Phase transfer catalysis benzyltriethylammonium

In contrast, liquidiliquid phase-transfer catalysis is virtually ineffective for the conversion of a-bromoacetamides into aziridones (a-lactams). Maximum yields of only 17-23% have been reported [31, 32], using tetra-n-butylammonium hydrogen sulphate or benzyltriethylammonium bromide over a reaction time of 4-6 days. It is significant that a solidiliquid two-phase system, using solid potassium hydroxide in the presence of 18-crown-6 produces the aziridones in 50-94% yield [33], but there are no reports of the corresponding quaternary ammonium ion catalysed reaction. Under the liquidiliquid two-phase conditions, the major product of the reaction is the piperazine-2,5-dione, resulting from dimerization of the bromoacetamide [34, 38]. However, only moderate yields are isolated and a polymer-supported catalyst appears to provide the best results [34, 38], Significant side reactions result from nucleophilic displacement by the aqueous base to produce hydroxyamides and ethers. 

Undoubtedly the most important and widely used procedure for the generation of dichlorocarbene involves the reaction of chloroform with aqueous sodium hydroxide under the conditions of phase transfer catalysis (PTC), introduced by Makosza.20-22 Under these conditions chloroform reacts with sodium hydroxide to form sodium trichloromethylide which on exchange with a quaternary ammonium salt, usually benzyltriethylammonium chloride, is converted to the unstable quaternary ammonium methylide which dissociates in the organic phase to give dichlorocarbene. The dichlorocarbene irreversibly adds to the alkene (Scheme 1). 

Phase transfer catalysis was found <90CCC597> to be successful for /V-substitution of the furo[3,2-6]pyrrole system. The reaction of furo[3,2-fe]pyrroles with lithium hydride in DMF furnished N-lithium derivatives, which gave jV-acetyl derivatives with acetyl chloride. The same compounds can be obtained by boiling in acetic anhydride. The treatment of furo[3,2-fe]pyrrole derivatives with acrylonitrile in pyridine in the presence of benzyltriethylammonium hydroxide gave 4-(2-cyano-ethyl)furo[3,2-6]pyrrole derivatives. Phase transfer catalysis has been employed for the preparation of variously substituted 4-phenylsulfonylfuro[3,2-ft]pyrroles and l-phenylsulfonylbenzo[fe]furo [3,2-/>]pyrroles <94CCC499>. 

The synthesis of 1,1-diiodocyclopropane is carried out via addition of diiodocarbene (car-benoid) to alkenes the carbene, in turn, is generated from iodoform and a base. The process is realized using phase-transfer catalysis,(33% or 50%aqueous sodium hydroxide and a quaternary ammonium salt, typically benzyltriethylammonium chloride, as a catalyst) or in the presence of potassium ter/-butoxide in /ert-butyl alcohol 25,127,128 g... 

A potentially useful variation of the standard elimination procedure is the use of phase-transfer catalysis. Thus, ethyl 2,2-dimethyl-3-methylenecyclopropanecarboxylate (23) was obtained in 76% yield by reaction of the corresponding bromo ester 22 with 50% aqueous sodium hydroxide and a catalytic amount of benzyltriethylammonium chloride. This procedure is superior to other elimination methods (see also Section 5.2.2.1.1.2.). ... 

SoHd-liguid phase-transfer catalysis. Crown ethers have commonly been used as catalysts for reactions between a solid-liquid interface, and quaternary ammonium and phosphonium salts have been used only as catalysts for reactions in two-phase liquid liquid reactions. However, several laboratories have reported that the latter catalysts are also satisfactory for two-phase solid liquid reactions. Thus dichlorocarbene can be generated from chloroform and solid sodium hydroxide under catalysis from benzyltriethylammonium chloride in yields comparable to those of the classical Makosza method. Another example of this type of catalysis is the oxidation of terminal and internal alkynes by solid potassium permanganate in CH2CI2 with Adogen 464 as catalyst. Aliquat 336 has been found to be as satisfactory as a crown ether for certain displacement reactions with NaOAc, KSCN, KNOa, and KF in CH3CN or CHaCla. ... 

Sodium hydroxide I benzyltriethylammonium chloride 5-Chloropyrazoles from (a-azoalkylidene)phosphoranes Phase transfer catalysis... 

An important industrial reaction and one of the earliest applications of phase transfer catalysis by quaternary ammonium salts is the synthesis of polycarbonates [13]. Typically, 2,2-(4,4 -dihydroxydiphenyl)propane(bisphenol A) is dissolved in concentrated aqueous sodium hydroxide and exposed to a dichloromethane solution of phosgene. Salts such as benzyltriethylammonium chloride or tertiary amines catalyze the condensation polymerization [13—18]. The two phase polymerization is formulated in equation 6.6. 

Phase transfer catalysis has been utilized in the orrto-metallation of thiobenzo-phenone derivatives. Triiron dodecacarbonyl reacts with thiones in benzene solution in the presence of benzyltriethylammonium chloride and aqueous sodium hydroxide to give the complex shown in equation 9.17. Thiobenzophenone, 4,4 -dimethylthio-benzophenone, 4,4 -dimethoxythiobenzophenone and thio-Micheler ketone were all successfully metallated in 70%, 36%, 80% and 76% yields respectively. 

Phase transfer catalysis. A 33%-aq. soln. of NaOH added to an ice-cooled vigorously stirred soln. of skatole and benzyltriethylammonium chloride in chloroform, stirring and ice-cooling continued 6 hrs., then stirred 24 hrs. at room temp. 

Phase-transfer catalysis has also been successfully employed to achieve epoxidation. A variety of cyclic rran5-substituted diols in dichloromethane were treated with a 50% aqueous solution of sodium hydroxide in the presence of the phase-transfer catalyst benzyltriethylammonium bromide. Consistently good yields were achieved for these as well as glycosidic and acyclic substrates (eq 17). ... 

It is important to note that even certain phase-transfer catalysts can be carbonylated to carboxylic acids, not by cobalt tetracarbonyl anion catalysis, but by acetylcobalt tetracarbonyl. This is a slow but high-yield reaction that occurs for quaternary ammonium salts that are capable of forming reasonably stable free radicals. For example, phenylacetic acid is formed in 95% yield from benzyltriethylammonium chloride (benzyl radi-... 

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