Lithium chloride esters

The equihbrium shown in equation 3 normally ties far to the left. Usually the water formed is removed by azeotropic distillation with excess alcohol or a suitable azeotroping solvent such as benzene, toluene, or various petroleum distillate fractions. The procedure used depends on the specific ester desired. Preparation of methyl borate and ethyl borate is compHcated by the formation of low boiling azeotropes (Table 1) which are the lowest boiling constituents in these systems. Consequently, the ester—alcohol azeotrope must be prepared and then separated in another step. Some of the methods that have been used to separate methyl borate from the azeotrope are extraction with sulfuric acid and distillation of the enriched phase (18), treatment with calcium chloride or lithium chloride (19,20), washing with a hydrocarbon and distillation (21), fractional distillation at 709 kPa (7 atmospheres) (22), and addition of a third component that will form a low boiling methanol azeotrope (23). 

Several derivatives of cellulose, including cellulose acetate, can be prepared in solution in dimethylacetamide—lithium chloride (65). Reportedly, this combination does not react with the hydroxy groups, thus leaving them free for esterification or etherification reactions. In another homogeneous-solution method, cellulose is treated with dinitrogen tetroxide in DMF to form the soluble cellulose nitrite ester this is then ester-interchanged with acetic anhydride (66). With pyridine as the catalyst, this method yields cellulose acetate with DS < 2.0. 

Lithium aluminum hydride (LiAlH4) is the most powerful of the hydride reagents. It reduces acid chlorides, esters, lactones, acids, anhydrides, aldehydes, ketones and epoxides to alcohols amides, nitriles, imines and oximes to amines primary and secondary alkyl halides and toluenesulfonates to... 

Activity is also retained when the hydroxyl group at the 21 position is replaced by chlorine. Reaction of corticoid 44 with methanesulfonyl chloride proceeds preferentially at the 21-hydroxyl (45) due to the hindered nature of the 11-alcohol. Replacement of the mesylate by means of lithium chloride in DMF affords clobetasol propionate (46) a similar sequence starting with the 17- butyrate ester 47, via mesylate 48, should give clobetasone butyrate, (49) [11]. 

Metal halide salts other than sodium iodide have been used sparsely to prepare halodeoxy sugars from sulfonate esters. Lithium chloride (107) and lithium bromide (33) have found limited application. Potassium fluoride (dihydrate) in absolute methanol has been used (51, 52) to introduce fluorine atoms in terminal positions of various D-glucose derivatives. The reaction is conducted in sealed tube systems and requires... 

The palladium-catalyzed cross-coupling reaction featured in this procedure occurs under neutral conditions in the presence of many synthetically useful functional groups (e.g. alcohol, ester, nitro, acetal, ketone, and aldehyde). The reaction works best in N,N-dimethylformamide with bis(triphenylphosphine)palladium(ll) chloride, PdCI2(PPh3)2, as the catalyst. Lithium chloride is added to prevent decomposition of the catalyst.143 13 It is presumed that conversion of the intermediate aryl palladium triflate to an aryl palladium chloride is required for the transmetallation step to proceed.9... 

Step (a) To a 500 mL round bottom flask containing a stir bar was added shell reagent (Y) G = 3.5 methyl ester PAMAM dendrimer, EDA core, (32 g, 2.6 x 10-3 mol, 164 mmol ester, 25 equivalents per core dendrimer (X) and 32 g of methanol. This mixture was stirred until homogeneous. To this mixture was added lithium chloride (7 g, 166 mmol, 1 equivalent per ester) and stirred until homogenous. To this mixture was added (drop-wise) PAMAM dendrimer, EDA core, G = 6 (6 g, 1.0 x 10-4 mol) in 20g of methanol in 10 min. This mixture was warmed to 25 °C and placed in a constant temperature bath at 40 °C for 25 days. 

N-Allenylazetidinone 181 rearranges to cephalosporin 182 in the presence of lithium chloride (Eq. 13.62) [70], This is a very unusual reaction that is presumed to be initiated by chloride ion-induced cleavage of the disulfide to give sulfenyl chloride 183. Thiolate attack at the allene sp carbon atom of 183 generates ester enolate 184, which cyclizes to 182. The reactivity of the allene function in 181 ensures the success of the reaction. 

One benzyl group may be removed from (XVI) by two methods (1) quatemization in which a tertiary base attacks one benzyl group yielding the quaternary benzylammonium salt of the di-phosphate1 (XVII) (see also p. 101) or (2) the use of a salt (e.g. lithium chloride).2 In both (1) and (2) the mono-debenzylated ester produced is an anion, and would therefore tend to resist a second debenzylation process which requires the formation of a doubly-charged anion. 

