Synthesis of 1,2-diketones by the transition metal-catalyst-free reaction of α-oxo acid chlorides or oxalyl chloride with organostannanes

Article abstract of DOI:10.1021/jo802814r

(Chemical Equation Presented) The reaction of an α-oxo acid chloride with an organostannane proceeds transition metal-catalyst-free to afford a 1,2-diketone in an excellent yield. In addition, a sequence comprising pretreatment of oxalyl chloride with an

Full text of DOI:10.1021/jo802814r

SCHEME 1. Transition Metal-Catalyst-Free 1,2-Diketone
Synthesis Starting with r-Oxo Acid Chloride and
Organostannane
Synthesis of 1,2-Diketones by the Transition
Metal-Catalyst-Free Reaction of r-Oxo Acid
Chlorides or Oxalyl Chloride with
Organostannanes
Taigo Kashiwabara and Masato Tanaka*
catalyst-free under much milder reaction conditions (rt ∼75 °C,
less than 1 h in most cases). Besides these, when the Sn-C
bond is somehow activated by an R-heteroatom, the cross-
coupling appears to proceed catalyst-free. Thus, the reaction
with (R-sulfonylcyclopropyl)stannane and (R-sulfonylvinyl)-
stannane reagents affords corresponding R-sulfonylcyclopropy
and R-sulfonylvinyl ketones in fair to high yields.8 R-Stan-
nylpyridines and R-stannylpyrimidines are also reactive under
catalyst-free and exceptionally mild conditions toward acyl
chlorides to furnish corresponding heterocyclic ketones.9 How-
ever, similar reactions of R-oxo acyl chlorides with R-stan-
nylpyridines and R-stannylpyrimidines do not afford diketones
selectively, but also form the “mono” ketones, due to concomi-
tant decarbonylation, which is believed to stem from the
participation of R-nitrogen. The only catalyst-free cross-coupling
of simple organostannane compounds appeared quite recently
and disclosed the necessity of harsh conditions (130 °C, up to
90 h) and only moderate yields being obtained.10
During the course of our research on the transition metal-
catalyzed reactions of R-oxo acid chlorides, we have come
accidentally across high-yielding formation of 1,2-diketones in
the reaction with organostannane compounds in the absence of
a transition metal catalyst (Scheme 1), which will be disclosed
in this note. There are quite a few synthetic methodologies for
simple 1,2-diketones (vide infra),11 but synthesis of alkenyl and
alkynyl 1,2-diketones has been very limited.12
Chemical Resources Laboratory, Tokyo Institute of
Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
m.tanaka@res.titech.ac.jp
ReceiVed December 27, 2008
The reaction of an R-oxo acid chloride with an organostan-
nane proceeds transition metal-catalyst-free to afford a 1,2-
diketone in an excellent yield. In addition, a sequence
comprising pretreatment of oxalyl chloride with an orga-
nostannane and a subsequent treatment with another orga-
nostannane also works as a convenient modification.
Electrophilic substitution at an aryl-Sn bond is a well-known
process.1 For instance, the AlCl3-catalyzed reaction of arylstan-
nanes with acid chlorides affords aryl ketones in high yields.2
Ketone synthesis by transition metal-catalyzed cross-coupling
of acid chlorides with organostannanes is also well studied since
the pioneering work by Kosugi-Migita3 and also that by
Stille-Milstein.4 The Stille-Milstein procedure using a pal-
ladium complex catalyst was also applied to the synthesis of
1,2-diketones starting with acyl chlorides and acylstannane
reagents, although the reaction required long heating at high
temperatures, resulting in only moderate yields.5 On the other
hand, one of us reported near-quantitative synthesis of R-oxo
nitriles6 and R-oxo amides7 by the reactions of Bu3Sn-CN and
Me3Sn-CONiPr2 with acid chloride derivatives, which work
In a representative experiment, a toluene solution of phenyl-
2-oxoacetyl chloride 1a and tri-n-butyl(allyl)stannane 2A was
stirred at 110 °C for 3 h. Routine workup of the resulting
mixture, inclusive of treatment with aqueous potassium fluoride
to convert chlorotri-n-butylstannane coproduct to an insoluble
polymeric material, followed by preparative TLC afforded
1-phenylpent-4-ene-1,2-dione 3aA in 96% isolated yield. The
product showed satisfactory spectral data.
Interestingly, when a trial reaction of 1a with 2A (1 equiv)
was run, according to the Migita-Kosugi procedure with
RhCl(PPh3)3 (2.0 mol %) at 80 °C for 3 h, the desired diketone
was not formed in an appreciable yield, and instead, 1-phenyl-
(8) Pohmakotr, M.; Khosavanna, S. Tetrahedron 1993, 49, 6483.
