Phase transfer alcohols

Acetylene is also protected as propargyl alcohol (300)[2H], which is depro-tected by hydrolysis with a base, or oxidation with MnOi and alkaline hydrolysis. Sometimes, propargyl alcohols are isomerized to enals. Propargyl alcohol (300) reacts with 3-chloropyridazine (301) and EtiNH to give 3-diethylami-noindolizine (303) in one step via the enal 302[2I2]. Similarly, propargyl alcohol reacts with 2-halopyridines and secondary amines. 2-Methyl-3-butyn-2-ol (304) is another masked acetylene, and is unmasked by treatment with KOH or NaOH in butanol[205,206,213-2l5] or in situ with a phase-transfer cata-lyst[2l6]. 

Pyrrohdinone can be alkylated by reaction with an alkyl haUde or sulfate and an alkaline acid acceptor (63,64). This reaction can be advantageously carried out with a phase-transfer catalyst (65). Alkylation can also be accompHshed with alcohols and either copper chromite or heterogenous acid catalysts... 

Nucleophilic Reactions. Useful nucleophilic substitutions of halothiophenes are readily achieved in copper-mediated reactions. Of particular note is the ready conversion of 3-bromoderivatives to the corresponding 3-chloroderivatives with copper(I)chloride in hot /V, /V- dim ethyl form am i de (26). High yields of alkoxythiophenes are obtained from bromo- and iodothiophenes on reaction with sodium alkoxide in the appropriate alcohol, and catalyzed by copper(II) oxide, a trace of potassium iodide, and in more recent years a phase-transfer catalyst (27). 

Reactions of the Side Chain. Benzyl chloride is hydrolyzed slowly by boiling water and more rapidly at elevated temperature and pressure in the presence of alkaHes (11). Reaction with aqueous sodium cyanide, preferably in the presence of a quaternary ammonium chloride, produces phenylacetonitrile [140-29-4] in high yield (12). The presence of a lower molecular-weight alcohol gives faster rates and higher yields. In the presence of suitable catalysts benzyl chloride reacts with carbon monoxide to produce phenylacetic acid [103-82-2] (13—15). With different catalyst systems in the presence of calcium hydroxide, double carbonylation to phenylpymvic acid [156-06-9] occurs (16). Benzyl esters are formed by heating benzyl chloride with the sodium salts of acids benzyl ethers by reaction with sodium alkoxides. The ease of ether formation is improved by the use of phase-transfer catalysts (17) (see Catalysis, phase-thansfer). 

ClCH20Me, CH2CI2, NaOH-H20, Adogen (phase-transfer cat.), 20°, 20 min, 80-95% yield. This method has been used to protect selectively a phenol in the presence of an alcohol. ... 

AcCl, NaOH, dioxane, Bu4N HSO, 25°, 30 min, 90% yield. Phase-transfer catalysis with tetra-n-butylammionium hydrogen sulfate effects acylation of sterically hindered phenols and selective acylation of a phenol in the presence of an aliphatic secondary alcohol. 

The synthesis of fluoroalkyl and chloroalkyl fluoromethyl ketones is achieved by oxidation of the corresponding alcohols by sodium dichromate and sulfunc acid in methylene chlonde in the presence of a phase transfer catalyst [49] (equation 45)... 

NaH, /7-MeOQH4CH2Br, DMF, —5°, 1 h, 65%. Other bases, such as BuLi, ° dimsyl potassium," and NaOH under phase-transfer conditions," have been used to introduce the MPM group. The use of (n-Bu)4N I for the in situ preparation of the very reactive p-methoxybenzyl iodide often improves the protection of hindered alcohols." In the following example, selectivity is probably achieved because of the increased acidity of the 2 -hydroxyl group ... 

HBr, AcOH, reflux, 30 min, 85%. The efficiency of this method is significantly improved if a phase transfer catalyst ( -Ci6H33P Bu3 Br ) is added to the mixture. Methods that use HBr for ether cleavage can give bromides in the presence of benzylic alcohols. ... 

LY311727 is an indole acetic acid based selective inhibitor of human non-pancreatic secretory phospholipase A2 (hnpsPLA2) under development by Lilly as a potential treatment for sepsis. The synthesis of LY311727 involved a Nenitzescu indolization reaction as a key step. The Nenitzescu condensation of quinone 4 with the p-aminoacrylate 39 was carried out in CH3NO2 to provide the desired 5-hydroxylindole 40 in 83% yield. Protection of the 5-hydroxyl moiety in indole 40 was accomplished in H2O under phase transfer conditions in 80% yield. Lithium aluminum hydride mediated reduction of the ester functional group in 41 provided the alcohol 42 in 78% yield. 

