ORGANIC
LETTERS
2009
Vol. 11, No. 24
5650-5652
Regioselective Iron-Catalyzed
Decarboxylative Allylic Etherification
Rushi Trivedi and Jon A. Tunge*
Department of Chemistry and Department of Medicinal Chemistry, The UniVersity of
Kansas, Lawrence, Kansas 66045
Received October 4, 2009
ABSTRACT
An anionic iron complex catalyzes the decarboxylative allylation of phenols to form allylic ethers in high yield. The allylation is regioselective
rather than regiospecific. This suggests that the allylation proceeds through π-allyl iron intermediates in contrast to related allylations of
carbon nucleophiles that have been proposed to proceed via σ-allyl complexes. Ultimately, iron catalysts have the potential to replace more
expensive palladium catalysts that are typically utilized for decarboxylative couplings.
Decarboxylative allylation reactions are a powerful method
for the allylation of a wide variety of nucleophiles under
Scheme 1
neutral conditions.1 A remaining issue with decarboxylative
allylations is their reliance on relatively expensive platinum
group metals. For instance, decarboxylative etherification has
been reported to occur with Pd,2 Rh,2c and more recently
Ru-based catalysts.3,4 A single example of nickel-catalyzed
decarboxylative etherification has also been reported. How-
ever, the specific reaction conditions and yield were not
included in that report.2c Herein we report that similar
transformations can be effected with simple, inexpensive
iron-based catalysts (Scheme 1).
The first palladium-catalyzed decarboxylative etherification
was reported in 1981 and Larock later generalized the
transformation into a useful method.2b Initial attempts at
enantioselective coupling were not fruitful (<23% ee);2c
however, these reactions provided the foundation for the
recent enantioselective Ru-catalyzed decarboxylative etheri-
fication.3
In looking to utilize catalysts other than standard platinum
group metals for decarboxylative etherification, we were
drawn to the seminal iron-catalyzed allylic alkylations of
Roustan5 and more recently Plietker.6 More specifically,
Plietker has used phosphine and N-heterocyclic carbene-
modified versions of the Hieber anion to form electrophilic
allyl species from allylic carbonates. However, Plietker has
(1) (a) Shimizu, I.; Yamada, T.; Tsuji, J. Tetrahedron Lett. 1980, 3199.
(b) Tsuda, T.; Chujo, Y.; Nishi, S.-i.; Tawara, K.; Saegusa, T. J. Am. Chem.
Soc. 1980, 102, 6381. (c) Rayabarapu, D. K.; Tunge, J. A. J. Am. Chem.
Soc. 2005, 127, 13510. (d) Waetzig, S. R.; Rayabarapu, D. K.; Weaver,
J. D.; Tunge, J. A. Angew. Chem., Int. Ed. 2006, 45, 4977. (e) Waetzig,
S. R.; Tunge, J. A. J. Am. Chem. Soc. 2007, 129, 4138. (f) Weaver, J. D.;
Tunge, J. A. Org. Lett. 2008, 10, 4657. (g) Mohr, J. T.; Behenna, D. C.;
Harned, A. W.; Stoltz, B. M. Angew. Chem., Int. Ed. 2005, 44, 6924. (h)
Trost, B. M.; Bream, R. N.; Xu, J. Angew. Chem., Int. Ed. 2006, 45, 3109.
(2) (a) Guibe, F.; M’Leux, Y. S. Tetrahedron Lett. 1981, 22, 3591. (b)
Larock, R. C.; Lee, N. H. Tetrahedron Lett. 1991, 32, 6315. (c) Consiglio,
G.; Scalone, M.; Rama, F. J. Mol. Catal. 1989, 50, L11. (d) Tsuji, J.; Sato,
K.; Okumoto, H. J. Org. Chem. 1984, 49, 1341. (e) Backvall, J.-E.;
Nordberg, R. E.; Vagberg, J. Tetrahedron Lett. 1983, 24, 411.
(5) (a) Roustan, J. J.; Merour, J. Y.; Houlihan, F. Tetrahedron Lett. 1979,
39, 3721. (b) Ladoulis, S. J.; Nicholas, K. M. J. Organomet. Chem. 1985,
265, C13. (c) Xu, Y.; Zhou, B. J. Org. Chem. 1987, 52, 974. (d) Zhou, B.;
Xu, Y. J. Org. Chem. 1988, 53, 4419. (e) Eberhardt, U.; Mattern, G. Chem.
Ber. 1988, 121, 1531.
(3) Austeri, M.; Linder, D.; Lacour, J. Chem.sEur. J. 2008, 14, 5737
.
(4) Other related catalytic allylations of phenols: (a) Lopez, F.; Ohmura,
T.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 3426. (b) Evans, P. A.;
Leahy, D. K. J. Am. Chem. Soc. 2000, 122, 5012
.
10.1021/ol902291z 2009 American Chemical Society
Published on Web 11/18/2009