(9) (a) Yamamoto, Y.; Ouchi, H.; Tanaka, T. Chem. Pharm. Bull. 1995, 43,
1028. (b) Yamamoto, Y.; Ouchi, H.; Tanaka, T.; Morita, Y. Heterocycles 1995,
41, 1275.
(10) Silbestri, G. F.; Masson, R. B.; Lockhart, M. T.; Chopa, A. B. J.
Organomet. Chem. 2006, 691, 1520.
(1) (a) Davies, A. G. Organostannane Chemistry; VCH: Weinheim, Germany,
1997; Chapters 4 and 6. (b) Wardell, J. L. In Chemistry of Tin, 2nd ed.; Smith,
P. J., Ed.; Chapman & Hall: London, UK, 1998; Chapter 4 and references cited
therein.
(2) Neumann, W. P.; Hillga¨rtner, H.; Baines, K. M.; Dicke, R.; Vorspohl,
K.; Kobs, U.; Nussbeutel, U. Tetrahedron 1989, 45, 951.
(3) Kosugi, M.; Shimizu, Y.; Migita, T. J. Organomet. Chem. 1977, 129,
C36.
(4) Milstein, D.; Stille, J. K. J. Org. Chem. 1979, 44, 1613.
(5) Verlhac, J.-B.; Chanson, E.; Jousseaume, B.; Quintard, J.-P. Tetrahedron
Lett. 1985, 26, 5997. See also: Kosugi, M.; Naka, H.; Harada, S.; Sano, H.;
Migita, T. Chem. Lett. 1987, 16, 1371.
(11) (a) Krongauz, E. S. Russ. Chem. ReV. 1977, 46, 59. (b) Shi, Q.-A.; Wang,
J.-G.; Cai, K. Youji Huaxue 1999, 19, 559. (c) Mosnacek, J.; Lukac, I. Chem.
Listy 2005, 99, 421. (d) Landais, Y.; Vincent, J. M. Sci. Synth. 2005, 26, 647.
(12) (a) Leyendecker, J.; Niewihner, U.; Steglich, W. Tetrahedron Lett. 1983,
24, 2375. (b) Ahmad, S.; Iqbal, J. J. Chem. Soc., Chem. Commun. 1987, 692.
(c) Katritzky, A. R.; Lang, H. J. Org. Chem. 1995, 60, 7612. (d) Katritzky,
A. R.; Wang, Z.; Lang, H.; Feng, D. J. Org. Chem. 1997, 62, 4125. (e) Lee,
J. C.; Park, H.-J.; Park, J. Y. Tetrahedron Lett. 2002, 43, 5661. (f) Habel, L. W.;
De Keersmaecker, S.; Wahlen, J.; Jacobsa, P. A.; De Vos, D. E. Tetrahedron
Lett. 2004, 45, 4057.
(6) Tanaka, M. Tetrahedron Lett. 1980, 21, 2959.
(7) Hua, R.; Takeda, H.; Abe, Y.; Tanaka, M. J. Org. Chem. 2004, 69, 974.
3958 J. Org. Chem. 2009, 74, 3958–3961
10.1021/jo802814r CCC: $40.75 2009 American Chemical Society
Published on Web 04/09/2009

TABLE 1. Reaction of r-Oxo Acid Chloride 1 with
but-3-en-1-one (11%) and 1-phenylbut-2-en-1-one (7%; the E/Z
ratio was ca. 2/1) were formed.13 Likewise, another RhCl(PPh3)3-
catalyzed reaction (80 °C for 5 h) of 1a with (phenylethynyl)tri-
n-butylstannane 2D, which is one of the most reactive stannane
reagents in transmetalation chemistry,14 also failed to give the
desired 1,4-diphenylbut-3-yne-1,2-dione, ending up with the
formation of diphenylacetylene (5%) and 1,4-diphenylbutadiyne
(34%). In contrast to these, a control experiment with 1a and
2A run in the absence of the catalyst at 80 °C for 3 h afforded
the desired diketone 3aA in 54% yield. These experiments
indicate that the rhodium complex promotes the reaction rapidly,
but in an undesired direction.
