The catalyzed desulfinylative allylation of carbonyl compounds with alk-2-enesulfonyl chlorides and silyl alk-2-enesulfinates

Article abstract of DOI:10.1002/chem.201000705

Coupling up with sulfonyl chlorides: An ene reaction of alkenes with SO₂·BCl₃ permits the one-pot conversion of simple alkenes into b,g-unsaturated sulfonyl chlorides or sulfinic silyl esters. These compounds can then be used as nucleophilic allylating agents with aldehydes and ketones to generate the corresponding homoallylic alcohols (see scheme) with good chemo-and diastereoselectivity in the presence of a suitable catalyst and reducing agent.

Full text of DOI:10.1002/chem.201000705

DOI: 10.1002/chem.201000705
The Catalyzed Desulfinylative Allylation of Carbonyl Compounds with Alk-
2-enesulfonyl Chlorides and Silyl Alk-2-enesulfinates
Chandra M. R. Volla, Dean Markovic´, Sylvain Laclef, and Pierre Vogel*[a]
Carbon–carbon cross-coupling reactions are very impor-
tant in the areas of material science and medicinal chemis-
try.[1] Transition-metal-catalyzed cross-coupling of organo-
metallic reagents (nucleophiles) with halides or triflates
monoalkenes with sulfur dioxide,[10] substrates 1–4 have
become powerful electrophilic allylating agents (without
BCl3, the ene reaction of simple monoalkenes with SO2 is
endergonic above À1008C).[11] We have recently reported
À
(electrophiles) constitutes one of the most powerful meth-
that iron catalysts can be used in the desulfinylative C C
[2]
À
ods for constructing C C bonds. Arene- and alkanesulfon-
cross-coupling reaction of Grignard reagents with alkane-,
alkene-, and arenesulfonyl chlorides[12] and with alk-3-ene-
sulfonyl chlorides.[13]
yl chlorides are inexpensive and readily available com-
pounds. We have shown that Stille, carbonylative Stille,[3]
Suzuki–Miyaura,[4]
Sonogashira–Hagihara,[5]
Mizoroki–
In 1977, Nozaki and co-workers[14] reported the chemose-
lective allylation of aldehydes with allyl halides mediated by
CrCl2. The reaction was then extended to the alkenylation[15]
and alkynylation[16] of carbonyl compounds. Alkenyl triflates
can also be used in this type of reaction under nickel cataly-
sis.[17] The reaction requires two equivalents of CrCl2 to
reduce the allyl halides into allylchromium complexes[18]
that then add to the carbonyl compounds, like other allyl–
metal species, through a Zimmermann–Traxler-like transi-
tion state.[19] Alternative mechanisms implying radical inter-
mediates[20] and oxidation/reduction equilibria (Oppenauer–
Meerwein–Ponndorf–Verley-type mechanism) have been
proposed.[21] These alternative mechanisms suggested to us
that CrCl2 might induce desulfinylation of alk-2-enesulfonyl
Heck,[6] and Negishi[7]-type cross-couplings can all be carried
out by using sulfonyl chlorides as the electrophilic partners
under desulfinylative conditions.[8] We have also shown that
2-methylprop-2-ene- (1), prop-2-ene- (3), and (E)-but-2-ene-
sulfonyl chlorides (4) are useful electrophilic partners in de-
À
sulfinylative palladium-catalyzed C C coupling reactions
with inexpensive Grignard reagents and sodium salts of ma-
lonic esters and methyl acetoacetate.[9] As these sulfonyl
chlorides can be prepared in one-pot operations (Scheme 1)
through a BCl3-promoted ene reaction of the corresponding
chlorides generating allylchromiumACTHNUTRGNEUNG(III) intermediates that
could be used as nucleophilic partners in carbonyl-com-
pound allylation, thus creating umpolung[22] reactivity by
converting allyl–SO2Cl compounds (C-electrophile) into
allyl–metal compounds (C-nucleophile; Scheme 2).
When we reacted 2-methylprop-2-enesulfonyl chloride (1)
in THF at room temperature with a) benzaldehyde, b) para-
Scheme 1. The one-pot synthesis of alk-2-enesulfonyl chlorides.[10]
´
[a] Dr. C. M. R. Volla, Dr. D. Markovic, S. Laclef, Prof. P. Vogel
Laboratoire de glycochimie et de synthꢀse asymꢁtrique (LGSA)
Ecole Polytechnique Fꢁdꢁrale de Lausanne (EPFL)
Batochime, CH 1015 Lausanne (Switzerland)
Fax : (+41)21-693-93-75
E-mail: pierre.vogel@epfl.ch
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000705.
Scheme 2. The CrCl2-mediated conversion of electrophilic sulfonyl chlor-
ides into nucleophilic allylating agents.
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Chem. Eur. J. 2010, 16, 8984 – 8988

