skeleton based on pinacol rearrangement.[4] Isoxazole-
directed pinacol rearrangement was a stereocontrolled approach
to angular stereogenic centers.[5] Asymmetric addition of cy-
cloalkenyl boronic pinacol esters to aldehyde with ortho-cycloalkyl
substituted diol as a chiral ligand fabricated chiral alcohol.[6] The
(R,R)-diol diphosphane worked more efficiently in the rhodium-
catalyzed asymmetric hydrogenation of α-acetamidocinnamic
acid.[7] SmI2-mediated pinacol macrocyclization was the key step
for the synthesis of the polyfused medium-sized CDE ring system
of lancifodilactone G.[8] The prins–pinacol annulation method was
applied in the synthesis of oxaspirobicycles which exist in many
natural products.[9] Pinacol coupling, which was described in 1859,
isstillaversatilemethodtoconstructcarbon–carbonbonds.[10–25]
Sulfones are also useful synthons in organic synthesis.[26] Vinyl
sulfone-modified pyranoses and furanoses were unlimited and
versatile source of chiral building blocks.[27] Both allylic sulfones
and the disulfone intermediates were the key synthons for
carotenoid synthesis.[28,29] C15–C25 fragment of sulfone was the
key synthon for total synthesis of (+)-lasonolide.[30] Asymmetric
Aza–Michael addition of chiral hydrazines to alkenyl sulfones
followed by N–N bond cleavage and N protection and then
α-alkylation generated α-alkylated β-amino sulfones.[31] Solid-
phasesupportedsulfonesastracelesslinkerswereefficienttoolsto
synthesizetargetmoleculesornaturalproducts.[32] Yaodeveloped
a novel strategy for solid-phase synthesis of a small-molecule
library based on the vinyl sulfone scaffolds.[33]
Samarium metal is very active in organic synthesis. Re-
cently Zhang reported many organic reactions promoted by
samarium.[43–49] Banik reported that Samarium induced reduc-
tive dimerization of methyl cinnamate to synthesize 2,8-diamino
chrysene[50] and that samarium–NBS induced reductive dimer-
ization of carbonyl compounds to fabricate pinacols.[51,52] Jia
reportedthatsamariumpromotedacylationofprimary,secondary,
allyl and benzyl alcohols with acid chlorides to give esters,[53]
that samarium promoted C-acetylation of Baylis–Hillman adducts
in the presence of FeCl3 and iodine[54] and that samarium-
promotedreductionofnitroareneswitharylaldehydesformedC,N-
diarylnitrones.[55] Zhang reported samarium-promoted coupling-
cyclization of chalcones.[56] In this work, we developed a novel
Sm–NiCl2 bimetallic system to promote reductive coupling of
aryl aldehydes/aryl ketone into pinacols and to promote coupling
reaction of aryl sulfonyl chlorides and active halides into sulfones.
Experimental
General Procedure for the Synthesis of Pinacols
Arylaldehydesorarylketone(1 mmol)wereaddedtoasuspension
of Sm powder (0.15 g, 1 mmol) and NiCl2 powder (0.13 g, 1 mmol)
inanhydrousTHFwasdistilledfromsodium(10 ml)undernitrogen
atmosphere. Themixturewasstirredatroomtemperaturefor10 h.
Then water (10 ml) was added. The mixture was extracted with
ether (20 ml × 3). The organic phase was washed with brine and
dried over anhydrous Na2SO4. After distillation of the solvent, the
mixture was subjected to preparative TLC. The known compounds
(2a–2g) were similarly characterized by comparing their NMR and
IR spectra with those found in the literature.
The classic method to synthesis of sulfone is oxidation of
thioether or sulfoxide.[34] Other main methods include nucle-
ophilic substitution of sulfinate with haloalkane,[35] Friedel–Crafts
reaction of sulfonyl chloride with benzene,[36] rearrangement of
sulfinate[37] andradicaladditionofsulfonylchloridetounsaturated
hydrocarbon compounds.[38] Suzuki[39] and Huang[40] reported
∗
Correspondence to: Qizhong Zhou and Rener Chen, Department of Chemistry,
Taizhou University, Taizhou 317000, China. E-mail: qizhongchou@yahoo.com;
cre@tzc.edu.cn
Department of Chemistry, Taizhou University, Taizhou 317000, China
c
Appl. Organometal. Chem. 2011, 25, 331–334
Copyright ꢀ 2011 John Wiley & Sons, Ltd.