Organostannane 2a
entry
1, R2 )
1a, Ph
1a
1a
1a
1a
2, R2 )
2A, allyl
2B, Ph
2C, vinyl
2D, phenylethynyl
2E, benzyl
product, yield (%)b
1
2
3
4
5
3aA, (96)
3aB, 99c (95)
3aC, quant
3aD, quant (93)
3aE, 88
6
7
8
9
10
11
1a
2F, n-Bu
2B
2B
2B
2B
3aF, 98
1b, p-MeOC6H4
1c, p-ClC6H4
1d, C6F5
1e, 2-thienyl
1f, Me
3bB, quant
3cB, 97
3dB, 98d
3eB, quant
2B
3fB, 97c
a Reaction conditions: a mixture of 1 (0.5 mmol), 2 (0.5 mmol), and
b
1
toluene (3 mL) was stirred for 3 h at 110 °C. Determined by H NMR
spectroscopy with 1,1,2,2-tetrachloroethane as an internal standard. The
numbers in parentheses are isolated yields. c Determined by GC with
n-tetradecane as an internal standard. d Determined by 19F NMR
spectroscopy with hexafluorobenzene as an internal standard.
tioned, phenyl-, vinyl-, ethynyl-, and benzylstannanes 2B-E
all reacted smoothly with 1a, affording near-quantitative yields
of corresponding 1,2-diketones. More amazing is that even tetra-
n-butylstannane 2F, which is envisioned to be least reactive in
electrophilic substitution,1b,14 does react without any difficulty,
ending up with a near-quantitative yield. Since the reactivity
of phenyltri-n-butylstannane 2B is so high, the substituent-
dependent difference in reactivity is not evident as far as
substituted phenyl-2-oxoacetyl chlorides 1b-d are concerned.
The reaction of heteroaromatic (1e) and aliphatic (1f) R-oxo
acid chlorides also proceeds as well, thus proving that the
reaction offers a straightforward and general methodology for
the synthesis of various 1,2-diketones. Note that, although the
reaction listed in Table 1 was run for 3 h, a long duration of
the reaction may not be required, depending on the combination
of 1 and 2, as the time-course experiment with 1b and 2B (vide
supra) suggests.
We have also attempted the reaction of 1a with (trimethyl-
silyl)tri-n-butylstannane (100 °C, 3 h), aiming at the synthesis
of either 1-phenyl-2-(trimethylsilyl)ethane-1,2-dione or
1-phenyl-2-(tri-n-butylstannyl)ethane-1,2-dione.15,16 However,
none of these were formed at all and both starting materials
remained unchanged. Likewise the reaction with hexa-n-
butyldistannane did not form stannyl diketone either, although
a trace of chlorotri-n-butylstannane was detected in the resulting
mixture.
FIGURE 1. Time-course of the reaction of 1b with 2B in the absence
(O) or presence (b) of chlorotri-n-butylstannane monitored by 1H NMR
spectroscopy.
Another aspect that merits consideration is the possible role
of the coproduced chlorotri-n-butylstannane as a Lewis acid
catalyst. The time-course of the reaction of p-anisyl-2-oxoacetyl
chloride 1b and phenyltri-n-butylstannane 2B (1 equiv) run at
80 °C in toluene-d8 did not display a clear sigmoidal increase
of the yield of 1-(p-anisyl)-2-phenylethanedione 3bB, which
should have been seen in an autocatalytic reaction (Figure 1).
However, the same reaction run in the presence of a catalytic
quantity of chlorotri-n-butylstannane (10 mol %) was distinctly
faster, in particular in the early stages, suggesting that chlorotri-
n-butylstannane does work as a catalyst, albeit weakly.
SCHEME 2. Aluminum Chloride-Catalyzed Reaction of
Phenyl-2-oxoacetyl Chloride with Phenyltri-n-butylstannane
To gain a rough estimate of the catalytic activity of chlorotri-
n-butylstannane relative to trichloroaluminum, we ran a reaction
of phenyl-2-oxoacetyl chloride 1a with phenyltri-n-butylstan-
nane 2B (1 equiv) in the presence of trichloroaluminum (10
mol %) in dichloromethane (2 mL) at -30 °C for 3 h (Scheme
2). Analysis of the mixture by GC revealed the formation of
benzil 3aB in 53% along with benzophenone (22%). The result
indicates that trichloroaluminum promotes the reaction as a
powerful Lewis acid even at a low temperature, but the
benzophenone formation via decarbonylation is a serious
drawback.
(13) Other unidentified byproducts were also formed. Although Kosugi and
co-workers reported higher yields for the RhCl(PPh3)3-catalyzed reaction (40 °C)
of simple acid chlorides with 2A, use of a large excess of acid chlorides appears
prerequisite for the high yield, which may be associated with the decarbonylation
of acid chlorides. See ref 3.
(14) Davies, A. G. Organostannane Chemistry; VCH: Weinheim, Germany,
1997; p 58.
