Palladium-Catalyzed Hydrocarboxylation of Allenes

Full text of DOI:10.1021/ja974223+

J. Am. Chem. Soc. 1998, 120, 3809-3810
3809
Table 1. Palladium-Catalyzed Hydrocarboxylation of Allenesa
Palladium-Catalyzed Hydrocarboxylation of Allenes
Mohammad Al-Masum† and Yoshinori Yamamoto*
Institute for Chemical Reaction Science and
Department of Chemistry
Graduate School of Science
Tohoku UniVersity, Sendai 980-77, Japan
ReceiVed December 15, 1997
The ability of transition metal complexes to activate organic
molecules makes them attractive prospects for developing catalytic
processes with high selectivity and high atom economy.1 In our
continuing study on hydrocarbonation,2 hydroamination,3and
hydrosulfination4 of allenes to develop a new process for eco-
chemistry, we concentrated on the addition of carboxylic acids
(hydrocarboxylation) to allenes. The addition of HX (X )
halogen) to olefins through carbenium ions is a classical elec-
trophilic reaction. The addition of HCl to phenylallene, which
proceeds through an R-vinylbenzyl cation, has also been reported.5
However, to the best of our knowledge, transition metal catalyzed
carboxylic acid addition to allenes is not known. On the other
hand, the transition metal catalyzed inter- and intramolecular
addition of carboxylic acids to alkynes is well-known,6and the
intramolecular cyclization of alkenoic acids catalyzed by pal-
ladium complexes is also known.7We wish to report that various
types of carboxylic acids 2 smoothly react with allenes 1 in the
presence of a catalytic amount (0.5-1.0 mol %) of Pd2(dba)3‚
CHCl3/dppf complex, affording the corresponding allyl esters 3
in high chemical yields (eq 1). In contrast to the classical
† Institute for Chemical Reaction Science, Tohoku University, Sendai 980-
77, Japan.
(1) (a) Trost, B. M. Science 1991, 254, 1471. (b) Murai, S.; Kakiuchi, F.;
Sekine, S.; Tanaka, Y.; Kamatani, A.; Sonoda, M.; Chatani, N. Nature 1993,
366, 529. (c) Tsuji, J. In Palladium Reagents and Catalyst; John Wiley &
Sons: Chichester, 1995; pp 21-124.
(2) (a) Yamamoto, Y.; Al-Masum, M.; Asao, N. J. Am. Chem. Soc. 1994,
116, 6019. (b) Yamaguchi, M.; Omata, K.; Hirama, M. Tetrahedron Lett. 1994,
35, 5689. (c) Trost, B. M.; Gerusz, V. J. J. Am. Chem. Soc. 1995, 117, 7,
5156. (d) Yamamoto, Y.; Al-Masum, M.; Fujiwara, N.; Asao, N. Tetraheron
Lett. 1995, 36, 2811. (e) Yamamoto, Y.; Al-Masum, M. Synlett 1995, 969.
(f) Besson, L.; Gore, J.; Cazes, B. Tetrahedron Lett. 1995, 36, 3853. (g)
Yamamoto, Y.; Al-Masum, M.; Fujiwara, N. J. Chem. Soc., Chem. Commun.
1996, 381. (h) Yamamoto, Y.; Al-Masum, M.; Takeda, A. J. Chem. Soc.,
Chem. Commun. 1996, 831.
(3) (a) Besson, L.; Gore, J.; Cazes, B. Tetrahedron Lett. 1995, 36, 3857.
(b) Al-Masum, M.; Meguro, M.; Yamamoto, Y. Tetrahedron Lett. 1997, 38,
6071 and references therein.
(4) Kamijo, S.; Al-Masum, M.; Yamamoto, Y. Tetrahedron Lett. 1998,
39, 691.
(5) (a) Okuyama, T.; Izawa, K.; Fueno, T. J. Am. Chem. Soc. 1973, 95, 5,
6749. (b) Izawa, K.; Okuyama, T.; Sakagami, T.; Fueno, T. J. Am. Chem.
