Traceless chelation-controlled rhodium-catalyzed intermolecular alkene and alkyne hydroacylation

Article abstract of DOI:10.1002/chem.201204056

A new functional-group tolerant, rhodium-catalyzed, sulfide-reduction process is combined with rhodium-catalyzed chelation-controlled hydroacylation reactions to give a traceless hydroacylation protocol. Aryl- and alkenyl aldehydes can be combined with both alkenes, alkynes and allenes to give traceless products in high yields. A preliminary mechanistic proposal is also presented. Traceless catalysis: The powerful combination of a chelation-controlled hydroacylation process and a new rhodium-catalyzed sulfide reduction gave the products of traceless hydroacylation. Aryl- and alkenyl aldehydes can be combined with alkenes, alkynes, and allenes to deliver traceless products in high yields (see scheme). Copyright

Full text of DOI:10.1002/chem.201204056

FULL PAPER
DOI: 10.1002/chem.201204056
Traceless Chelation-Controlled Rhodium-Catalyzed Intermolecular Alkene
and Alkyne Hydroacylation
Joel F. Hooper, Rowan D. Young, Andrew S. Weller, and Michael C. Willis*[a]
Abstract: A new functional-group tolerant, rhodium-catalyzed, sulfide-reduction
process is combined with rhodium-catalyzed chelation-controlled hydroacylation
reactions to give a traceless hydroacylation protocol. Aryl- and alkenyl aldehydes
can be combined with both alkenes, alkynes and allenes to give traceless products
in high yields. A preliminary mechanistic proposal is also presented.
Keywords: acylation · rhodium ·
sulfide reduction · synthetic meth-
ods · tandem reactions
Introduction
The use of chelation-control strategies has contributed enor-
mously to the progress of intermolecular alkene and alkyne
hydroacylation reactions as synthetically useful transforma-
tions.[1] For example, efficient reactions have been devel-
oped that rely on C-,[2] N-,[3] O-,[4] S-[5] or P-coordinating
substituents,[6] with examples of the coordinating group posi-
tioned on either the aldehyde or the alkene/alkyne reaction
component.[7] The resultant chelated motif is generally in-
voked as stabilizing key acyl–metal intermediates (Scheme
1). These reactions now encompass a wide substrate scope
and have allowed both enantioselective[7c,8] and regioselec-
tive[9] variants to be developed. An inherent feature of che-
Scheme 1. Chelation-controlled and traceless chelation-controlled alkene/
alkyne hydroacylation.
lation-controlled reactions is that the chelating group, which
is necessarily present in the starting materials to ensure fa-
vourable reACHTUNGTRENNUNGactivity, is also present in the product molecules.
Derivatization of these controlling groups can provide op-
Results and Discussion
portunities for further functionalization of the products,[4-
d,5a,10]
but if an unadorned molecule is required, they repre-
The first task in addressing the development of a traceless
chelation-controlled hydroacylation protocol was to identify
a suitable method of efficiently cleaving the original coordi-
nating group. Based on the advances our laboratory has
made in the use of b-S-chelating aldehydes in alkene and
alkyne hydroacylation reactions,[5] this chelation motif
seemed ideal. However, established methods for the reduc-
tive cleavage of simple aryl methyl sulfides to the parent
arene are largely limited to those based on Raney nickel or
other stoichiometric metal-reducing agents.[12] Given the
poor functional group tolerance that such a reductive step
would provide, we explored the use of milder reaction con-
ditions by using silane reductants. Silane reductions of aryl
methyl sulfides have recently been reported by using nickel
and palladium catalysts,[13] although application of both of
these methods to our hydroacylation products resulted in
the formation of mixtures of ketone hydrosilylation and silyl
enol ether products (see the Supporting Information).[14]
Based on our recent success in the activation of aryl methyl
sulfides with the RhI catalyst A (Table 1) and subsequent
application to the development of a new alkyne carbothiola-
sent a limitation of the strategy. Although a number of ex-
amples of successful non-chelation-controlled intermolecular
hydroacylation reactions is known, they generally require
specific substrate combinations or harsh reaction condi-
tions.[11] Herein, we document the development of the first
traceless chelation-controlled intermolecular hydroacylation
protocol, a pro
controlled approach – broad substrate scope and mild re-
ACHTUNGTRENNUNGaction conditions – but allows the formation of products
ACHTUNGTRENNUNGcess which enjoys the benefits of a chelation-
lacking a superfluous coordinating group.