COMMUNICATION
chlorobenzaldehyde, and c) phenylacetaldehyde in the pres-
ence of two equivalents of CrCl2, the corresponding homoal-
lylic alcohols 7a–c were formed as the sole products of the
reaction and isolated in 70, 63, and 55% yields, respectively
(Scheme 3). As with other Nozaki–Hiyama-type reactions,
the stoichiometric CrCl2 can be replaced by Mn (metal) and
Me3SiCl, allowing the use of CrCl2 as a catalyst.[23] Indeed
we found that 1 reacted with benzaldehyde in the presence
of Mn (3 equiv) and Me3SiCl (2 equiv) in THF at room tem-
perature to afford 7a in 62% yield.
We then applied the conditions with the best yield for the
reaction (Table 1, entry 4) to various carbonyl compounds
using both 2-methylprop-2-enesulfonyl chloride (1) and
prop-2-enesulfonyl chloride (2). Our results are summarized
in Table 2 and show the versatility of the method as a wide
range of aliphatic and aromatic aldehydes and ketones can
be allylated in good yields.
By using a mixture of (E)- and (Z)-but-2-enesulfonyl
chloride (3; 3:1), we studied the regio- and diastereoselectiv-
ity of the allylation of benzaldehyde (Table 3). Under our
standard conditions (Table 1, entry 4: PdACHTUNRGTNEUNG(OAc)2/nBu3P in
hexane/toluene), a 1:1:2 mixture of the three possible homo-
Table 2. Pd-catalyzed reductive and desulfinylative allylations of carbon-
yl compounds with 1 and 2.[a]
Scheme 3. CrCl2-catalyzed reductive allylation of benzaldehyde with 2-
methylprop-2-enesulfonyl chloride.
We then explored whether the toxic CrCl2 could be re-
moved completely. Since we have previously observed that
alk-2-enesulfonyl chlorides undergo fast desulfinylation in
the presence of palladium complexes,[9] generating electro-
philic allylpalladium intermediates, we searched for reducing
agents capable of converting these into C-nucleophiles (all-
RSO2Cl Carbonyl
compound
Yield Product R1
[%][b]
R2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1
1
1
1
1
1
1
1
1
2
2
2
2
2
4-ClC6H4CHO
4-EtC6H4CHO
4-MeOC6H4CHO 68
PhCH2CHO
n-C10H21CHO
c-C6H11CHO
PhCOMe
76
77
7b
7e
7d
7c
7 f
7g
7h
7i
H
H
H
H
H
H
4-ClC6H4
4-EtC6H4
4-MeOC6H4
PhCH2
n-C10H21
c-C6H11
ACHTUNGTRENNUNG
59
65
72
65
67
63
81
75
69
72
–
AHCTUNGTRENNUNG
Me Ph
Ph
as the catalyst, 7a was not found in the crude reaction mix-
PhCOPh
Ph
À
ture after 24 h at 258C.[26] In hexane/toluene (4:1) with
À
G
cyclohexanone
4-PhC6H4CHO
4-PhOC6H4CHO
PhCH2CHO
4-FC6H4COPh
PhCOOMe
7j
