POTASSIUM CARBONATE 1
O NH2 O
Potassium Carbonate1 O
Na2Fe(CN)5NO
(3)
Me2N Me2N
K2CO3, H2O
OH 61%
K2CO3
O NH2 O OH
Na2Fe(CN)5NO
(4)
[584-08-7] CK2O3 (MW 138.21)
EtO EtO
K2CO3, H2O
InChI = 1/CH2O3.2K/c2-1(3)4;;/h(H2,2,3,4);;/q;2*+1/p-2/fCO3.
58%
2K/q-2;2m
InChIKey = BWHMMNNQKKPAPP-VPFIEVHZCO
Reactions of 1,3-Dicarbonyl Compounds. The enolate of ²-
(inorganic base used in the alkylation of phenols2 and 1,3-dicarbo- keto esters can be alkylated in a procedure developed by Claisen8
nyl compounds;7 generation of sulfur12 and phosphorus ylides;13
that is analogous to the alkylation of phenols. The ²-keto ester and
also used to dry organic solvents16)
alkylating agent are combined with K2CO3 in acetone and the
reaction heated to reflux. The reaction is useful for the C-alkylation
ć%
Physical Data: mp 891 C; d 2.43 g cm-3; hygroscopic until
of substrates. In the case of ethyl 2-oxocyclopentanecarboxylate9
16.4% water is absorbed; pH of saturated aqueous solution is
the reaction gave good yields and high selectivity for C-alkylation
11.6.
with unobstructed alkylating agents (eq 5).
ć%
Solubility: 1.12 g mL-1 in water at 20 C; practically insol alco-
hol.
R
K2CO3
Form Supplied in: white solid; widely available. Use in form
CO2Et CO2Et CO2Et
+ RX +
acetone
supplied for best results.
(5)
ć%
O O OR
Purification: crystallize from water 70 C; dry over H2SO4.
Handling, Storage, and Precautions: keep in a tightly sealed con-
RX C-alkylation (%) O-alkylation (%)
tainer; avoid inhalation.
MeI 100 <1
(MeO)2SO2 100 <1
H2C=CHCH2Br 91 <1
Alkylation of Phenols. The mildly basic nature of this reagent
BrCH2CO2Et 92 <1
makes it ideal for the selective deprotonation of organic acids.
i-PrI 78 18
This property makes K2CO3 a useful reagent for the alkylation of
PhCH2OCH2Cl 49 21
phenols. The procedure2 for phenol alkylation involves dissolving
the phenol and alkylating agent in acetone with excess K2CO3 The reagent also shows good selectivity in the monoalkylation
added as an insoluble component (eq 1). The reaction is run at
of ²-dicarbonyl compounds. The reaction of 2-chloro-2-methyl-
reflux. Workup consists of removal of solvent and addition of
proponal with malonic esters in THF or ether gives good yield
water. The product is isolated by either extraction or filtration.