[a] Dr. J. F. Hooper, Dr. R. D. Young, Prof. A. S. Weller, Dr. M. C. Willis
Department of Chemistry
University of Oxford, Chemistry Research Laboratory
Mansfield Road, Oxford, OX1 3TA (U.K.)
Fax : (+44)1865-285002
E-mail: michael.willis@chem.ox.ac.uk
Supporting information for this article contains full characterisation
data for organic and inorganic products, X-ray crystallography and ki-
netic plots and is available on the WWW under http://dx.doi.org/
10.1002/chem.201204056.
Chem. Eur. J. 2013, 19, 3125 – 3130
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3125

Table 1. Catalyst evaluation for sulfide reduction by using ketone 1.[a]
Table 2. Optimization of reducing agents for sulfide 1.[a]
Catalyst
T [8C] Conversion[b]
1
2
3
4
5
[Rh
[Rh
N
G
N
80
80
80
25
33%
15%
Catalyst
Reductant
T [8C]
Conversion[b]
[Rh(Cy2PCH2PCy2)
R
N
100% (50%)[c]
100% (73%)[c]
<10%
1
2
3
4
C (5 mol%)
C (5 mol%)
C (5 mol%)
C (5 mol%)
C (5 mol%)
C (1 mol%)
E (1 mol%)
H2 (1 atm)
Ph2SiH2
PhSiH3
PMHS
G
80
25
25
25
25
25
25
<10%
E
complex mix
complex mix
80%
N
[BArF4] D 80
3ACHTUNGTRENNUNG
[a] ArF =3,5-C6H (CF3)2. [b] Determined by 1H NMR analysis of the
crude reaction mixture. [c] Isolated yields in parenthesis. [d] Precatalyst
activated with H2. nbd=norbornadiene.
5[c]
6[d]
7[e]
100%
A
100% (95%)[f]
100%
AHCTUNGTRENNUNG
3ACTHNUTRGNEUNG
[a] ArF =3,5-C6H (CF3)2. [b] Determined by 1H NMR analysis of the
crude reaction mixture. [c] Complete in 15 min. [d] Complete in 1 h.
[e] Complete in 30 min. [f] Isolated yield in parenthesis.
tion process, we decided to investigate the use of rhodium
catalysis for the selective reduction of methyl sulfides.[10] An
important goal in exploring this chemistry was to develop a
sulfide-reduction process that was tolerant of potentially re-
active, synthetically useful, functional groups, such as ke-
tones, esters and halides.
for further studies; as although both C and E[17] are bench-
stable pre-catalysts, complex C can be conveniently pre-
pared from commercially available materials.
The aryl ketone 1 was selected as a suitable substrate to
explore the reduction chemistry, and a number of RhI cata-
lysts were evaluated employing Et3SiH as the reducing
agent (Table 1). Although the (2-diphenylphosphinophenyl)-
Having established mild and efficient conditions for the
reductive cleavage of an aryl methyl sulfide in the presence
of an ortho-ketone group, the role of directing groups in
À
promoting C S bond cleavage was investigated (Table 3).
A
Substrates with an ortho-carbonyl group were well tolerated,
with alkyl- and aryl-ketones (4a–c), and a Weinreb amide
version to reduced product 2 (Table 1, entry 1), complex C
was quickly identified,[15] featuring the small-bite-angle
ligand bis(dicyclohexylphosphanyl)methane (Cy2PCH2PCy2),
as an active catalyst for this reaction. Performing this reduc-
tion at 808C resulted in significant hydrosilylation of the
ketone (Table 1, entry 3), although this could be attenuated
by reducing the temperature of the reaction (Table 1,
entry 4). Under these conditions, complete consumption of
the starting material was observed, and the desired product
was isolated in 73% yield.