Addition of the alcohol 42 to a solution of BF3 Et20/TMSCN in DCM provided the nitrile 43 in 83% yield. Hydrolysis of nitrile 43 then furnished amide 44 in 85% yield. Demethylation of the methoxyindole 44 with BBra in DCM provided the hydroxyindole 45 in 80% yield. This was followed by alkylation of 45 with the bromide 46 under phase transfer conditions to provide the phosphonate ester 47 and subsequent cleavage of the methyl ester by TMS-I furnished trimethylsilyl phosphonic acid 48, which upon alcoholic workup afforded LY311727. 

Alkenyl alcohols, (E) disubstituted, 55, 66 ALKYL HALIDES, alkenes from, 55, 103 C-ALKYLATION, phase transfer catalysis... 

The reaction between acyl halides and alcohols or phenols is the best general method for the preparation of carboxylic esters. It is believed to proceed by a 8 2 mechanism. As with 10-8, the mechanism can be S l or tetrahedral. Pyridine catalyzes the reaction by the nucleophilic catalysis route (see 10-9). The reaction is of wide scope, and many functional groups do not interfere. A base is frequently added to combine with the HX formed. When aqueous alkali is used, this is called the Schotten-Baumann procedure, but pyridine is also frequently used. Both R and R may be primary, secondary, or tertiary alkyl or aryl. Enolic esters can also be prepared by this method, though C-acylation competes in these cases. In difficult cases, especially with hindered acids or tertiary R, the alkoxide can be used instead of the alcohol. Activated alumina has also been used as a catalyst, for tertiary R. Thallium salts of phenols give very high yields of phenolic esters. Phase-transfer catalysis has been used for hindered phenols. Zinc has been used to couple... 

Transesterification has been carried out with phase-transfer catalysis, without an added solvent. In another procedure, RCOOR are converted to RCOOR" by treatment of the ester and an alcohol R OH with n-BuLi, which converts the R"OH to R"OLi. ... 

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

This reaction is similar to 13-1 and, like that one, generally requires activated substrates. With unactivated substrates, side reactions predominate, though aryl methyl ethers have been prepared from unactivated chlorides by treatment with MeO in HMPA. This reaction gives better yields than 13-1 and is used more often. A good solvent is liquid ammonia. The compound NaOMe reacted with o- and p-fluoronitrobenzenes 10 times faster in NH3 at — 70°C than in MeOH. Phase-transfer catalysis has also been used. The reaction of 4-iodotoluene and 3,4-dimethylphenol, in the presence of a copper catalyst and cesium carbonate, gave the diaryl ether (Ar—O—Ar ). Alcohols were coupled with aryl halides in the presence of palladium catalysts to give the Ar—O—R ether. Nickel catalysts have also been used. ... 

In 1988, Linstrumelle and Huynh used an all-palladium route to construct PAM 4 [21]. Reaction of 1,2-dibromobenzene with 2-methyl-3-butyn-2-ol in triethylamine at 60 °C afforded the monosubstituted product in 63 % yield along with 3% of the disubstituted material (Scheme 6). Alcohol 15 was then treated with aqueous sodium hydroxide and tetrakis(triphenylphosphine)palladium-copper(I) iodide catalysts under phase-transfer conditions, generating the terminal phenylacetylene in situ, which cyclotrimerized in 36% yield. Although there was no mention of the formation of higher cyclooligomers, it is likely that this reaction did produce these larger species, as is typically seen in Stephens-Castro coupling reactions [22]. 

Heteropoly acids can be synergistically combined with phase-transfer catalysis in the so-called Ishii-Venturello chemistry for oxidation reactions such as oxidation of alcohols, allyl alcohols, alkenes, alkynes, P-unsaturated acids, vic-diols, phenol, and amines with hydrogen peroxide (Mizuno et al., 1994). Recent examples include the epoxidations of alkyl undecylenates (Yadav and Satoskar, 1997) and. styrene (Yadav and Pujari, 2000). 

Alternatively, the Sn2 nucleophilic substitution reaction between alcohols (phenols) and organic halides under basic conditions is the classical Williamson ether synthesis. Recently, it was found that water-soluble calix[n]arenes (n = 4, 6, 8) containing trimethylammonium groups on the upper rim (e.g., calix[4]arene 5.2) were inverse phase-transfer catalysts for alkylation of alcohols and phenols with alkyl halides in aqueous NaOH solution to give the corresponding alkylated products in good-to-high yields.56... 

B. Potassium allyl- and crotyltrifluoroborates undergo addition to aldehydes in biphasic media as well as water to provide homoallylic alcohol in high yields (>94%) and excellent diastereoselectivity (dr >98 2). The presence of a phase-transfer catalyst (e.g., B114NI) significantly accelerates the rate of reaction, whereas adding fluoride ion retards the reaction (Eq. 8.70).165 The method was applied to the asymmetric total synthesis of the antiobesity agent tetrahydrolipstatin (orlistat).166... 

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