Soc. 1973, 95, 6752. (c) Summerville, R. H.; Schleyer, P. v. R. J. Am. Chem.
Soc. 1974, 96, 1110. The addition of trifluoroacetic acid to allenes was
investigated. The major product was their isomerized acetylenes, and the
adducts (vinyltrifluoroacetates) were obtained as a minor product.
(6) (a) Mitsudo, T.; Hori, Y.; Yamakawa, Y.; Watanabe, Y. J. Org. Chem.
1987, 52, 2230. (b) Chan, D. M. T.; Marder, T. B.; Milstein, D.; Taylor, N.
J. J. Am. Chem. Soc. 1987, 109, 6385. (c) Trost, B. M.; Brieden, W. Angew.
Chem., Int. Ed. Engl. 1992, 31, 1335. (d) Doucet, H.; Martin-Vaca, B.;
Bruneau, C.; Dixneuf, H. J. Org. Chem. 1995, 60, 7247 and references therein.
(7) Cyclization of alkenoic acids: Larock, R. C.; Hightower, T. R. J. Org.
Chem. 1993, 58, 5298 and references therein. Two equivalents of NaOAc
were used for the palladium-catalyzed addition of carboxylic acid to olefins
and thus perhaps carboxylate RCO2- is formed in situ, although Prof. Larock
does not mention this mechanism. Palladium would coordinate to olefin, and
then the carboxylate would attack the electron-deficient olefin. Accordingly,
the reaction most probably proceeds through the usual type of addition of
nucleophiles to Pd(II)-coordinated alkene.
a All yields are of pure products isolated by column chromatography.
1H NMR and elemental analysis either by combustion or high resolution
mass spectrometry (HRMS) are satisfactory. b The ratio of E/Z was
1
50/50, determined by H NMR. c E/Z ) 75/25. d E/Z ) 80/20.
electrophilic addition reaction, the new version of hydrocarbox-
ylation reaction of allenes most probably proceeds through
π-allylpalladium species.
The results are shown in Table 1. In initial experiments
phenylallene 1a was treated with 1 mol % Pd2dba3‚CHCl3 and 2
mol % dppf in THF with 1.1 equiv of acetic acid 2a. When this
reaction was carried out at room temperature, no addition product
was detected. Then the reaction mixture was heated at 80 °C for
4 h. The hydrocarboxylation product, cinnamyl acetate 3a, was
isolated in 83% yield exclusively as the E isomer (proven by NMR
spectroscopy) (entry 1). No addition product was obtained in
the absence of palladium catalyst. As the catalyst, Pd(Ph3P)4/
dppf was moderately effective and [(η-C3H5)PdCl]2/dppf was less
effective. Other catalysts such as Pd(OAc)2, PdCl2(dppe),
Pt(Ph3P)4, PtCl2(Ph3P)2, K2PtCl4, RhH(CO)(Ph3P)2, and RuH2-
S0002-7863(97)04223-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/02/1998

3810 J. Am. Chem. Soc., Vol. 120, No. 15, 1998
Communications to the Editor
(Ph3P)4 were ineffective. When Pd2(dba)3‚CHCl3/dppf was used
as the catalyst, the reactions of various allenes with various
carboxylic acids were examined. When aryllallenes with an
electron-donating group at the para position (e.g., p-MeO-C6H4-,
1b) and an electron withdrawing group at the para position (e.g.,
p-F3C-C6H4-, 1c) were treated with acetic acid, the hydrocar-
boxylation proceeded smoothly and gave the corresponding allyl
acetates 3b and 3c, respectively, in a regio- and stereoselective
manner (entries 2 and 3). The addition of propionic acid 2b to
1b proceeded satisfactorily (entry 4). With benzoic acid 2c, the
addition to allene 1a, 1b, and p-bromophenylallene 1d gave the
corresponding allyl esters 3e, 3f, and 3g, respectively, in very
high yields (entries 5-7). The hydrocarboxylation of 1a, 1b,
and p-chlorophenylallene 1e with cinnamic acid 2d proceeded
very smoothly, giving the corresponding carboxylates 3h, 3i, and
3j, respectively, in good yields (entries 8-10). When p-
methoxyphenylallene was treated with Boc-L-alanine 2e, the
corresponding allyl ester of Boc-L-alanine 3k was obtained in
good yield without affecting the functional groups (entry 11). R,R-
Disubstituted allenes, 1f and 1g, reacted very smoothly with 2a
to give the corresponding allylic carboxylates 3l and 3m,
respectively, in good to high yields (entries 12-13). Very
interestingly, phenylthioallene 1h underwent the hydrocarbox-
ylation reaction without any problem to afford the acetoxylate
3n having a vinylthio group in high yield (entry 14).