À
(4d) all undergoing selective C S cleavage. Heterocyclic di-
recting groups could also be employed, with a pyridyl group
promoting the chemoselective cleavage of an ortho-SMe
group in the presence of a para-sulfide (4e). A substrate
containing an ortho-oxazoline group was also effective,
giving phenyl-oxazoline (4 f). The thiophene ketone 4g
Table 3. Directing group effects on aryl sulfide reduction.[a]
Next, attention was turned to identifying the optimum re-
ducing agent for this reaction (Table 2). Performing the re-
action under an atmosphere of H2 gas resulted in only par-
ACHTUNGTRENNUNGtial reduction of the ketone, and no observed SMe cleavage
(Table 2, entry 1). The use of phenyl-substituted silanes gave
complex mixtures of products, resulting from non-selective
reductive cleavage of the SMe group and ketone hydrosi-
ACHTUNGTRENNUNGlylation (Table 2, entries 2 and 3). We were pleased to see
that polymethylhydrosiloxane (PMHS), an inexpensive by-
product of the silicone industry,[16] was an effective reducing
agent for this reaction (Table 2, entry 4). However, optimal
results were obtained when (EtO)3SiH was employed, re-
sulting in complete conversion in only 15 min when 5 mol%
of catalyst C was used (Table 2, entry 5). The catalyst load-
ing could be reduced to 1 mol%, which gave complete con-
version and a 95% isolated yield of ketone 2 in one hour
(Table 2, entry 6). Complex E, containing isopropyl substitu-
ents on the phosphorus atoms, displayed even greater re-
ACHTUNGTRENNUNG
[a] Conditions: 3 (1.0 equiv), catalyst (5 mol%), (EtO)3SiH (2.0 equiv).
Isolated yields. [b] Conversion from H NMR spectroscopy.
1
3126
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 3125 – 3130

Chelation-Controlled Rhodium-Catalyzed Hydroacylation
FULL PAPER
Table 4. Traceless chelation-controlled hydroacylation.[a]
could also be prepared in good yield, showing the compati-
bility of this reaction with heterocyclic scaffolds. However,
substrate 3h with a benzylic amine was unreactive. Substrate
3i, featuring a para-disposed acyl group, was also unreactive,
thus confirming the requirement for ortho-coordination.
We have previously reported that complex C is a highly
active catalyst for the sulfide-directed hydroacylation of al-
kenes and alkynes.[15] This raised the exciting possibility of
performing hydroacylation reactions, in which the SMe
À
group would act as a directing group for aldehyde C H acti-
À
vation, followed by reductive cleavage of the C S bond with
the same catalyst. This reaction would give ketone products,
in which the thiomethyl group acts as a traceless directing
group. Based on the ease with which the thiomethyl sub-
stituent can be introduced, by using simple SNAr chemistry,
this combination would provide an attractive route to
ketone products. We tested this concept by subjecting the al-
dehyde 5a to hydroacylation conditions, employing
10 mol% of catalyst C and 1-octene (Table 4). After two
hours at 808C, the mixture was cooled to room temperature,
and (EtO)3SiH was added. After stirring overnight, we were
pleased to find that the ketone 6a could be isolated in 87%
yield. The alkene component of this reaction could be easily
varied, and very good functional group tolerance was ob-
served. For example, products featuring ester (6b), acetal
(6c) and sulfonamide (6d) groups were all delivered in good
yields. This reaction is also highly compatible with both
alkyl- (6e) and aryl-halides (6 f), allowing for the possibility
of further functionalization of the products. Variation of the
aldehyde component of the reaction was also possible. The
dimethoxy aldehyde 5g gave the ketone product in 84%
yield, and an aldehyde with both ortho- and para-SMe
groups gave the ortho-reduced product in good yield. Pleas-
ingly, the aldehyde scope was not limited to aromatic sub-
strates, as the cycloalkenyl aldehyde 5i delivered the corre-
sponding a,b-unsaturated ketone. The stability of the enone
product 6i suggested that the products of traceless alkyne
hydroacylation could also be accessed. By using the iPr-sub-
stituted catalyst E, recently reported as a highly active cata-
lyst for alkyne hydroacylation,[17] bulky terminal alkynes, as
well as an internal alkyne could be employed, delivering
enones 6j and 6k in excellent yields. Bis-enones were also
accessible (6l). Catalyst E was also used for the hydroacyla-
tion of butyl vinyl ether, which proceeds with high branched
selectivity to give the a-substituted ketone 6m. Finally, the
hydroacylation of an allene could be achieved with catalyst
C, which gave the b,g-unsaturated ketone 6n following
silane reduction.
