Rhodium-catalysed arylation of aldehydes with arylstannanes

Article abstract of DOI:10.1039/a704108j

Aryltrimethylstannanes react with aldehydes in the presence of a catalytic amount of a cationic rhodium complex, [Rh(cod)(MeCN)₂]BF₄, affording the corresponding arylated secondary alcohols in good yields.

Full text of DOI:10.1039/a704108j

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Rhodium-catalysed arylation of aldehydes with arylstannanes
Shuichi Oi,* Mitsutoshi Moro and Yoshio Inoue
Department of Materials Chemistry, Graduate School of Engineering, Tohoku University, Sendai 980-77, Japan
[
Rh(cod)(MeCN)2]BF4
2 mol%)
Aryltrimethylstannanes react with aldehydes in the presence
of a catalytic amount of a cationic rhodium complex,
(
Ar
R
ArSnR′3 + RCHO
(1)
[
Rh(cod)(MeCN)
2
]BF
4
, affording the corresponding ary-
THF, 60 °C
OH
lated secondary alcohols in good yields.
1
2
3
The addition of organometallic reagents to aldehydes has been
the general method for the synthesis of secondary alcohols.
Among these reagents, organolithium and organomagnesium
[Rh(cod)(MeCN)
dried THF was stirred at 60 °C for an appropriate period of time
under N atmosphere in a sealed Schlenk tube. The reaction was
monitored by TLC. The reaction was quenched by adding a
small amount of water and then stirred for 1 h. After the solvent
was removed in vacuo, the product was isolated by silica gel
column chromatography.
The results are summarized in Table 1. The arylation of
benzaldehyde with trimethylphenylstannane proceeded
smoothly in the presence of 2 mol% cationic rhodium complex
2 4
]BF (cod = cycloocta-1,5-diene) in 1 ml of
(
Grignard reagent) compounds are recognized to be the most
versatile. However, limitations to their use arise from the very
nature of the reagents, namely, their extraordinary reactivity as
nucleophiles and bases. This feature often gives rise to
undesired reactions in the synthesis of multifunctional com-
pounds such as natural products. In order to realize che-
moselective addition to aldehydes, various organometallic
2
1
reagents have been investigated. Nozaki and Hiyama and
2
Kishi reported the addition of organochromium compounds to
aldehydes in the presence of a nickel catalyst. Although this
reaction is highly chemoselective and displays wide compati-
bility with the functional groups in both reaction partners, a
large excess (200–1600 mol%) of chromium salt is required.
The allylation of aldehydes with allylstannanes promoted by a
Lewis acid is one of the most promising reactions and has been
applied successfully in organic systhesis.3 Recently, this
allylation was reported to be also catalysed by transition metal
2 4
[Rh(cod)(MeCN) ]BF , affording diphenylmethanol in 85%
isolated yield (entry 1). NMR examination of the reaction
mixture prior to quenching the reaction by adding water
indicated the formation of the corresponding stannyl ether.
Therefore, the hydrolysis of the stannyl ether must take place
during the work-up. Addition of phosphine ligands such as PPh
to [Rh(cod)(MeCN) ]BF inhibited the reaction. Neutral rho-
dium complexes such as RhCl(PPh and [RhCl(cod)] did not
promote the reaction, nor did the traditional Lewis acids like
TiCl and BF ·OEt The employment of tributyl-
3
2
4
3
)
3
2
4
5
complexes such as those of rhodium, palladium and platinum.
There is, however, no report on the addition of other
4
3
2
.
6
organostannanes to aldehydes except 1-carboranylstannane, a
phenylstannane and tetraphenylstannane instead of trimethyl-
phenylstannane gave diphenylmethanol in lower chemical
yields of 65 and 17%, respectively (entries 2 and 3). The
reaction of p-fluorophenyltrimethylstannane and p-methoxy-
phenyltrimethylstannane with benzaldehyde proceeded
smoothly, affording the corresponding diarylmethanols in good
very special agent. We wish to report here a novel, highly
chemoselective arylation reaction of aldehydes with arylstan-
nanes catalysed by a cationic rhodium complex [eqn. (1)].
The general procedure is as follows. A mixture of 1.2 mmol
of arylstannane 1, 1.0 mmol of aldehyde 2 and 0.02 mmol of
Table 1 Arylation reaction of aldehydes with arylstannanes catalysed by [Rh(cod)(MeCN)
2
]BF a
4
Reaction
conditions
Entry
Arylstannane 1
Aldehyde 2
T/°C t/h
Yield (%)b
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
PhSnMe
PhSnBu
Ph Sn
p-FC
p-MeOC
3
PhCHO
PhCHO
PhCHO
PhCHO
PhCHO
60
60
60 20
60
60
60 24
60 24
60
60
60
60
60
60 20
60 20
60 20
60 24
5
5
85 (87)
(65)
(17)
88
91
85
87
91
96
96
3
4
6
H
4
SnMe
SnMe
3
2
2
6
H
4
3
PhSnMe
PhSnMe
PhSnMe
PhSnMe
PhSnMe
PhSnMe
PhSnMe
PhSnMe
PhSnMe
PhSnMe
PhSnMe
3
p-MeOC
p-MeC
p-ClC
p-MeC(O)C
p-MeOC(O)C
p-(NO )C CHO
Furfural
11CHO
11CHO
CHO
Cyclohexanone
6
H
4
CHO
CHO
CHO
3
6
H
4
3
3
3
3
3
3
3
3
3
6
H
4
5
5
5
5
5
6
H
4
CHO
CHO
1
1
1
1
1
1
1
6
H
4
2
6
H
4
94
91
c
C
5
H
34 (40)
d
6
c-C H
40
54
e
4
tert-C H
9
29
a
atmosphere. b Isolated yield based
A mixture of 1 (1.2 mmol), 2 (1.0 mmol) and [Rh(cod)(MeCN)
2
]BF
4
(0.02 mmol) in THF (1 ml) was stirred under N
2
on 2. Values in parentheses were determined by GC. c Ester 4a (28%) was formed concomitantly. Ester 4b (36%) was formed concomitantly. Ester 4c
d
e
(8%) was formed concomitantly.
Chem. Commun., 1997
1621

