C O MMU N I C A T I O N S
Scheme 2
Although at this point no rigorous mechanistic studies have been
conducted, a working hypothesis has evolved based on the observed
products and the known behavior of metallacarbenes (Scheme 2).
Presumably, a silver carbenoid 17 is formed on reaction of the
catalyst with ethyl diazoacetate (4), which then reacts with the halide
to form a ylide (18). In the absence of a â-hydrogen, a 1,2-shift of
the alkyl moiety occurs to provide the rearrangement product (18a
f 6, 14, 15). If a â-hydrogen is present, elimination occurs to
provide the corresponding ethyl haloacetate (18b f 16) and alkene
(
19).
In summary, we have identified a novel silver-catalyzed process
involving carbene precursors and aliphatic carbon-halogen bonds.
Table 2. Dependence on Catalyst
3
3
This transformation results in the formation of a new sp -sp
carbon-carbon bond and the net migration of a halide atom. Further
attempts to extend this chemistry as well as additional applications
of this catalyst are under investigation in our laboratories.
Acknowledgment. This work has been supported by the Robert
A. Welch Foundation.
Supporting Information Available: Experimental procedures and
spectroscopic data for all of the compounds (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
a
1
Not determined; dimers were the only observed product in the H NMR
of the crude reaction mixture.
References
this result, a number of chloroalkanes were surveyed, including a
number of common chlorinated solvents and chloroalkanes (Table
(1) Grushin, V. V.; Alper, H. Top. Organomet. Chem. 1999, 3, 193.
(2) Luh, T.-Y.; Leung, M.-k.; Wong, K.-T. Chem. ReV. 2000, 100, 3187.
1
, 7a-13a), as substrates for this insertion.
(3) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 2002, 41, 4176.
In general, two reaction pathways were observed: either insertion
(
4) Gordon, A. J.; Ford, R. A. The Chemist’s Companion; Wiley: New York,
into the C-Cl bond or 1,1-hydrochlorination (Table 1). For
example, at room temperature, a mixture of CHCl and EDA in
the presence of 5 mol % [HB(3,5-(CF Pz) ]Ag(THF) afforded
HClC(CO Et)CCl H (14a) in 60% yield. When attempts were made
1972; p 113.
(5) March, J. AdVanced Organic Chemistry; Wiley: New York, 1992; p 357.
3
(
6) Terao, J.; Watanabe, H.; Ikumi, A.; Kuniyasu, H.; Kambe, N. J. Am. Chem.
3
)
2
3
Soc. 2002, 124, 4222.
2
2
(7) Urry, W. H.; Eisner, J. R.; Wilt, J. W. J. Am. Chem. Soc. 1957, 79, 918.
to extend this reaction to primary, secondary, or tertiary alkyl
chlorides, rather than the expected insertion product, ethyl chloro-
acetate 16a, the net addition of H-Cl to the carbene, was obtained
(8) Urry, W. H.; Eisner, J. R. J. Am. Chem. Soc. 1952, 74, 5822.
9) Urry, W. H.; Eisner, J. R.; Wilt, J. W. J. Am. Chem. Soc. 1951, 73, 2977.
10) Urry, W. H.; Wilt, J. W. J. Am. Chem. Soc. 1954, 76, 2594.
(
(
(
11) Migita, T.; Ando, W.; Kondo, S.; Matsuyama, H.; Kosugi, M. Nippon
(see Scheme 2). Successful experiments with the analogous bromo
Kagaku Zasshi 1970, 91, 374.
(
12) Dias, H. V. R.; Lu, H.-L.; Ratcliff, R. E.; Bott, S. G. Inorg. Chem. 1995,
derivative (Table 1, 7b-10b, 12b) suggest that this reaction is not
limited to chloroalkanes.
To establish whether this reaction was restricted to complex
34, 1975.
(
13) Dias, H. V. R.; Lu, H.-L.; Goh, T. K. H. H.; Polach, S. A.; Browning, G.;
Lovely, C. J. Organometallics 2002, 21, 1466 and references therein.
(
(
(
14) Dias, H. V. R.; Jin, W. Inorg. Chem. 1996, 35, 3687 and references therein.
15) Dias, H. V. R.; Jin, W. Inorg. Chem. 2000, 39, 815.
16) Ayers, A. E.; Dias, H. V. R. Inorg. Chem. 2002, 41, 3259.
[
HB(3,5-(CF
3
)
2
Pz)
3
]Ag(THF), other silver(I) salts were investigated.
O or AgOTf gave very
It was found that silver salts such as Ag
2
poor yields of the insertion product with chloroform under condi-
tions similar to those routinely employed (Table 2). Interestingly,
the silver salt of the nonfluorinated ligand [HB(3,5-Me Pz) ]Ag
2 3
(17) Where [(n-Pr) ATI] ) N-(n-propyl)-2-(n-propylamino)troponiminate.
2
(18) Catalytic properties of copper complexes containing nonfluorinated tris-
(
pyrazolyl)borates are also of significant current interest. See, for
example: Caballero, A.; D ´ı az-Requejo, M. M.; Belderra ´ı n, T. R.; Nicasio,
did not provide any product resulting from C-Cl insertion or from
M. C.; Trofimenko, S.; P e´ rez, P. J. J. Am. Chem. Soc. 2003, 125, 1446.
the elimination pathway.22 Either carbene dimers (diethyl fumarate
(19) Dias, H. V. R.; Jin, W. Inorg. Chem. 1996, 35, 267. Dias, H. V. R.; Wang,
Z.; Jin, W. Inorg. Chem. 1997, 36, 6205.
and maleate) or unreacted EDA were recovered as major products
(20) Dias, H. V. R.; Polach, S. A. Inorg. Chem. 2000, 39, 4676.
from these mixtures. It was further found that the commonly
employed rhodium acetate23 does not catalyze the formation of
products derived from C-Cl insertion; only maleate and fumarate
are observed.
(21) It has been found that this complex catalyzes the addition of carbenes to
aromatic rings to provide a net Buchner reaction product. Details of this
study will be reported elsewhere. Dias, H. V. R.; Browning, R. G.;
Diyabalanage, H. V. K.; Polach, S. A.; Lovely, C. J., manuscript in
preparation.
(
22) Effendy; Lobbia, G. G.; Pettinari, C.; Santini, C.; Skelton, B. W.; White,
A. H. Inorg. Chim. Acta 2000, 308, 65. It is conceivable that this lack of
reactivity is due to the attenuated stability of the nonfluorinated complex.
The use of silver salts with diazo compounds is well known,
24
particularly in the Wolff rearrangement, although normally stoi-
chiometric quantities are employed. It has also been reported that
(
23) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic Methods for
Organic Synthesis with Diazo Compounds; Wiley: New York, 1998.
Ag
2
O has been utilized in a process to transfer the -C(N
2 2
)CO Et
(24) Kirmse, W. Eur. J. Org. Chem. 2002, 2193.
(25) Schoellkopf, U.; Rieber, N. Chem. Ber. 1969, 102, 488.
moiety to bromo and iodo reagents. It is, however, a silver salt
(26) Schoellkopf, U.; Rieber, N. Angew. Chem., Int. Ed. Engl. 1967, 6, 261.
metathesis reaction, and it is believed to proceed via the
5,26
AgC(N
2
)CO
2
Et intermediate.2
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