[a] Conditions
5 (1.0 equiv), alkene/alkyne (1.5 equiv), complex C
(10 mol%), (EtO)3SiH (2.0 equiv), Isolated yields. [b] Complex E was
used as catalyst.
complex
D
(featuring the small bite-angle di-
AHCTUNGTREG(NNUN tBu)phosphine) can catalyse the hydroacylation of unacti-
vated alkenes at as low as 0.1% catalyst loading.[15] The
most efficient catalyst for the aryl sulfide reduction step is
complex E,[17] which can efficiently deliver the reduced com-
pound by using only 0.5 mol% loading (Scheme 2). By com-
bining these two catalysts into a one-pot tandem reaction,
the traceless hydroacylation product 2 could be isolated in
82% yield, although employing only 0.8 mol% Rh in total
(Scheme 2). This represents an efficient method for the syn-
thesis of these valuable ketone products. These two proce-
dures, involving either a single catalyst at higher loading, or
two separate catalysts at low loading, are complementary,
and allow the choice of either catalyst loading, or the con-
venience of a simplified reaction procedure, to be the para-
mount consideration.
The use of catalyst C represents a convenient method for
tandem hydroacylation/sulfide reduction, because this cata-
lyst is active in both steps, bench stable and easily prepared
from commercially available materials. However, the use of
the relatively high catalyst loading of 10 mol% for this
tandem reaction is not ideal. The amount of catalyst needed
can be dramatically reduced if two separate catalysts are
employed, each of which have been optimised for the indi-
vidual steps of the process. We have previously shown that
We have probed the mechanism of the sulfide reduction
process employing precatalyst C,[18] with a combination of
Chem. Eur. J. 2013, 19, 3125 – 3130
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3127

M. C. Willis et al.
of the 2-pyridyl group (Scheme 3 and the Supporting Infor-
mation). In compound 7, coordination of the ortho-ketone
likely occurs to retain an 18-electron count at each Rh. The
NMR data for 7 and 8 are similar, and 8 also showed a
[M2]2+ parent ion in the ESI-MS (m/z=758.27, calcd
758.26). Both compounds 7 and 8 are essentially inactive in
catalysis, showing that once formed they represent a deacti-
vation pathway for this process in CH2Cl2 (or C2H4Cl2). An
active species is formed upon addition of 3a to
[Rh(Cy2PCH2PCy2)
[Rh(Cy2PCH2PCy2)(SMe)
AHCTUNGTRENNUNG
[BArF ] (10), rather than the dimer. This reaction is rapid
N
E
(9)[15]
to
form
4
Scheme 2. Reduction and traceless HA by using low catalyst loadings.
G
ACHTUNGTRENNUNG
4
stoichiometric and catalytic experiments by considering the
suggesting that dissociation of fluorobenzene is the limiting
À
two likely pathways: C S bond cleavage followed by addi-
factor in the reaction of C with 3a in CH2Cl2. NMR data
suggest that 10 is in rapid equilibrium with 9/3a at room
tion of silane (cycle A)[13a] or silane addition and then C S
À
[10,19]
[10,19]
À
À
cleavage (cycle B; Scheme 3). Both C S bond cleavage
temperature through reversible C S bond cleavage,
which can be arrested at À808C (Keq ꢀ3 in favour of 10).
