[554-13-2] · CLi2O3 · Lithium Carbonate · (MW 73.89)
(base for dehydrohalogenation reactions and halide displacements; reagent for regioselective alkylations)
Physical Data: mp 723 °C; bp 1310 °C; d 2.11 g cm-3.
Solubility: sol cold (1 g/78 mL), hot H2O (1 g/140 mL); insol alcohol, acetone.
Form Supplied in: white powder; widely available.
Lithium carbonate in refluxing DMF is an excellent base for dehydrohalogenation reactions. LiCl in DMF caused rearrangement of the alkene to the more substituted a,b-position.2 Treatment with a stronger base, lithium carbonate, led to good yields of the less substituted enone (eq 1). Substituted tropones have been prepared in a similar manner from alkyl-substituted tribrominated cycloheptanones (eq 2).3
A preparation of steroidal oxetanones has been reported using Li2CO3 in refluxing DMF. It was found that either the cis or the trans bromides can give the a-oxetanone in good yield (eq 3).4
Lithium carbonate used in conjunction with DMF and various alkylating agents has been found to regioselectively alkylate bisphenolic, 1,3-dicarbonyl, and thiol substrates that contain hydrogens that are more acidic than phenol (pK
1,3-Dicarbonyl compounds such as b-keto esters or b-diketones are sufficiently acidic to alkylate as well (eq 6).5
Thiophenoxyphenols have shown selectivity of alkylation with lithium carbonate. The more acidic S-H can be preferentially alkylated in deference to a phenolic O-H bond.5 Using potassium carbonate in the same alkylation scheme gives only 4% of the desired product.
Spirocyclic ethers can be generated via intramolecular nucleophilic attack of hydroxide upon p-(allyl)palladium complexes (eq 7). The attack of an external nucleophile 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 observed. Conversely, the addition of 1.8 equiv of chloride ion causes chloride to be added from the face opposite the metal.
Lithium Carbonate-Lithium Bromide;
Dennis Wright & Mark C. McMills
Ohio University, Athens, OH, USA