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yields (entries 4 and 5). The reaction of trimethylphenyl-
stannane with substituted benzaldehydes and furfural also
proceeded smoothly, affording the corresponding diarylme-
thanol in good to excellent yields (entries 6 to 12). It is noted
that the reaction was highly chemoselective, since other
electrophilic functional groups in 2 such as the acetyl,
methoxycarbonyl and nitro groups remained intact (entries 9, 10
and 11). The reactions of trimethylphenylstannane with ali-
phatic aldehydes, i.e. hexanal, cyclohexanecarboxaldehyde and
trimethylacetaldehyde, afforded the corresponding alcohols in
lower yields of 34, 40 and 54%, respectively (entries 13 to 15).
In these cases, esters 4a, 4b and 4c were formed as by-products
R
Ar
O
Ar SnMe3
SnMe3
Rh+
1
7
Me3Sn+
Me3Sn+
R
Ar
O
Rh
6
Rh Ar
5
R
Ph
R
H
O
R
O
2
O
4
a R = C5H11
b R = c-C6H11
c R = But
Scheme 1
Scheme 1. The transmetallation of the cationic rhodium
complex with 1 would produce the arylrhodium intermediate 5.
Then, addition of 5 to an aldehyde would occur to afford a
rhodium alkoxide complex 6, which would afford the stannyl
in 28 (0.14 mmol), 36 (0.18 mmol) and 8% (0.04 mmol) yield,
respectively. On the contrary, the reactions of trimethylphenyl-
stannane with ketones, i.e. acetophenone and heptan-2-one, did
not take place at all under similar conditions. The reaction with
cyclohexanone proceeded sluggishly, affording the correspond-
ing alcohol in 29% yield (entry 16). To ensure the chem-
oselectivity of the reaction toward aldehyde and ketone, a
competitive reaction of benzaldehyde (1 mmol) and cyclohex-
anone (1 mmol) with trimethylphenylstannane (1 mmol) was
carried out at 60 °C for 5 h. The yield of diphenylmethanol was
3
ether 7. The presence of PPh inhibited the reaction. This
observation is in accord with that reported by Hegedus where
alkyl- and aryl-rhodium(i) phosphine complexes prepared on
the action of Grignard or organolithium reagents on the
corresponding chlororhodium(i) complexes are unreactive to
benzaldehyde.10 Thus a phosphine-free phenylrhodium species
is responsible for this reaction. The mechanism for the
formation of the ester 4 would involve the insertion of another
aldehyde 2 into the Rh–O bond of 6. A similar mechanism was
proposed by Slough in the Tishchenko-type disproportionation
of aldehydes catalysed by rhodium complexes.11
The reaction reported herein represents a new method for
highly chemoselective arylation of aldehydes with aryl-
trimethylstannanes under neutral conditions using a catalytic
amount of a cationic rhodium complex. Further work is now in
progress to investigate the full scope of this reaction.
7
9% and that of 1-phenylcyclohexanol was only 4%, indicating
that the addition of trimethylphenylstannane to benzaldehyde
occurred preferentially.
To gain information on the reaction mechanism, the re-
activity of [Rh(cod)(MeCN)
2
]BF
4
toward benzaldehyde was
studied. However, the cationic rhodium complex did not show
any indication of a reaction with an equimolar amount of