of the monoalkylated malonic ester (eq 6).10
Popular alternative solvents are DMF3 and MeCN.4 If the aqueous
CO2Et
solution needs to be neutralized, it is convenient to remove excess K2CO3
+ (6)
K2CO3 via filtration before solvent removal and subsequent water
Cl CHO (EtO2C)2HC CHO
THF or ether
CO2Et
addition. 60%
OH O
Aldehydes can be reacted with 1,3-dicarbonyl compounds in
NO2 NO2
THF to give Ä…,²-unsaturated carbonyl compounds with good (Z/E)
K2CO3
+ (1)
Br selectivity (eq 7).11
acetone
80%
O O
K2CO3
CCl3 CHO + (7)
Cl3C COMe
Sulfides can also be alkylated using K2CO3 in DMF, as demons-
THF
74%
trated in the shell closure reaction used to capture guests within
100% (Z)
linked anisyl moieties.5
The reagent is also useful for the generation of intramole-
Hydrolysis Reactions. Ester hydrolysis using K2CO3 in
cular Michael addition products with excellent stereoselectivity
MeOH was found to give clean conversion to the allylic alcohol
(eq 8).12
(eq 2).6
CO2Et
O CO2Et O
Ph Ph
2.5% K2CO3
K2CO3
O (8)
ethanol
(2)
O
MeOH
45%
N N
H
AcO HO
74%
H H
Ph Ph
When amides that contain Ä…,²-amino alcohols undergo diazo- Generation of Phosphorus Ylides. Wittig reactions can
tization followed by treatment with aqueous K2CO3,7 they are be done either under heterogeneous (water 1,4-dioxane) condi-
cleanly converted to the epoxide (eq 3), while the ²-amino ester tions13 or more conveniently using 18-crown-6 as a phase-
gives the corresponding alcohol (eq 4). transfer catalyst (see Potassium Carbonate 18-Crown-6).14 The
Avoid Skin Contact with All Reagents
2 POTASSIUM CARBONATE
phase-transfer conditions give alkenes in good yields with a pref-
1. Fieser & Fieser 1975, 5, 552.
erence for the (E)-isomer (eq 9). The procedure involves the com-
2. Allen, C. F.; Gates, J. W. Jr., Org. Synth., Coll. Vol. 1955, 3, 140.
bination of alkylphosphonium salt, K2CO3, aldehyde, and 18-
3. Sherman, J. C.; Knobler, C. B.; Cram D. J., J. Am. Chem. Soc. 1991, 113,
Crown-6 in either CH2Cl2 or THF. The solvent is removed, prod-
2194.
uct extracted with petroleum ether, and filtered through silica gel.
4. Davis, R.; Muchowski, J. M., Synthesis 1982, 987.
5. Bryant, J. A.; Blanda, M. T.; Vincenti, M.; Cram, D. J., J. Am. Chem.
+ K2CO3, 18-crown-6
R1CHO + Ph3PCH2R2 R1CH=CHR2 (9) Soc. 1991, 113, 2167.
CH2Cl2 or THF
X
6. Martin, S. F.; Campbell, C. L., Tetrahedron Lett. 1987, 28, 503.
7. McGarvey, G. J.; Kimura, M., J. Org. Chem. 1986, 51, 3913.
R1 R2 (E) %
8. Methoden Org. Chem. (Houben-Weyl) 1952, 8, 602.
9. Barco, A.; Benetti, S.; Pollini, G. P., Synthesis 1973, 316.
Ph Ph 70
Ph Me 78
10. Takeda, A.; Sadao, T.; Oota, Y., J. Org. Chem. 1973, 38, 4148.
Et Ph 75
11. Tsuboi, S.; Uno, T.; Takeda, A., Chem. Lett. 1978, 1325.
12. Stork, G.; Taber, D. F.; Marx, M., Tetrahedron Lett. 1978, 2445.
13. Le Bigot, Y.; Delmas, M.; Gaset, A., Synth. Commun. 1982, 12, 107.
Generation of Sulfur Ylides. ²-Ketosulfonium salts react
14. Boden, R. M., Synthesis 1975, 783.
with K2CO3 to generate the corresponding ylide. Ä…-Methylthio
15. Ogura, K.; Furukawa, S.; Tsuchihashi, G., J. Am. Chem. Soc. 1980, 102,
ketones are reacted with allylic halides to afford sulfonium salts
2125.
that are reacted with aqueous K2CO3 to generate a sulfur ylide15
16. Gordon, A. J.; Ford, R. A. The Chemist s Companion: A Handbook of
that can undergo [2,3]-sigmatropic rearrangement (eq 10).
Practical Data, Techniques, and References, Wiley: New York, 1972;
p 445.
O
2M K2CO3
Br Me
+ (10)
S Kurt D. Deshayes
O SMe Bowling Green State University, Bowling Green, OH, USA
A list of General Abbreviations appears on the front Endpapers