Lithium iodide esters

Earlier catalysts were based on cobalt, iron, and nickel. However, recent catalytic systems involve rhodium compounds promoted by methyl iodide and lithium iodide (48,49). Higher mol wt alkyl esters do not show any particular abiUty to undergo carbonylation to anhydrides. 

Cleavage of Carboxylic Esters With Lithium Iodide... 

Carboxylic esters where R is methyl or ethyl can be cleaved by heating with lithium iodide in refluxing pyridine or a higher boiling amine. " The reaction is useful where a molecule is sensitive to acid and base (so that 10-10 cannot be used) or where it is desired to cleave selectively only one ester group in a molecule containing two or more. For example, refluxing O-acetyloleanolic acid methyl ester... 

In summary, we have examined several new methods for cleaving ester groups in poly(styrene-b-alkyl methacrylates). Short blocks of methyl methacrylate are very difficult to hydrolyze, but can be cleaved with reagents such as lithium iodide and potassium trimethylsilanolate. These latter reagents, however, result in side-reactions which appear to crosslink the polymer. 

Methyl esters react more rapidly with lithium iodide than do ethyl esters, which in turn react more rapidly than esters of secondary alcohols. On the other hand, i-butyl esters are cleaved very readily with a catalytic amount of lithium iodide. 

Alternatively, epoxide (3R,5S)-14 was opened regioselectively with lithium iodide on silica [29], The crude product was immediately subjected to acetonide protection, which afforded the desired iodide sy -(3R,5S)-13 with a 58% yield (44% from syn-(3R,5S)-5a Scheme 2.2.7.7). Epoxide (3R,5S)-14 was easily obtained from dihydroxy ester syn-(3R,5S)-5a by treatment with DBU (66% yield) [11]. Treatment of sy -(3R,5S)-5a with LiCN in CH2CI2 gave nitrile (3R,5R)-15 in almost quantitative yield [21]. 

The concave acids 38 and the esters 39 could be interconverted. Reaction of the acids 38 with diazomethane led to the methyl esters 39. 8 2 dealkylation of the esters 39 by lithium iodide in pyridine gave the acids 38 [27]. 

Cleavage of Carboxylic Esters with Lithium Iodide lodo-de-acyloxy-substitution... 

The solvents utilized were all analytical grade reagents further purified by distillation. A-(3-Triethoxysilyl)-propanamine (APTES), nonanedioic acid monomethyl ester, 12-nitro-dodecanoic acid, octadecanoic acid, octadecylamine, and lithium iodide were Aldrich samples and were used as received. Silicon wafers were supplied by International Wafer Service, Palo Alto, CA. 

Chemically cleaned silicon wafers (lxl cm2 pieces) were treated with 9-[AM3-triethoxysilylpropyl)amino]-9-oxononanoic acid methyl ester in toluene (20 ml of a 2% solution) at room temperature under nitrogen overnight. The wafers were then thoroughly washed with chloroform, methanol, and acetone in that order, and suspended in dimethylformamide (DMF 10 ml) containing lithium iodide (1 g). The mixture was refluxed for several hours. The wafers were recovered and washed several times with distilled water, once with sodium carbonate (1% aq., 10 ml) and again with distilled water. Finally, the wafers were rinsed with acetone and stored in a vacuum desiccator under nitrogen. 

ESTERS Sodium benzeneselenolate. ETHERS Boron tribromide-Sodium iodide-15-Crown-5. Boron trifluoride etherate. Ferric chloride-Silica. Lithium iodide. Silicon(IV) chloride-Sodiuiu iodide. Sodium iodide-Pivaloyl chloride. 2,4,4,6-Tetrabromocyclohexadiene. Trichloro(methyl)silane. 

Fig. 2.2. Cleavage of aromatic methyl ether using Sn2 reactions. In the dipolar aprotic solvent DMF, thiolate and chloride ions are particularly good nucleophiles for want of solvation through hydrogen bonding. In pyri-dinium hydrochloride a similar effect occurs because for each chloride only one N5 —H5 group is available for hydrogen bonding. The same increase in nucleophilicityin a dipolar aprotic solvent is used to cleave /i-ketomethyl esters with lithium iodide in DMF (cf. Figure 13.29).

Diethyoxymethyldiphenylphosphine oxide. KETENE THIOACETALS Lithium iodide. a-KETO aldehydes Nafion-H. a-KETO esters f-Butyl hydroperoxide. Cy-anotrimethylsilane. 1,2-Diethoxy-1,2-disi-lyloxyethane. Trimethylphosphonoglyco-late. 

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