benzaldehyde in THF. The interaction of the rhodium complex
with trimethylphenylstannane 1a was then investigated. When
0
2 4
.1 mmol of [Rh(cod)(MeCN) ]BF was treated with 1.0 equiv.
of 1a in 5.0 ml of THF at 25 °C for 20 h followed by quenching
the reaction with water, the stannane 1a was consumed
completely, affording benzene (44% yield) and a trace amount
Footnote and References
*
E-mail: oishu@aporg.che.tohoku.ac.jp
1
Y. Okude, S. Hirano, T. Hiyama and H. Nozaki, J. Am. Chem. Soc.,
of biphenyl. On quenching the reaction with D
O, the benzene formed was not deuteriated. On the other
hand, 78% of the yielded benzene (62% yield) was deuteriated
on carrying out the reaction in the presence of 1.0 mmol of D O.
2
O instead of
1
977, 99, 3179; T. Hiyama, K. Kimura and H. Nozaki, Tetrahedron
H
2
Lett., 1981, 22, 1037; K. Takai, K. Kimura, T. Kuroda, T. Hiyama and
H. Nozaki, Tetrahedron Lett., 1983, 24, 5281; K. Takai, T. Kuroda,
S. Nakatsukasa, K. Oshima and H. Nozaki, Tetrahedron Lett., 1985, 26,
2
A control experiment confirmed that the stannane 1a was inert
to water. These results indicate the generation of a water-labile
species from [Rh(cod)(MeCN) ]BF and the stannane 1a,
2 4
which we attribute to an unstable phenylrhodium species that
should decompose rapidly to give benzene. Actually, the
reaction of [Rh(cod)(MeCN) ]BF with 1.0 equiv. of 1a in the
2 4
presence of 2.0 equiv. of styrene gave trans-stilbene in 49%
yield, which would be formed by a Heck-type reaction between
the phenylrhodium species and the styrene. We tried in vain to
5
585; K. Takai, M. Tagashira, T. Kuroda, K. Oshima, K. Uchimoto and
H. Nozaki, J. Am. Chem. Soc., 1986, 108, 6048.
2 H. Jin, J. Uenishi, W. J. Christ and Y. Kishi, J. Am. Chem. Soc., 1986,
108, 5644.
3 Review: Y. Yamamoto and N. Asao, Chem. Rev., 1993, 93, 2207.
4
5
J. M. Nuss and R. A. Rennels, Chem. Lett., 1993, 197.
H. Nakamura, N. Asao and Y. Yamamoto, J. Chem. Soc., Chem.
Commun., 1995, 1273; H. Nakamura, H. Iwama and Y. Yamamoto,
J. Am. Chem. Soc., 1996, 118, 6641.
7
6
7
H. Nakamura, N. Sadayori, M. Sekido and Y. Yamamoto, J. Chem. Soc.,
Chem. Commun., 1994, 2581.
R. F. Heck, J. Am. Chem. Soc., 1968, 90, 5518.
1
13
detect a peak corresponding to the species by H and C NMR
measurement of the reaction performed in [ H ]THF. There are
8
2
several reports on the transmetallation between transition
metals and arylstannanes to give arylmetal species as are shown
in the Stille coupling reaction. It was also reported that a
8 J. K. Stille, Angew. Chem., Int. Ed. Engl., 1986, 25, 508.
9 W. Keim, J. Organomet. Chem., 1969, 19, 161.
10 L. S. Hegedus, P. M. Kendall, S. M. Lo and J. R. Sheats, J. Am. Chem.
Soc., 1975, 97, 5448.
8
3 2
phenylrhodium complex, RhPh(CO)(PPh ) , thermally decom-
9
11 G. A. Slough, J. R. Ashbaugh and L. A. Zannoni, Organometallics,
poses into benzene,biphenyl and benzophenone.
1
994, 13, 3587.
The presumed reaction pathway for the novel arylation
reaction of aldehydes 2 with arylstannanes 1 is shown in
Received in Cambridge, UK, 12th June 1997; 7/04108J
1622
Chem. Commun., 1997