C O M M U N I C A T I O N S
Table 1. Generality of 1,1-Disubstituted Allenes
and a CIF file for 1. This material is available free of charge via the
References
(1) Reviews on transition metal-promoted CO2-fixation reactions; see: (a)
Sakakura, T.; Choi, J.-C.; Yasuda, H. Chem. ReV. 2007, 107, 2365. (b)
Yin, X.; Moss, J. R. Coord. Chem. ReV. 1999, 181, 27. (c) Braunstein, P.;
Matt, D.; Nobel, D. Chem. ReV. 1988, 88, 747.
(2) (a) Johansson, R.; Wendt, O. F. Dalton Trans. 2007, 488. (b) Shi, M.;
Nicholas, K. M. J. Am. Chem. Soc. 1997, 119, 5057.
(3) (a) Ukai, K.; Aoki, M.; Takaya, J.; Iwasawa, N. J. Am. Chem. Soc. 2006,
128, 8706. (b) Takaya, J.; Tadami, S.; Ukai, K.; Iwasawa, N. Org. Lett.
2008, 10, 2697. (c) Ohishi, T.; Nishiura, M.; Hou, Z. Angew. Chem., Int.
Ed. 2008, 47, 5792.
(4) (a) Yeung, C. S.; Dong, V. M. J. Am. Chem. Soc. 2008, 130, 7826. (b)
Ochiai, H.; Jang, M.; Hirano, K.; Yorimitsu, H.; Oshima, K. Org. Lett.
2008, 10, 2681.
(5) Mori et al. developed nucleophilic carboxylation of allylnickel intermediates
generated by Ni(0)-promoted oxidative cyclization of bis(1,3-diene)s or
TMS-substituted allenes with CO2. See: (a) Takimoto, M.; Kawamura, M.;
Mori, M.; Sato, Y. Synlett 2005, 2019. (b) Takimoto, M.; Nakamura, Y.;
Kimura, K.; Mori, M. J. Am. Chem. Soc. 2004, 126, 5956. (c) Takimoto,
M.; Mori, M. J. Am. Chem. Soc. 2002, 124, 10008.
(6) Cu-Catalyzed nucleophilic alkynylation of CO2 using terminal alkyne as
substrates was reported; see: (a) Oi, S.; Fukue, Y.; Nemoto, K.; Inoue, Y.
Macromolecules 1996, 29, 2694. (b) Fukue, Y.; Oi, S.; Inoue, Y. J. Chem.
Soc., Chem. Commun. 1994, 2091.
a 2.5 mol% of 1 was employed. b dr ) 91:9. c Isolated as its methyl
ester after treatment with TMSCHN2.
(7) Transition metal catalyzed reactions of allenes with CO2 were reported
although their catalytic activity, scope, yield, and product selectivity were
not satisfactory; see: (a) Tsuda, T.; Yamamoto, T.; Saegusa, T. J.
Organomet. Chem. 1992, 429, C46. (b) De´rien, S.; Clinet, J.-C.; Dun˜ach,
E.; Pe´richon, J. Synlett 1990, 361. (c) Sasaki, Y. J. Mol. Catal. 1989, 54,
L9. (d) Aresta, M.; Quaranta, E.; Ciccarese, A. C1 Mol. Chem. 1985, 1,
283. (e) Do¨hring, A.; Jolly, P. W. Tetrahedron Lett. 1980, 21, 3021.
(8) Reductive allylation of other carbonyl compounds using allene substrates
were recently reported; see: (a) Skucas, E.; Bower, J. F.; Krische, M. J.
J. Am. Chem. Soc. 2007, 129, 12678. (b) Bower, J. F.; Skucas, E.; Patman,
R. L.; Krische, M. J. J. Am. Chem. Soc. 2007, 129, 15134. (c) Ngai, M.-
Y.; Skucas, E.; Krische, M. J. Org. Lett. 2008, 10, 2705.
Table 2. Carboxylation of Mono- or Disubstituted Allenes
(9) Synthesis of several tridentate PSiP-pincer complexes have been reported
although they have rarely been used as a catalyst in synthetic organic
chemistry; see: (a) Gossage, R. A.; McLennan, G. D.; Stobart, S. R. Inorg.
