Double acylation of alkenes with acylchromates promoted by cationic Pd(II) complex

Article abstract of DOI:10.1246/cl.2000.174

Double acylation of alkenes such as norbornene and vinyl-silane proceeds by the use of acylchromate complexes and a cationic Pd(II) complex. When two different acylchromates are added successively to a mixture of alkene and the Pd complex, unsymmetrical diketones are obtained almost selectively.

Full text of DOI:10.1246/cl.2000.174

174
Chemistry Letters 2000
Double Acylation of Alkenes with Acylchromates Promoted by Cationic Pd(II) Complex
Motoki Yamane, Yuichiro Ishibashi, Hidehiro Sakurai, and Koichi Narasaka*
Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033
(Received November 15, 1999; CL-990975)
Double acylation of alkenes such as norbornene and vinyl-
silane proceeds by the use of acylchromate complexes and a
cationic Pd(II) complex. When two different acylchromates
are added successively to a mixture of alkene and the Pd com-
plex, unsymmetrical diketones are obtained almost selectively.
Palladium catalyzed carbonylation reactions have found a
wide application in organic synthesis, where acylpalladium
complexes play an important role as key intermediates.1
Generally, acylpalladium species are generated by two meth-
ods; (i) oxidative addition of acyl halides to Pd(0) complexes
(ii) insertion of carbon monoxide to alkylpalladium complexes.
As compared with these methods, metal exchange between
acylmetals and Pd(II) compounds has not found a wide utility
due to the limitation of acylmetals suitable for transmetalla-
tion. Though acyl stannanes,2 iron,3 nickel,3 and zirconium4
compounds have been employed as acyl sources, these acyl-
metals have some drawbacks such as difficulty of their synthe-
sis, instability in the air, toxicity, or necessity of high tempera-
ture in the transmetallation step.
Tetraalkylammonium acylchromates are relatively stable
and easy to be synthesized. Recently, we reported that Pd(0)-
catalyzed acylation reactions of allylic halides by using acyl-
chromates 1 as donors of acyl groups (eq. 1).5
Pd(CH3CN)4(BF4)2 (2).7 In fact, the double acylation product
3a was obtained in 84% yield without the formation of 4a (entry
3). Thus palladium complexes particularly the cationic complex
promoted the double acylation, whereas 3a was not obtained in
the reaction with Pt and Ni compounds (entries 4 and 5).
Double acylation of norbornene with aroyl chromates
1a–c and the cationic palladium complex 2 proceeds smoothly
to afford the cis–exo diketones 3a–c stereoselectively in good
yield (entries 3, 6 and 7).8,9 Alkanoylchromate 1d is also uti-
lizable for this reaction (entry 8). When norbornadiene is
employed instead of norbornene, two cis diacylated products
5b, cis-exo and cis-endo diacylnorbornenes are obtained in a
2:1 ratio (entry 9).9 In addition to norbornene derivatives,
dimethylphenylvinylsilane can be transformed to diphenyl-1,4-
butanedione 6b (entry 10).
Because the metal exchange between acylchromates and
η3–allylpalladium(II) species seems to proceed at low tempera-
ture in the above reaction, we expected that double acylation of
alkenes would proceed with acylchromates and Pd(II) as
depicted in eq. 2.6
The acyl transfer from acylchromate complex 1 to
Pd(CH3CN)4(BF4)2 (2) was confirmed by isolating an acyl-
palladium intermediate. When Pd(CH3CN)4(BF4)2 (2) was
treated with 1a and triphenylphosphine in a 1:1:2 molar ratio,
acylpalladium complex 8a was isolated in 90% yield (eq. 3).
The chemical shift of 13C-NMR (δCO: 218.5 ppm) and IR spec-
Acylation of norbornene was firstly examined with Pd(II)
and 2 molar amounts of tetramethylammonium p–methoxy-
benzoylchromate 1a. The use of Pd(OAc)2 and PdCl2(CH3CN)2
were found to give the double acylation product 3a in 35% and
62%, respectively, however, α–diketone 4a, a dimer of the chro-
mate 1a, was detected as a side product (Table 1, entries 1 and
2). As it is known that cationic acylpalladium(II) species exhibit
higher reactivity in the addition reaction to alkenes than neutral
acylpalladiums, the acylation was examined with
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
175
tra (νCO: 1666, 1643 cm-1) of 8a support the structure of acyl-