Addition of excess MeCN to this mixture resulted in the
near-quantitative conversion to 9, and ESI-MS of 10 showed
it to be monomeric.
Addition of excess final product acetophenone (4a) to C
resulted in the quantitative (as determined by 31P{1H} NMR
spectroscopy)
formation
of
the
h6-adduct
[Rh(Cy2PCH2PCy2)
G
ACHTUNGTRENNUNG
4
over in catalysis (10 mol%, 258C, 100% conversion) at a
similar rate to that observed by using C (ToFꢀ60 hÀ1), con-
sistent with their similar structures and a requirement to dis-
sociate the bound arene prior to catalysis. However, com-
pounds 9 and 10 act considerably faster when used in cataly-
sis (100% conversion, ToF at least 600 hÀ1), consistent with
both the absence of bound arene and their monomeric struc-
tures (i.e., 10). In the absence of MeCN under catalytic con-
ditions (10 mol% C), substrate or product (e.g., 3a or 4a)
presumably coordinate hindering dimerization to 7, and
under these conditions 3e also turns over. The cycle A is
completed by addition of HSi
ACHTUNGRTEN(NUNG OEt)3 to 10, which shows the
À
elimination of 4a (i.e., 11 is formed) and MeS SiACHTUNGTRENNUNG(OEt)3.
This process presumably occurs either by sigma-bond meta-
thesis through an h2-silane,[22] for example, F, or oxidative
addition to give a RhV species.[23] Intermediates, such as F,
Scheme 3. Species observed or implicated on the catalytic cycle. In
À
CH2Cl2 solvent, L=CH2Cl2 or agostic interaction.
have recently been invoked in reactivity of C S bonds with
silanes.[13a,24] Interestingly, addition of 3a to pre-catalyst D
only afforded the RhI k2-S,O adduct[15] with no C S activa-
À
and oxidative addition of silanes[20] to Rh centres are estab-
lished. Addition of 3a to complex C (CH2Cl2 solution, 1:1)
resulted in the slow consumption of C following first-order
tion observed, consistent with the lack of conversion in cat-
alysis (Table 1). Similarly, the lack of reactivity of the DPE-
phos complex A might suggest k3-P,O,P coordination[10,25]
blocking the vacant site necessary for silane activation (i.e.,
F).
III
1
kinetics (t = =30Æ5 min) and the formation of a new Rh
2
species
[Rh(Cy2PCH2PCy2)ACHTUNTGREG(NUNN m-SMe)ACHTUNRTEGN{GNUN s,k-C6H4CAHTNUGTRNEUN(GN OCMe)}]2-
A
To probe the alternative cycle B, addition of excess[26]
4
were unable to resolve whether 7 is a monomer or dimer in
CH2Cl2 solution, but ESI-MS[21] clearly showed a [M2]2+
parent ion (m/z=677.27, calcd 677.26). Complex 7 is formed
as an intractable oil on attempted recrystallization, but the
closely related complex incorporating pyridyl 3e (Table 3)
did afford crystalline material 8 suitable for X-ray diffrac-
tion studies, which showed a dimeric motif with bridging
HSi
ACHTUGNERTN(NUNG OEt)3 to C (CH2Cl2 solution) resulted in a slow (4 h)
reaction to form a RhIII complex tentatively characterised as
[trans-Rh(Cy2PCH2PCy2)(H)(Si
A
N
4
agostic C H, CH2Cl2 or h -silane[20,22]). H
{31P} NMR experi-
2
1
À
ments (À808C, see the Supporting Information) argue
against a dimeric motif with bridging hydride ligands, be-
cause a single hydride resonance is observed at d À7.90 as a
À
SMe groups, arising from C S activation and coordination
doublet [JACTHNGUETRNNU(G RhH) 15 Hz], which resolves into a virtual quar-
3128
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 3125 – 3130

Chelation-Controlled Rhodium-Catalyzed Hydroacylation
FULL PAPER
tet in the 1H NMR spectrum. Complex 12 is fluxional at
d) M. von Delius, C. M. Le, VM. Dong, J. Am. Chem. Soc. 2012,
134, 15022.
room temperature. Addition of 3a/HSiACTHNUTRGENUG(N OEt)3 to this com-
[5] For selected examples, see: a) M. C. Willis, S. J. McNally, P. J. Bes-
wick, Angew. Chem. 2004, 116, 344; Angew. Chem. Int. Ed. 2004, 43,
340; b) M. C. Willis, H. E. Randell-Sly, R. L. Woodward, G. S.