Chem. 1996, 35, 1729. (b) Brost, R. D.; Bruce, G. C.; Joslin, F. L.; Stobart,
S. R. Organometallics 1997, 16, 5669. (c) MacInnis, M. C.; MacLean,
D. F.; Lundgren, R. J.; McDonald, R.; Turculet, L. Organometallics 2007,
26, 6522. and references cited therein. See also: (d) Balakrishna, M. S.;
Chandrasekaran, P.; George, P. P. Coord. Chem. ReV. 2003, 241, 87. (e)
Minato, M.; Zhou, D.-Y.; Sumiura, K.-i.; Hirabayashi, R.; Yamaguchi, Y.;
Ito, T. Chem. Commun. 2001, 2654. (f) Minato, M.; Matsumoto, T.;
Ichikawa, M.; Ito, T. Chem. Commun. 2003, 2968. (g) Korshin, E. E.;
Leitus, G.; Shimon, L. J. W.; Konstantinovski, L.; Milstein, D. Inorg. Chem.
2008, 47, 7177.
(10) Allyl palladium complexes bearing PCP-pincer ligand are reported to act
as nucleophilic allylation catalyst; see: Szabo´, K. J. Synlett 2006, 811.
(11) See ref 9 and references cited therein.
(12) Oligomerization of allene was often observed as a side reaction; see ref
7e.
(13) 1 was synthesized in good yield by ligand exchange of ClPd(PSiP) 2 with
AgOTf. The structure of 1 was confirmed by X-ray analysis. For detailed
procedure and ORTEP diagram, see Supporting Information.
(14) Turculet and co-workers reported preparation of 2 during this research was
in progress; see ref 9c.
a 1.0 mol% of
1
was employed. b Yields were determined as
carboxylic acid without esterification. c E/Z ) 69:31.
that a small amount of γ-substituted ꢀ,γ-unsaturated carboxylic
acids 7 and R,ꢀ-unsaturated acids 8 were obtained, which were
regioisomers in the carboxylation and hydrometalation step,
respectively.
In conclusion, we have developed a novel catalytic hydrocar-
boxylation of allenes by utilizing a silyl pincer-type palladium
complex as the catalyst. This protocol is highly attractive not only
as a CO2-fixation reaction but also as a methodology for the
synthesis of ꢀ,γ-unsaturated carboxylic acids due to its wide
generality and high efficiency. Detailed mechanistic studies and
application of this catalysis to other substrates are ongoing in our
group.
(15) Other solvents such as toluene, 1,4-dioxane, and THF resulted in lower
conversion under the same conditions.
(16) 2 did not show catalytic activity under the same conditions probably due
to its lower activity for initial transmetalation with AlEt3.
(17) Other reducing agents such as Et3SiH and BEt3 did not afford the product.
(18) The possibility that the carboxylation occurs not with D but with an
allylaluminum intermediate generated by metal exchange should be
considered. However, the reaction in Scheme 2 just without CO2 afforded
only 9% of 3-methyl-5-phenyl-1-pentene, and 78% of 3a was recovered.
Even when the same reaction was run in the presence of diethylaluminum
carboxylate, nearly the same result was obtained. These results strongly
suggest that the exchange of allylpalladium to allylaluminum did not occur
to an appreciable amount under the present reaction conditions and
carboxylation occurs mainly with the allylpalladium intermediate.
(19) The stereochemistry was not determined.
Acknowledgment. This research was partly supported by a
Grant-in-Aid for Scientific Research from the Ministry of Education,
Culture, Sports, Science, and Technology of Japan. We thank Ms.
Sachiyo Kubo for performing X-ray analysis.
(20) The use of AlEt3 caused isomerization of the product to R,ꢀ-unsaturated
carboxylic acid.
Supporting Information Available: Preparative methods and
spectral and analytical data of compounds 1-8 and ORTEP diagram
JA806677W
9
J. AM. CHEM. SOC. VOL. 130, NO. 46, 2008 15255