Et2Zn and using either [PdACHTNUGTRENN(GU Ph3P)4] or PdAHCTUNGTERN(NUNG OAc)2/nBu3P
8a
8b
8c
8d
–
4-PhC6H4
4-PhOC6H4
PhCH2
4-FC6H4
–
(Table 1, entries 2 and 4, respectively) as the catalyst system
the reaction led to the formation of homoallyl alcohol 7a in
good yields. If hexane alone was used as the solvent
(Table 1, entry 5), the reaction was slower, whilst without a
phosphane ligand in the reaction (Table 1, entries 3 and 7)
[a] Conditions: 1 (1 mmol ) and the carbonyl compound (1.2 mmol) in
hexane/toluene (4:1; 5 mL). [b] Isolated yield after flash column chroma-
tography on silica gel.
the yield dropped. Interestingly, if [PdCl2ACHTNUTRGNE(UNG PhCN)2] was used
as the catalyst, SnCl2 was a suitable reductant for this allyla-
tion by umpolung reaction (Table 1, entry 8).[27] As expect-
ed, if Et2Zn or SnCl2 were replaced by ZnCl2, no allylation
was observed (Table 1, entry 6).
Table 3. Regio- (9 vs. 10) and diastereoselectivity (syn-9 vs. anti-9) of the
reductive and desulfinylative Pd-catalyzed allylation of aldehydes with
but-2-enesulfonyl (3) and 1-methylprop-2-enesulfonyl chloride (4).
Table 1. Palladium-catalyzed reductive and desulfinylative allylation of
benzaldehyde with 2-methylprop-2-enesulfonyl chloride 1 at 258C.[a]
Catalyst (5 mol%)/ Reductant Solvent
ligand (10 mol%) (3 equiv)
t
Yield
[%][b]
AHCTUNGTRENNUNG
1
2
3
4
5
6
7
8
[Pd
[Pd
ACHTUNGTRENNUNG[Pd CHTUNGTRENNUNG
N
In
THF
24 h
–
Et2Zn
Et2Zn
Et2Zn
Et2Zn
ZnCl2
Et2Zn
SnCl2
hexane/toluene[c] 25 min 62
hexane/toluene[c] 25 min traces
hexane/toluene[c] 15 min 85
RSO2Cl Aldehyde
Solvent
Yield Product R2
[%][a] ratio[b]
Pd
Pd
Pd
N
CHTUNGTRENNUNG
1
2
3
4
5
3 or 4
3
3
3 or 4
3 or 4
PhCHO
PhCHO
PhCHO
PhCHO
hexane/toluene 75
toluene
THF
1:1:2
1:1:2
Ph
Ph
C
hexane
hexane/toluene[c] 24 h
hexane/toluene[c] 30 min 15[e]
THF 24 h 65
30 min 47
44
69
73
68
G
–
2:1:0
Ph
N
CHTUNGTRENNUNG
DME
2.5:1:0
2.3:1:0
Ph
c-C6H11
E
CHTUNGTRENNUNG
c-C6H11CHO DME
[a] Conditions: 1 (1 mmol) and PhCHO (1.2 mmol) in solvent (5 mL).
[b] Yield after purification by column chromatography on silica gel.
[c] 4:1 hexane/toluene. [d] dba=dibenzylideneacetone. [e] Yield by
1H NMR spectroscopy of the crude product.
[a] Yield of the product mixture by flash column chromatography on
silica gel. [b] The anti-9/syn-9/10 product ratio was determined by
1H NMR spectroscopy of the crude reaction mixture.
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8985