Y. Ye et al.
OHOH
OHH
OHOH
OHR
O
O
Sm/NiCl2
Sm/NiCl2
Ph
Ph
Ph
Ph
Ar
Ar
Ar
Ar
+
+
Ph
H
Ar
R
THF
r.t.
THF
r.t.
H H
43%
meso
H OH
R
R
R
OH
dl
1
meso
57%
dl
2a-2h
Scheme 1. Reductive coupling of benzyl aldehyde.
Scheme 2. Synthesis of various kinds of pinacols from arylketones using
Sm/NiCl2.
Table 1. Reductive coupling of aromatic aldehydes and ketone with
Sm–NiCl2 bimetallic system
O
S
O
Sm/NiCl2
Ar
Cl
Ar S R
+
Entry
Ar
R
Product
Yield (%)a
DL:mesob
RX
4
THF
50-60 °C
O
3
O
5a-5g
1
2
3
4
5
6
7
C6H5
H
2a
2b
2c
2d
2e
2f
71
78
73
77
67
75
70
57 : 43
55 : 45
54 : 46
52 : 48
50 : 50
53 : 47
55 : 45
p-ClC6H4
m-ClC6H4
p-BrC6H4
p-CH3C6H4
o-BrC6H4
C6H5
H
Scheme 3. Synthesis of various kinds of sulfones from aryl sulfonyl
chlorides and active halides using Sm/NiCl2.
H
H
H
143–145 ◦◦C); 5f, m.p. 50–51 ◦C (lit.,[67] 50–52 ◦C); 5g, m.p.
H
109–110 C (lit.,[67] 108–109.5 ◦C).
CH3
2g
a Isolated yield. b Ratios determined from the intensities of benzylic
protons in 1H NMR spectra (entries 1–6), in which the protons of DL
isomer appeared at a higher magnetic field compared with that of
meso isomer, and from the intensities of methyl protons in 1H NMR
spectra (entry 7), in which the methyl protons of DL isomer appeared
at higher magnetic field, compared with that of meso isomer.
Results and Discussion
We reported the reductive cleavage of S–S bond promoted by
the Sm–NiCl2 system.[68] Can this system be used in the reductive
coupling of aryl aldehydes or ketone? Benzyl aldehyde was added
into a suspension of Sm powder and NiCl2 powder in anhydrous
THF under nitrogen atmosphere. After the mixture was stirred at
room temperature for 10 h, Sm powder disappeared. Then water
was added. We found that a new spot appeared on TLC. We were
pleased to obtain the new product in 71% yield with preparative
TLC. According to 1H NMR, the DL:meso ratio of the pinacols is
57 : 43 (see Scheme 1). With the above method, we synthesized
several kinds of pinacols (see Scheme 2 and Table 1).
Aryl aldehydes or aryl ketone afforded pinacols in good yields.
Can this system be used in the coupling of aryl sulfonyl chlorides
with active halides? Fortunately, we synthesized several kinds of
sulfones from aryl sulfonyl chlorides with active halides promoted
by Sm–NiCl2 with the above-mentioned method (see Scheme 3
and Table 2).
2a, lit.[57]; 2b, lit.[58]; 2c, lit.[59]; 2d, lit.[60]; 2e, lit.[58]; 2f, lit.[61]; 2g,
lit.[57]
General Procedure for the Synthesis of Sulfones
Active halides (1.2 mmol) were added into a suspension of Sm
powder (0.17 g, 1.1 mmol), NiCl2 powder (0.143 g, 1.1 mmol) and
aryl sulfonyl chloride (1.0 mmol) in anhydrous THF (10 ml) under
nitrogen atmosphere. The mixture was stirred at 50–60 ◦C for
2–3 h. Then water (10 ml) was added. The mixture was extracted
with ether (20 ml × 3). The organic phase was washed with
brine and dried over anhydrous Na2SO4. After distillation of
the solvent, the mixture was subjected to preparative TLC.
