LITHIUM CARBONATE 1
Lithium Carbonate also reduces the selectivity of alkylation. This sequence has been
used to differentiate between the two hydroxyl groups present in
alizarin (eq 5).5
Li2CO3
O O
[554-13-2] CLi2O3 (MW 73.89)
MeI, Li2CO3
HO HO
InChI = 1/CH2O3.2Li/c2-1(3)4;;/h(H2,2,3,4);;/q;2*+1/p-
(4)
DMF, 18 h, 55 °C
2/fCO3.2Li/q-2;2m
90%
HO MeO
InChIKey = XGZVUEUWXADBQD-ULZPQPGECS
(base for dehydrohalogenation reactions and halide displace-
ments; reagent for regioselective alkylations)
O OH O OH
OH OMe
ć% ć%
MeI, Li2CO3
Physical Data: mp 723 C; bp 1310 C; d 2.11 g cm-3.
(5)
Solubility: sol cold (1 g/78 mL), hot H2O (1 g/140 mL); insol
DMF, 16 h, 50 °C
82%
alcohol, acetone.
O O
Form Supplied in: white powder; widely available.
Drying: details are available.1
1,3-Dicarbonyl compounds such as ²-keto esters or ²-diketones
are sufficiently acidic to alkylate as well (eq 6).5
Dehydrohalogenation. Lithium carbonate in refluxing
DMF is an excellent base for dehydrohalogenation reactions.
O O
LiCl in DMF caused rearrangement of the alkene to the more
O O C5H11I, Li2CO3
substituted Ä…,²-position.2 Treatment with a stronger base, lithium (6)
EtO Ph
DMF, 22 h, 80 °C
EtO Ph
carbonate, led to good yields of the less substituted enone (eq 1).
76% C5H11
Substituted tropones have been prepared in a similar manner
from alkyl-substituted tribrominated cycloheptanones (eq 2).3
Thiophenoxyphenols have shown selectivity of alkylation with
PhH O
PhH O
Li2CO3 lithium carbonate. The more acidic S H can be preferentially
Br
(1)
alkylated in deference to a phenolic O H bond.5 Using potassium
DMF, 140 °C
38%
carbonate in the same alkylation scheme gives only 4% of the
H
H
desired product.
Base Assistance. Spirocyclic ethers can be generated via
O O
Br Br
Li2CO3
Pr
intramolecular nucleophilic attack of hydroxide upon Ä„-(allyl)-
Pr Br
(2)
DMF, reflux
palladium complexes (eq 7). The attack of an external nucleophile
75%
can then be directed for either cis or trans addition, depending on
the concentration of nucleophile present.6 In the presence of 3
equiv of Li2CO3, cis migration of acetate was the only reaction
Halide Displacement. A preparation of steroidal oxetanones
observed. Conversely, the addition of 1.8 equiv of chloride ion
has been reported using Li2CO3 in refluxing DMF. It was found
causes chloride to be added from the face opposite the metal.
that either the cis or the trans bromides can give the Ä…-oxetanone
in good yield (eq 3).4
O
5% Pd(OAc)2
3.0 equiv Li2CO3, 24 h
AcO
86%
( )2OH
Li2CO3
(7)
>98% trans
O (3)
DMF, reflux
O
5% Pd(OAc)2
AcO Br AcO
69%
OH
O O
1.8 equiv LiCl, 24 h
73%
Cl
>99% cis
Alkylations. Lithium carbonate used in conjunction with
DMF and various alkylating agents has been found to regios-
Related Reagents. Lithium Carbonate Lithium Bromide;
electively alkylate bisphenolic, 1,3-dicarbonyl, and thiol sub-
Potassium Carbonate; Sodium Carbonate.
strates that contain hydrogens that are more acidic than phenol
(pKa H" 8).5 It has been determined that phenolic compounds con-
taining electron-withdrawing groups alkylate at either the ortho or
1. Inorg. Synth. 1939, 1, 1.
para positions exclusively (eq 4). Attempts to use other bases such
2. House, H. O.; Bashe, II, R. W., J. Org. Chem. 1965, 30, 2942.
as Potassium Carbonate or Sodium Carbonate showed a loss of
3. (a) Jones, G., J. Chem. Soc. (C) 1970, 1230.(b) Collington, E. W.; Jones,
selectivity. Using more reactive alkylating agents such as propar-
G. J. Chem. Soc. (C) 1969, 2656.(c) Collington, E. W.; Jones, G. 1968,
gyl bromide (see under Propargyl Chloride) or Benzyl Bromide 958.
Avoid Skin Contact with All Reagents
2 LITHIUM CARBONATE
4. (a) Hanna, R.; Maalouf, G.; Muckensturm, B., Tetrahedron 1973, 29, 6. Bäckvall, J. E.; Andersson, P. G., J. Org. Chem. 1991, 56, 2274.
2297.(b) Rowland, A. T.; Bennett, R. J.; Shoupe, T. S., J. Org. Chem.
1968, 33, 2426.
Dennis Wright & Mark C. McMills
5. Wymann, W. E.; Davis, R.; Patterson, J. W.; Pfister, J., Synth. Commun.
1988, 18, 1379. Ohio University, Athens, OH, USA
A list of General Abbreviations appears on the front Endpapers