Currie, Org. Lett. 2005, 7, 2249; c) M. C. Willis, R. L. Woodward, J.
Am. Chem. Soc. 2005, 127, 18012; d) M. C. Willis, H. E. Randell-Sly,
R. L. Woodward, S. J. McNally, G. S. Currie, J. Org. Chem. 2006, 71,
5291; e) G. L. Moxham, H. E. Randell-Sly, S. K. Brayshaw, R. L.
Woodward, A. S. Weller, M. C. Willis, Angew. Chem. 2006, 118,
7780; Angew. Chem. Int. Ed. 2006, 45, 7618; f) J. D. Osborne, M. C.
Willis, Chem. Commun. 2008, 5025; g) P. Lenden, D. A. Entwistle,
M. C. Willis, Angew. Chem. Int. Ed. 2011, 50, 10657; h) P. Lenden,
P. M. Ylioja, C. Gonzꢁlez-Rodrꢂguez, D. A. Entwistle, M. C. Willis,
Green Chem. 2011, 13, 1980.
[6] H. Lee, C. H. Jun, Bull. Korean Chem. Soc. 1995, 16, 66.
[7] a) K. Tanaka, Y. Shibata, T. Suda, Y. Hagiwara, M. Hirano, Org.
Lett. 2007, 9, 1215; b) Y. Inui, M. Tanaka, M. Imai, K. Tanaka, H.
Suemune, Chem. Pharm. Bull. 2009, 57, 1158; c) M. C. Coulter,
K. G. M. Kou, B. Galligan, V. M. Dong, J. Am. Chem. Soc. 2010,
132, 16330.
[8] a) R. T. Stemmler, C. Bolm, Adv. Synth. Catal. 2007, 349, 1185;
b) J. D. Osborne, H. E. Randell-Sly, G. S. Currie, A. R. Cowley,
M. C. Willis, J. Am. Chem. Soc. 2008, 130, 17232; c) Y. Shibata, K.
Tanaka, J. Am. Chem. Soc. 2009, 131, 12552; d) D. T. H. Phan,
K. G. M. Kou, V. M. Dong, J. Am. Chem. Soc. 2010, 132, 16354;
e) C. Gonzꢁlez-Rodrꢂguez, S. R. Parsons, A. L. Thompson, M. C.
Willis, Chem. Eur. J. 2010, 16, 10950; f) C. Gonzꢁlez-Rodrꢂguez,
M. C. Willis, Pure Appl. Chem. 2011, 83, 577.
[9] a) C.-H. Jun, H. Lee, J.-B. Hong, B.-I. Kwon, Angew. Chem. 2002,
114, 2250; Angew. Chem. Int. Ed. 2002, 41, 2146; b) S. Omura, T. Fu-
kuyama, J. Horiguchi, Y. Murakami, I. Ryu, J. Am. Chem. Soc. 2008,
130, 14094; c) F. Shibahara, J. F. Bower, M. J. Krische, J. Am. Chem.
Soc. 2008, 130, 14120; d) C. Gonzꢁlez-Rodrꢂguez, R. J. Pawley, A. B.
Chaplin, A. L. Thompson, A. S. Weller, M. C. Willis, Angew. Chem.
2011, 123, 5240; Angew. Chem. Int. Ed. 2011, 50, 5134; e) H.-J.
Zhang, C. Bolm, Org. Lett. 2011, 13, 3900; f) S.-J. Poingdestre, J. D.