The known compounds (5a–5g) were similarly characterized by
comparing their NMR and IR spectra with those found in the
literature
All active halides (entries 1–7) reacted with aryl sulfonyl halides
afforded sulfones in good yields except butylbromide (entry 8)
in 0 yield, although Zhang reported synthesis of sulfones with
Sm–HgCl2 bimetallic system from arylsulfonyl chlorides and alkyl
halides.[69] Hg and HgCl2 are prohibited in industry as they are
very poisonous and cause severe environmental pollution. NiCl2
5a, m.p. 145–146 ◦C (lit.,[62] 146◦–146.5 ◦C); 5b, m.p. 41–42 ◦C
(lit.,[63] 42–43 ◦C); 5c, m.p. 93◦–94 C (lit.,[64] 93–95 ◦C); 5d, m.p.
208–210 ◦C (lit.,[65] 209–211 C); 5e, m.p. 143–144 ◦C (lit.,[66]
Table 2. Coupling of aryl sulfonyl chlorides and active halides with Sm–NiCl2 system
Entry
Ar
C6H5
RX
Time (h)
Temperature (◦C)
Product
Yield (%)a
1
2
3
4
5
6
7
8
C6H5CH2Br
2
2
2
3
2
2
3
5
50
50
50
60
60
50
50
60
5a
5b
5c
5d
5e
5f
74
71
75
67
71
68
73
0
C6H5
BrCH2COOC2H5
C6H5COCH2Br
p-NO2C6H5CH2Br
C6H5CH2Br
C6H5
C6H5
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
CH2 CHCH2Br
C6H5COCH2Br
CH3(CH2)2CH2Br
5g
a Isolated yield.
c
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Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 331–334

Novel synthesis of pinacols and sulfones
Sm2+
Sm
+ NiCl2
O
O
Sm2+
Ar C R +
Sm3+
O R
+
Ar
R
1
a
O
O O
OHOH
OHR
H+
Ar C R
Ar
Ar
Ar
Ar
+
Ar
Ar
Ar
Ar
+
R
meso
R
R
O
R
meso
R
R
OH
dl
dl
b
2
Scheme 4. Possible reaction mechanism of reductive coupling of aryl aldehydes and aryl ketone promoted by Sm–NiCl2 bimetallic system.
[4] E. Alvarez-Manzaneda, R. Chahboun, I. Barranco, E. Cabrera,
E. Alvarez, A. Lara, R. Alvarez-Manzaneda, M. Hmamouchic, H. Es-
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Sm
+ NiCl2
Ni*
Ni*
[ArSO2 ]2Ni2+
RX
-
ArSO2R
ArSO2Cl +
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5
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Scheme 5. Possible reaction mechanism of coupling of aryl sulfonyl
chlorides and active halides promoted by Sm–NiCl2 bimetallic system.
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and Ni are widely used in industry and are less poisonous. The
use of Sm–NiCl2 offers advantages over the Sm–HgCl2 previously
reported.
The possible reaction mechanism of reductive coupling of aryl
aldehydes and aryl ketone mediated by Sm–NiCl2 are given in
Scheme 4. NiCl2 oxidized Sm to Sm2+. In situ-generated Sm2+
reacted with aryl aldehydes or aryl ketone to form radical carbon
anion a and Sm3+. Then radical carbon anion a dimerized into b
followed by protonation to form pinacol 2 in meso and DL form
(see Scheme 4).
The possible reaction mechanism of coupling of aryl sulfonyl
chlorides and active halides mediated by Sm–NiCl2 is explained in
Scheme 5. Sm reduced NiCl2 to active Ni∗. In situ-generated active
Ni∗ reacted with aryl sulfonyl chlorides to form aryl sulfonyl anion.
Then aryl sulfonyl anion attacked active halides to form sulfones 5
(see Scheme 5).
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In summary, we developed novel methods to synthesize pinacols
from aryl aldehydes and aryl ketone in good yields and synthesize
sulfones from aryl sulfonyl chlorides and active halides in good
yields with an Sm–NiCl2 bimetallic system. The main advantages
of the present procedure are the milder reaction conditions and
simple operation. The further utility of the Sm–NiCl2 bimetallic
system in organic synthesis was under study.
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We are grateful to the Natural Science Foundation of Zhejiang
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