[10377-51-2] · ILi · Lithium Iodide · (MW 133.84)
Physical Data: mp 449 °C; bp 1180 °C; d 4.076 g cm-3.
Solubility: 165 g/100 mL H2O (20 °C); 433 g/100 mL H2O (80 °C); 251 g/100 mL EtOH (20 °C); 343 g/100 mL MeOH (20 °C); 43 g/100 mL acetone (18 °C); very sol NH4OH.
Form Supplied in: anhydrous white solid or as the hydrate.
Preparative Methods: the anhydrous salt of high purity can be prepared from lithium hydride and iodine in ether.5
Purification: crystallized from hot H2O (0.5 mL g-1) by cooling in CaCl2-ice or from acetone. LiI is dried for 2 h at 120 °C (0.1 mmHg, P2O5) before use.
Handling, Storage, and Precautions: for best results, LiI should be dried prior to use in anhydrous reactions.
In the presence of amine bases, LiI has been extensively used as a mild reagent for the chemoselective cleavage of methyl esters (eq 1).6 Decarboxylation of methyl esters usually occurs when an electron-withdrawing group is present at the a-position of the ester (eq 2).7 Ester-type glycosyl linkages of acidic tri- and diterpenes can also be selectively cleaved under these conditions.8 Aryl methyl ethers can be demethylated to afford the corresponding phenols upon heating with LiI and s-collidine.9
1,2-Oxiranes are readily opened by LiI and a Lewis acid to produce iodohydrins (eq 3).4 Conversely, 1-oxaspiro[2.2]pentanes and 1-oxaspiro[3.2]hexanes give rise to bond migration products.10 b-Vinyl-b-propiolactone is efficiently opened by LiI to produce the corresponding substituted allyl iodide (eq 4).11
LiI has been used as a source of iodide in nucleophilic substitution and addition reactions. Primary alcohols have been directly converted to alkyl iodides upon treatment with a mixture of Triphenylphosphine, Diethyl Azodicarboxylate, and LiI.3 Tertiary alcohols can be converted into tertiary alkyl iodides upon treatment with Hydrogen Iodide in the presence of LiI.12
(Z)-3-Iodopropenoates and -propenoic acids have been synthesized stereoselectively by the reaction of LiI and propiolates or propiolic acid.13
LiI was shown to efficiently catalyze the Michael addition of b-dicarbonyl compounds,14 and the intramolecular allylsilane addition to imines to produce 4-methylenepiperidine derivatives (eq 5).15
The syn/anti selectivity in the reduction of b-alkoxy ketones is drastically increased by the addition of LiI (eq 6).17
The addition of Lithium Bromide and LiI was shown to enhance the rate of organozinc formation from primary alkyl chlorides, sulfonates, and phosphonates, and zinc dust.18 Beneficial effects of LiI addition have also been reported for Heck-type coupling reactions19 and in conjugate addition to chiral vinyl sulfoximines.20
The (E)/(Z) alkenic ratio in Wittig-type alkenations was shown to be dependent on the amount of Li salt present.21
a-Halo ketones are reduced to the corresponding ketones upon treatment with a mixture of LiI and Boron Trifluoride Etherate.22
André B. Charette
Université de Montréal, Québec, Canada