Scheme 1
A typical procedure is as follows. To a dry reaction vial (the
Wheaton microreactors), charged with Pd2dba3‚CHCl3 (0.005
mmol, 5.5 mg), dppf (0.01 mmol, 6.0 mg), and THF (0.5 mL),
were added acetic acid (0.55 mmol, 0.04 mL) and phenylallene
1a (0.5 mmol, 0.068 mL), and the reaction mixture was heated
at 80 °C for 4 h. The mixture was filtered through a short alumina
column. Removal of the solvent in vacuo followed by silica gel
column chromatography with hexane/ethyl acetate (60/1) as an
eluent provided pure cinnamyl acetate in 83% yield (73.0 mg).
Various allenes were prepared by the reaction of aryl (or alkyl)
copper reagents with propargyl tosylates.9 Phenylthioallene was
prepared from phenylthiocopper complex with propargyl chlo-
ride.10
In the case of aliphatic allenes, 1,3-butadiene type products
were formed;8 the reaction of a 1,1-disubstituted allene 4 with
acetic acid gave an isomerized 1,3-butadiene 5 (E: Z ) 1:1) in
50% yield (eq 2). Furthermore, R-aryl- and γ-methyl-substituted
A plausible mechanism for the new catalytic reaction is shown
in Scheme 1. Insertion of Pd(0) would produce hydridopalladium
species 7. Hydropalladation of an allene with 7 would give a
π-allylpalladium intermediate 8, which would afford allylcar-
boxylate 3 and Pd(0) via reductive elimination.
A remarkable feature of the present reaction is its efficiency,
especially the high yields of hydrocarboxylated products under
mild conditions with excellent regio- and stereoselectivity (in the
case of the monosubstituted allenes). A new version of H-O2CR
addition to allenes most probably involves hydridopalladium
species followed by π-allyl complex, instead of a carbenium ion
intermediate in classical electrophilic addition. The molar ratio
of reactant/catalyst is high enough for a synthetic reaction and
the catalytic process described here may be useful for synthesizing
a new range of allylated esters.
allenes 6a,b,c, gave 1-aryl-1,3-butadienes in ca. 50% yields upon
treatment with acetic acid-Pd catalyst (eq 3). Accordingly, if
Supporting Information Available: Full spectroscopic and analytical
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there is an allylic hydrogen in aliphatic allenes, â-hydride
elimination from the π-allylpalladium intermediate 8 (Vide post)
predominates over reductive coupling, giving the diene derivatives
as a major product.
JA974223+
(9) Vermer, P.; Meijer, J.; Brandsma, L. Recl. TraV. Chim. Pays-Bas 1975,
94, 112.
(10) Bridges, A. J. Tetrahedron Lett. 1980, 21, 4401.
(8) (a) Tsuji, J. In AdV. Org. Chem. 1979, 17, 141-193. (b) Shimizu, I.;
Sugiura, I.; Tsuji, J. J. Org. Chem. 1985, 50, 537.