(15) Simple acid chlorides are known to form silyl ketones when treated
with a disilane in the presence of palladium catalysts. See: (a) Eaborn, C.;
Griffiths, R. W.; Pidcock, A. J. Organomet. Chem. 1982, 225, 331. (b) Ricci,
A.; Degl’Innocenti, A.; Chimichi, S.; Fiorenza, M.; Rossini, C. J. Org. Chem.
1985, 50, 130. (c) Yamamoto, K.; Hayashi, A.; Suzuki, S.; Tsuji, J. Organo-
metallics 1987, 6, 974. Similar reaction with a distannane affords stannyl ketones.
See: (d) Mitchell, T. N.; Kwetkat, K. J. Organomet. Chem. 1992, 439, 127.
(16) In transmetalation between (trimethylsilyl)tri-n-butylstannane (Si-Sn) and
an organopalladiumhalide complex (R-Pd-X), formation of both R-Pd-Si and
R-Pd-Sn appears possible, depending on the particular structure of the complex.
See: (a) Mori, M.; Kaneta, N.; Shibasaki, M. J. Org. Chem. 1991, 56, 3486. (b)
Obora, Y.; Tsuji, Y.; Kawamura, T. J. Am. Chem. Soc. 1995, 117, 9814.
The new methodology described in the representative experi-
ment appears quite general, irrespective of the structure of R-oxo
acid chlorides and organostannane compounds as summarized
in Table 1. Thus, besides the allylstannane 2A already men-
J. Org. Chem. Vol. 74, No. 10, 2009 3959

medicinally active compounds.19 They are also versatile inter-
mediates in synthetic applications, for instance, the synthesis
of heterocyclic compounds20 and ligands for inorganic com-
plexes.21 Accordingly, synthesis of 1,2-diketones has been a
subject of extensive research and numerous methodologies have
been proposed,11 mainly by oxidation of ketones or R-func-
tionalized ketones,12,22e 1,2-diols,12f,23 alkynes,20g,24 olefins,25
epoxides,26 and 1,2-dihalides27 and also by other miscellaneous
methods.28 We envision that the new findings herein reported
will find broad utility in organic synthesis.
SCHEME 3. 1,2-Diketone Synthesis Starting with Oxalyl
Chloride
Experimental Section
Typical Procedure for the Reaction of r-Oxo Acid Chlorides
with Organostannanes: The Reaction of Phenyl-2-oxoacetyl Chlo-
ride (1a) with Allyltri-n-butylstannane (2A). A mixture of phenyl-
2-oxoacetyl chloride 1a (85 mg, 0.51 mmol) and allyl(tri-n-
butyl)stannane (2A, 0.15 mL, 0.48 mmol) in toluene (4 mL) was
heated for 3 h at 110 °C. After cooling to room temperature, the
mixture was analyzed by 1H NMR spectroscopy by using 1,1,2,2-
tetrachloroethane (9.2 mg) added as an internal standard. Then the
reaction mixture was diluted with methyl tert-butyl ether (10 mL)
and a 5 mL portion of a saturated aqueous KF solution (ca. 10 wt
%) was added. The organic layer was separated from the resulting
suspension. Another 5 mL portion of the KF solution was added
and the mixture was processed similarly. The organic layer
separated from the second KF treatment was dried over Na2SO4,
filtered, and evaporated. The residue was subjected to preparative
TLC (silica gel, hexane/acetone ) 85/15) to give 1-phenylpent-4-
Encouraged by the high-yielding synthesis of 1,2-diketones,
we assumed that oxalyl chloride 4 could form 1,2-diketone when
treated with organostannanes, which indeed turned out to be a
convenient modification in two directions. One is the synthesis
of symmetrical diketone, as exemplified by the synthesis of
benzil as shown in Scheme 3 (top). Heating a toluene solution
of 4 and 2 equiv of phenyltri-n-butylstannane 2B at 110 °C for
5 h gave benzil 3aB in 89% GC yield. In the other (Scheme 3,
bottom), to a toluene solution of 4 was added a toluene solution
of phenyltri-n-butylstannane 2B (1 equiv) at 60 °C, slowly by
using a syringe pump. After heating for another 2 h, (phenyl-
ethynyl)tri-n-butylstannane 2D (1 equiv) in toluene was added
in one portion to the resulting mixture and the mixture was
further heated for 3 h. GC analysis revealed the formation of
1,4-diphenylbut-3-yne-1,2-dione 3aD (78% GC yield) along
with benzil 3aB (14% GC yield). Similar reactions with allyltri-
n-butylstannane 2A, vinyltri-n-butylstannane 2C, and tetra-n-
butylstannane 2F in place of 2D also furnished corresponding
1,2-diketones (3aA, 3aC, and 3aF) in 71-76% yields, together
with benzil 3aB. These reactions suggest that R-oxo acid
chlorides 1, synthesis of which occasionally requires tedious
multistep processes, including the preparation of R-oxo acids17
and subsequent chlorination,18 using toxic reagents, can be
generated rather cleanly. To substantiate the suggestion, a
toluene solution of phenyltri-n-butylstannane 2B was added at
70 °C slowly over a period of 2 h by using a syringe pump to
a toluene (5 mL) solution of oxalyl chloride 4 (1 equiv) and
the mixture was heated for another 2 h. Analysis by GC revealed
the formation of phenyl-2-oxoacetyl chloride 1a in 76% yield.