Goodacre, A. S. Weller, M. C. Willis, Chem. Commun. 2012, 48,
6354.
plex resulted in turnover (10 mol%, ToFꢀ300 hÀ1) showing
that 12 lies on, or is at least connected to, the productive
cycle. Addition of one equivalent of 3a to 12 resulted in
À
rapid formation of 11 and MeS SiACHTNUGTRENUNG(OEt)3. Interestingly, ad-
dition of HSiACHTUNGTRENNUNG(OEt)3 to 9 occurred only very slowly, in con-
trast to the addition of 3a to 9. Unfortunately, our data
herein do not allow us to discriminate between cycles A and
B in CH2Cl2 solvent, and it is possible that both are operat-
ing in parallel. However, in the presence of excess MeCN
(i.e., 9 as the precatalyst) it is likely that pathway A mainly
operates, because addition of HSi
ACHTUNGTRENNUNG
than catalysis starting from 9/3a and HSiACHTUNGTRENNNUG
addition of MeCN to 12 resulted in the formation of the
non-fluxional MeCN adduct, that is, L=MeCN (see the
Supporting Information), which is inactive in catalysis when
using 3a.
Immediately at the end of catalysis using C, unreacted C
(90%) and 11 (10%) were observed, consistent with the
slow (cf turnover) displacement of fluorobenzene by 3a.[27]
The implication of these observations is that the actual
active catalyst concentration is much lower than the load-
ings used. Consistent with this, the MeCN adduct 9 turns
over in catalysis much faster than C.[15]
Conclusion
A new Rh-catalysed silane-mediated sulfide reduction pro-
ACHTUNGTRENNUNGcess, which operates under mild reaction conditions and dis-
plays excellent functional group tolerance, was reported.
When partnered with an initial Rh-catalysed alkene, alkyne
or allene hydroacylation procedure, the overall cascade
process gives the products of traceless chelation-controlled
hydroacylation. This new process uses the mild reaction con-
ditions and has the substrate scope of chelation-mediated
hydroacylation, yet delivers products free of an unwanted
coordinating substituent.
[10] J. F. Hooper, A. B. Chaplin, C. Gonzꢁlez-Rodrꢂguez, A. L. Thomp-
son, A. S. Weller, M. C. Willis, J. Am. Chem. Soc. 2012, 134, 2906.
[11] For a review, see: a) J. C. Leung, M. J. Krische, Chem. Sci. 2012, 3,
2202; Selected examples: b) T. B. Marder, D. C. Roe, D. Milstein,
Organometallics 1988, 7, 1451; c) T. Kondo, M. Akazome, Y. Tsuji,
Y. Watanabe, J. Org. Chem. 1990, 55, 1286; d) T. Tsuda, T. Kiyoi, T.
Saegusa, J. Org. Chem. 1990, 55, 2554; e) C. P. Lenges, P. S. White,
M. Brookhart, J. Am. Chem. Soc. 1998, 120, 6965; f) A. H. Roy, C. P.
Lenges, M. Brookhart, J. Am. Chem. Soc. 2007, 129, 2082; g) V. M.
Williams, J. C. Leung, R. L. Patman, M. J. Krische, Tetrahedron
2009, 65, 5024; h) S. Hatanaka, Y. Obora, Y. Ishii, Chem. Eur. J.
2010, 16, 1883.
Acknowledgements
[12] a) For Raney Ni, see: R. Mozingo, D. E. Wolf, S. A. Harris, K. J.
Folkers, J. Am. Chem. Soc. 1943, 65, 1013; b) Al/HgCl2: T. Sugimoto,
N. Nishioka, S. Murata, S. Matsuura, Heterocycles 1987, 26, 2091;
c) Ni- boride: A. Zumbrunn, Synthesis 1998, 1357; d) Zn/HCl: J. J.
Baldwin, E. L. Engelhardt, R. Hirschmann, G. S. Ponticello, J. G. At-
kinson, B. K. Wasson, C. S. Sweet, A. Scriabine, J. Med. Chem. 1980,
23, 65.
This work was supported by the EPSRC. We thank Indrek Pernik for the
synthesis of catalyst E.