Acid chlorides, R(Ar)COCl, are reduced to R(Ar)CHO by Hj/Pd(S), a moderate catalyst that does not reduce RCHO to RCHjOH (Rosenmund reduction). Acid chlorides, esters (R(Ar)COOR), and nitriles (RC N) are reduced with lithium tri-t-butoxyaluminum hydride, LiAlH[OC(CH3)3]j, at very low temperatures, followed by HjO. The net reaction is a displacement of X by H",... 

Spiroannelation. A new method for intramolecular spirocyclizalion involves decarboxylation of w-halogeno-j8-keto esters with lithium chloride in HMPT at 125— 140°. The method appears to be fairly general.1 Examples ... 

Esters are more difficult to reduce, and usually, no reaction takes place with sodium borohydride. However, the potassium borohydride/lithium chloride system was found to reduce esters under microwave conditions in a solvent-free reaction33. The reactions are generally completed in 2-8 min and provide the corresponding alcohols in 55-95% yield (Scheme 4.13). 

Feng, J.C., Liu, B., Dai, L., Yang, X.T. and Tu, S.J., Microwave assisted solid reaction reduction of esters to alcohols by potassium boro hydride-lithium chloride, Synth. Commun., 2001, 31, 1875-1877. 

Peptide aldehydes 1 can be synthesized effectively by the oxidation of peptide alcohols 15, which are readily available without racemization by reduction of peptide esters 9 with sodium borohydride-lithium chloride (Scheme 5). The peptide alcohols 15 can be readily oxidized to afford enantiomerically pure aldehydes using Parikh-Doering or Dess-Martin reagents. This route is less popular than the previously described reductive methods due to (1) the sensitivity of the aldehydes to further oxidation, (2) racemization under the reaction conditions, and (3) instability of the products under the reaction conditions. 

Keywords ester, potassium borohydride-lithium chloride, microwave irradiation, alcohol... 

Potassium borohydride (1.0 g, 20 mmol), anliydrous lithium chloride (0.8 g, 20 mmol) were thoroughly mixed in a mortar and transferred to a flask (100 mL) connected with reflux equipment, then dry THF (10 mL) was added and the mixture was heated to reflux for 1 h. After cooling, the ester (10 mmol) was added and stirred for 0.5 h at room temperature, then the THF was removed under reduced pressure. After the mixture was irradiated by microwave for 2-8 min, the mixture was cooled to room temperature, water (20 mL) was added, extracted with ether (3 x 15 mL), dried with magnesium sulfate, and evaporated to give the crude product, which was purified by crystallization, distillation or column chromatography. 

The iodo derivative is a useful intermediate for the preparation of a wide variety of different types of compounds. Primary mesyl esters also react with sodium iodide in acetone, but the selectivity of this cleavage is less because of the greater reactivity of secondary mesyl esters. oa( ) Methyl 2,3,4-tri-0-acetyl-6-0-mesyl-a-D-glucopyranoside is converted into methyl 2,3,4,6-tetra-O-acetyl-a-D-glucopyranoside with acetic anhydride and potassium acetate. Replacements of a primary mesyloxy group with fluorine by use of potassium fluoride in methanol,106 with chlorine by use of lithium chloride,102 and with pyridine to form a pyri-dinium deoxy derivative,106 have been reported. Primary tosyloxy groups have been replaced by hydrogen,106 by thiocyanate,107 and by... 

Lithium borohydride is intermediate in activity as a reducing agent between lithium aluminium hydride and sodium borohydride. In addition to the reduction of aldehydes and ketones it will readily reduce esters to alcohols. It can be prepared in situ by the addition of an equivalent quantity of lithium chloride to a 1m solution of sodium borohydride in diglyme. Lithium borohydride should be handled with as much caution as lithium aluminum hydride. It may react rapidly and violently with water contact with skin and clothing should be avoided. 

Reduction by mild reducing agents converts acyl chlorides, esters, and nitrites into aldehydes. The reducing agents of choice are usually lithium tri-tert-butoxy aluminum hydride (LATB—H) and diisobuty-laluminum hydride (DIBAL—H). Following are the structures for these compounds ... 

Nitrobenzene-p-sulphonyI)neopine has been converted into the 6/3-chloro- and 6j0-bromo-6-deoxy-compounds by heating with lithium chloride and bromide,154 and the 6-O-methanesulphonyl analogue gives the same products together with the A6-8-deoxy-compound, which is the sole product when the ester is heated with sodium iodide.155 2-Nitromorphine and 2-nitrocodeine have been reduced to the 2-amino-compounds in 60% and 81% yield respectively.156... 

Methyl esters 333 that are activated toward decarboxylation by a C-2-ethoxycarbonyl group and tethered by an alkyl chain to an acrylate Michael-acceptor undergo chemoselective S] [2-dealkylation of the methyl ester, decarboxylation and cyclization upon exposure to lithium chloride in DMEU, affording tetrahydropyrans in excellent yield and diastereoselectivity (Equation 142) <1998JOC144>. 

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