This in situ generation of R-oxo acid chloride is also of great
synthetic value in its own right.
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To summarize we have developed a transition metal-catalyst-
free coupling of R-oxo acyl chlorides with organostannanes,
which serves as a general, simple, and high-yielding methodol-
ogy to synthesize 1,2-diketones. An easy synthesis of R-oxo
acyl chlorides has also been made possible via coupling of oxalyl
chlorides with organostannanes. 1,2-Diketones are useful as
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3960 J. Org. Chem. Vol. 74, No. 10, 2009

ene-1,2-dione 3aA (81 mg, 0.46 mmol, 96% isolated yield) as pale
yellow oil. 1H NMR δ 7.99 (dd, J ) 1.07, 8.3 Hz, 2H, o-Ph), 7.65
(t, J ) 7.1 Hz, 1H, p-Ph), 7.54-7.39 (m, 3H, m-Ph and HHCdCH,
oxalyl chloride (62.8 mg, 0.498 mmol) and toluene (5 mL) placed
in a 20 mL Schlenk tube was added a solution of phenyltri-n-
butylstannane (185 mg, 0.504 mmol) in toluene (2 mL) slowly over
a period of 2 h by using a syringe pump and the mixture was heated
for another 2 h at that temperature. Subsequently, (phenylethynyl)tri-
n-butylstannane (199 mg, 0.509 mmol) was added in one portion
and the mixture was heated for an additional 3 h. GC analysis with
tetradecane (11.3 mg) as internal standard revealed the formation
of 3aD in 78% yield along with benzil in 14% yield.
3
3
3
overlapped), 7.01 (ddt, JHH-trans ) 16.0 Hz, JHH ) 6.8, JHH-cis
)
10.1 Hz, 1H, HHCdCH), 6.48 (dd, 3JHH ) 1.5 Hz, 3JHH-trans ) 16.0
Hz, 1H, HHCdCH), 2.02 (d, 3JHH ) 6.8 Hz, 2H, COCH2); 13C{1H}
NMR δ 194.2 (CO), 194.0 (CO), 151.5 (COCCC), 135.0 (COCCC),
133.1 (ipso-Ph), 130.4 (o-Ph), 129.2 (m-Ph), 129.0 (p-Ph), 19.6
(COCCC); IR (neat, cm-1) 1674 (br, νCO), 1624 (νCdC); GCMS
(70 eV) m/z (% rel intensity) 174 (12, [M]+), 105 (100), 77 (12),
69 (21); HRMS (EI) calcd for C11H10O2 174.0681, found 174.0684.
For 1H and 13C NMR spectra, see appendices 3 and 4 in the
Supporting Information.
Reaction of Oxalyl Chloride with Phenyltri-n-butyl-
stannane. To oxalyl chloride (63.0 mg, 0.496 mmol) and toluene
(3 mL) placed in a 20 mL Schlenk tube was added phenyltri-n-
butylstannane (368 mg, 1.00 mmol) and the mixture was heated at
110 °C for 5 h. GC analysis with tetradecane (6.3 mg) as internal
standard revealed the formation of benzil in 89% yield.
Acknowledgment. This work was supported by a Grant-in-
Aid for Scientific Research on Priority Areas (No. 18065008)
from the Ministry of Education, Culture, Sports, Science and
Technology, Japan and by a research fellowship to T.K. from
the Japan Society for the Promotion of Science and Technology.
Supporting Information Available: Experimental details and
spectral data of new compounds. This material is available free
of charge via the Internet at http://pubs.acs.org.
Synthesis of 1,2-Diphenylbut-3-yne-1,2-dione (3aD) by the
Reaction of Oxalyl Chloride with Phenyltri-n-butylstannane
Followed by (Phenylethynyl)tri-n-butylstannane. At 60 °C, to
JO802814R
J. Org. Chem. Vol. 74, No. 10, 2009 3961