[1] a) M. C. Willis, Chem. Rev. 2010, 110, 725; b) C. Jun, E. Jo, C.-H.
Jun, E.-A. Jo, J.-W. Park, Eur. J. Org. Chem. 2007, 1869.
[13] a) N. Barbero, R. Martin, Org. Lett. 2012, 14, 796; b) T. Matsumura,
T. Niwa, M. Nakada, Tetrahedron Lett. 2012, 53, 4313.
[14] C. D. F. Kçnigs, H. F. T. Klare, Y. Ohki, K. Tatsumi, M. Oestreich,
Org. Lett. 2012, 14, 2842.
[15] A. B. Chaplin, J. F. Hooper, A. S. Weller, M. C. Willis, J. Am. Chem.
Soc. 2012, 134, 4885.
[2] C. F. Lochow, R. G. Miller, J. Am. Chem. Soc. 1976, 98, 1281.
[3] For examples, see: a) J. W. Suggs, J. Am. Chem. Soc. 1979, 101, 489;
b) C. H. Jun, J. S. Han, J. B. Kang, S. I. Kim, Bull. Korean Chem.
Soc. 1994, 15, 204; c) C.-H. Jun, H. Lee, J.-B. Hong, J. Org. Chem.
1997, 62, 1200; d) N. R. Vautravers, D. D. Regent, B. Breit, Chem.
Commun. 2011, 47, 6635.
[16] N. J. Lawrence, M. D. Drew, S. M. Bushell, J. Chem. Soc. Perkin
Trans. 1 1999, 3381.
[17] I. Pernik, J. Hooper, A. B. Chaplin, A. S. Weller, M. C. Willis, ACS
Catalysis, 2012, 2, 2779.
[4] For selected examples, see: a) K. Kokubo, K. Matsumasa, M. Miura,
M. Nomura, J. Org. Chem. 1997, 62, 4564; b) M. Imai, M. Tanaka,
K. Tanaka, Y. Yamamoto, N. Imai-Ogata, M. Shimowatari, S.
Nagumo, N. Kawahara, H. Suemune, J. Org. Chem. 2004, 69, 1144;
c) S. R. Parsons, J. F. Hooper, M. C. Willis, Org. Lett. 2011, 13, 998;
[18] Catalyst E was also studied and showed very similar behavior to C.
Chem. Eur. J. 2013, 19, 3125 – 3130
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3129

M. C. Willis et al.
[19] W. D. Jones, Inorg. Chem. 2005, 44, 4475.
[26] An excess of HSi
drocoupling to form [Si
Organomet. Chem. 2004, 51, 1.
[27] With time (2 h post-catalysts) [Rh(Cy2PCH2PCy2)
[BArF4] (13) also grows in, but no evidence for this during, or imme-
ACHTUNGTRENNUNG
[20] J. Y. Corey, J. Braddock-Wilking, Chem. Rev. 1998, 98, 175.
[21] A. T. Lubben, J. S. McIndoe, A. S. Weller, Organometallics 2008, 27,
3303.
[22] S. Lachaize, S. Sabo-Etienne, Eur. J. Inorg. Chem. 2006, 2115.
[23] J. L. McBee, J. Escalada, T. D. Tilley, J. Am. Chem. Soc. 2009, 131,
12703.
ACHTUNGTRENNUNG
À
ACHUTNERGN(NUG MeS SiACHTUNGTRENNUNG(OEt)3)]-
ACHTUNGTRENNUNG
diately after, catalysis was seen. Compound 13 is inactive in cataly-
sis.
[24] H. F. T. Klare, M. Oestreich, J.-i. Ito, H. Nishiyama, Y. Ohki, K. Tat-
sumi, J. Am. Chem. Soc. 2011, 133, 3312.
[25] G. L. Moxham, H. Randell-Sly, S. K. Brayshaw, A. S. Weller, M. C.
Willis, Chem. Eur. J. 2008, 14, 8383.
Received: November 13, 2012
Published online: January 16, 2013
3130
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 3125 – 3130