P. Vogel et al.
allylic alcohols anti-9a, syn-9a, and 10a was obtained in a
75% combined yield (Table 3, entry 1).
The same yield and product ratio were obtained if 4 was
used instead of 3, which supports the possible mechanism
shown in Scheme 4 by implying the formation of the same
ladium complex 15 and Me3SiOAc (Scheme 6). Complex 15
was then converted, at 258C, into sulfone 16. On adding a
further 0.5 equivalents of Ph3P, 15 was converted into 17
and SO2. These experiments suggested that silyl sulfinate 13
reacts with palladium, generating allylpalladium intermedi-
ates that could be used as nucleophilic allylating reagents.
Scheme 6. Known reactions of Pd
sulfinates.
ACHTUNGTRNE(NUNG OAc)2/PPh3 with b,g-unsaturated silyl
Scheme 4. A possible mechanism for the reductive (Et2Zn) and desulfiny-
lative allylation of benzaldehyde with alk-2-enesulfonyl chlorides;
DME=dimethoxyethane.
If 13 or 14 were reacted with benzaldehyde and catalytic
amounts of Pd(OAc)2/nBu3P, the corresponding homoallylic
AHCTUNGTRENNUNG
alcohols 7a (3-methyl-1-phenylbut-3-enol) and 8e (1-phenyl-
but-3-enol) were formed in low yields (<10%). This failure
suggests that a stronger Lewis acid must be added to en-
hance the electrophilicity of the aldehyde. After several un-
successful attempts, we found that the use of [PdCl2-
but-2-en-1-yl–palladium intermediate 11 starting from either
3 or 4. Transmetallation generates butenylzinc intermediate
12, which allylates the carbonyl compounds. Interestingly,
whereas the formation of homoallylic alcohol 10 competed
with the generation of products 9 in non-polar solvents
(Table 3, entries 1 and 2), product 10 was not visible if more
polar solvents such as THF (Table 3, entry 3) or DME
AHCTUNGTERGNUN(N PhCN)2] as the precatalyst (5 mol%), in the presence of
SnCl2, in THF permitted the nucleophilic allylation of
PhCHO with both sulfinates 13 and 14, giving 7a and 8e in
75 and 71% yields, respectively (Table 4, entries 1 and 2).
The reaction was extended to 4-chlorobenzaldehyde
(Table 4, entry 3) and aliphatic aldehydes such as undecanal
(Table 4, entry 4) and phenylacetaldehyde (Table 4, entry 5).
Further work will have to be carried out to find a promoter
that does not have to be used in excess, as was required
here (3 equivalents of SnCl2).
(Table 3, entries 4 and 5) were used. If [Pd
ACHTUGNTREN(UNNG Ph3P)4] was used
as the catalyst instead of Pd(OAc)2/nBu3P, the product ratio
AHCTUNGTRENNUNG
was 1:1:1 (syn-9/anti-9/10). The reaction of 1-methylprop-2-
enesulfonyl chloride 4 with benzophenone formed the corre-
sponding homoallylic alcohol 9c in 35% yield (Scheme 4).
b,g-Unsaturated silyl sulfinyl esters can be obtained readi-
[28]
ly by an ene reaction of allylsilanes with SO2 and as inter-
mediates in the cocondensation of SO2 with electron-rich
1,3-dienes and alkenes.[29,30] As these compounds can also be
obtained by the H-ene reaction of alkenes with SO2/BCl3,
followed by neutralization with NH3 and reaction with silyl
chlorides[10] (Scheme 5), we wondered whether these systems
could be employed as nucleophilic allylating agents.
A possible mechanism for the allylation of aldehydes with
silyl alk-2-enesulfinates is proposed in Scheme 7. After re-
Table 4. Pd-catalyzed desulfinylative allylation of aldehydes with trime-
thylsilyl 2-methylprop-2-enesulfinate (13) and trimethylsilyl prop-2-ene-
sulfinate (14).
Preliminary studies within our group[31] have shown that
silyl sulfinate 13 reacts with PdACHTUNTRGNEUNG(OAc)2/Ph3P to give allylpal-
Sulfinate
Aldehyde
Yield
[%][a]
Product
R2
1
2
3
4
5
13
14
13
13
14
PhCHO
PhCHO
4-ClC6H4CHO
n-C10H21CHO
PhCH2CHO
75
71
67
72
58
7a
8e
7b
7 f
8 f
Ph
Ph
4-ClC6H4
n-C10H21
PhCH2
Scheme 5. The preparation of b,g-unsaturated silyl sulfinates through an
H-ene reaction of SO2·BCl3.
[a] Yield of isolated product after flash column chromatography on silica
gel.
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Chem. Eur. J. 2010, 16, 8984 – 8988

Desulfinylative Allylation
COMMUNICATION
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À
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´
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suitable reagents for the palladium-catalyzed reductive and
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a catalyst in the presence of metallic Mn and trimethylsilyl
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Acknowledgements
We are grateful to the Swiss National Science Foundation (Grants
200020 124724 and 200021 119954) and the Roche Research Foundation
(Basel) for generous financial support. We thank Dr. S. R. Dubbaka for
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Keywords: allylation · ene reaction · palladium · sulfonyl
chlorides · umpolung
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Received: March 19, 2010
Published online: July 19, 2010
8988
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