palladium complex by the comparison with those of analogous
acylpalladium complexes in the literatures.7a
As described above, a double acylation reaction of alkenes
is achieved by the use of acylchromates as acyl donors and the
cationic palladium(II) complex.
The isolation of a norbornene inserted intermediate was
also investigated by using acylchromate 1e. After the reaction
of 1e, 2 and norbornene, the resulting intermediate was
trapped with triphenylphosphine to give the known complex,
3-acetylnorborn-2-ylpalladium 9e (eq. 4).7a
References and Notes
1
a) J. Tsuji, Acc. Chem. Res., 2, 144 (1969). b) J. K. Stille,
L. F. Fries, R. W. Fries, P. K. Wong, D. E. James, and K.
S. Y. Lau, Adv. Chem. Ser., 57, 1799 (1974). c) J. Tsuji,
“Organic Synthesis with Palladium Compounds," Springer
Verlag, Heiderberg (1980). d) A. Yamamoto, T.
Yamamoto, and F. Ozawa, Pure & Appl. Chem., 57, 1799
(1985). e) D. Milstein, Acc. Chem. Res., 21, 428 (1988).
f) E. Drent, Pure Appl. Chem., 62, 661 (1990). g) A. Sen,
T. -W. Lai, J. Am. Chem. Soc., 104, 3520 (1982). h) E.
Drent, J. A. M. van Broekhoven, and M. J. Doyle, J.
Organomet. Chem., 417, 235 (1991). i) K. Nozaki, N.
Sato, Y. Tonomura, M. Yasutomi, H. Takaya, T. Hiyama,
T. Matsubara, and N. Koga, J. Am. Chem. Soc., 119,
12779 (1997). j) F. J. Parlevliet, M. A. Zuideveld, C.
Kiener, H. Kooijman, A. L. Spek, P. C. J. Kamer, and P.
W. N. M. van Leeuwen, Organometallics, 18, 3394
(1999), and references cited therein.
These results suggested the following reaction mecha-
nism. The metal exchange between 1 and 2 affords acylpalla-
dium(II) species A, which is converted to norbornyl palladi-
um(II) intermediate B. Then the acylation of the palladium
with the second acylchromate 1 forms acyl alkyl palladium
complex C, and the successive reductive elimination affords
the double acylation product 3 (Scheme 1).
2
3
J.-B. Verlhac, E. Chanson, B. Jousseaume, and J.-P.
Quintard, Tetrahedron Lett., 49, 6075 (1985).
a) L. S. Hegedus and R. Tamura, Organometallics, 1,
1188 (1982). b) T. Koga, S. Makinouchi, and N.
Okukado, Chem. Lett., 1988, 1141.
4
Y. Hanzawa, N. Tabuchi, and T. Taguchi, Tetrahedron
Lett., 39, 6249 (1998). Y. Hanzawa, N. Tabuchi, K. Saito,
S. Noguchi, and T. Taguchi, Angew. Chem., Int. Ed. Engl.,
38, 2395 (1999).
5
6
H. Sakurai, K. Tanabe, and K. Narasaka, Chem. Lett.,
1999, 309.
Recently, a Pd-catalyzed double benzoylation of norborna-
diene was reported, which was carried out by using
diphenyliodonium tetrafluoroborate and phenylboronic
acid at atmospheric pressure of carbon monoxide, see: S.-
K. Kang, J.-S. Kim, S.-C. Choi, and K.-H. Lim, Synthesis,
1998, 1249.
Mechanistic studies of the insertion of alkenes into cation-
ic acylpalladium complexes, see: a) J. S. Brumbaugh, R.
R. Whittle, M. Parvez, and A. Sen, Organometallics, 9,
1735 (1990). b) F. Ozawa, T. Hayashi, H. Koide, and A.
Yamamoto, J. Chem. Soc., Chem. Commun., 1991, 1469,
and references cited therein.
The representative procedure is as follows. To an acetoni-
trile solution of 47.3 mg (0.106 mmol) of
Pd(MeCN)4(BF)4, 39.5 mg (0.106 mmol) of tetramethy-
lammonium salt of benzoylchromate complex 1b was
added dropwise at –40 ˚C for over 30 minutes. Then 49.7
mg (0.530 mmol) of norbornene was added, followed by
the successive addition of 39.5 mg (0.106 mmol) of 1b.
The reaction mixture was allowed to room temperature,
then stirred for 12 h.
This mechanistic consideration prompted us to investigate
the unsymmetrical double acylation by the use of different
acylchromates (R1 ≠ R2 in Scheme 1). In fact, the successive
addition of two different acylchromates to a mixture of 2 and
norbornene realized the unsymmetrical three-component cou-
pling as shown in Table 2. Various unsymmetrical cis-exo dia-
cylnorbornanes are prepared in high yields. Though symmetri-
cal diketones originated from the latter acylchromates were
detected, the unsymmetrical diketones 3 were prepared almost
selectively.
7
8
9
The stereochemistry of the 2,3-bis(acyl)norbornanes and
norbornenes was determined by comparison with the
chemical shift of 1H-NMR and 13C-NMR in the literatures,
see: F. Freeman, M. Y. Lee, H. Lu, and X. Wang, J. Org.
Chem., 59, 3695 (1994). S. Arakawa, J. Org. Chem., 42,
3800 (1977) and Ref. 6.