Amide group 0-alkylation

Another variation of the Madelung synthesis involves use of an O-alkyl or O-silyl imidate as the C2 electrophile. The mechanistic advantage of this modification stems from avoiding competing N-deprotonation, which presumably reduces the electrophilicity of the amide group under the classical conditions. Examples of this approach to date appear to have been limited to reactants with a EW substituent at the o-alkyl group[15,16]. 

The amide group is readily hydrolyzed to acrylic acid, and this reaction is kinetically faster in base than in acid solutions (5,32,33). However, hydrolysis of N-alkyl derivatives proceeds at slower rates. The presence of an electron-with-drawing group on nitrogen not only facilitates hydrolysis but also affects the polymerization behavior of these derivatives (34,35). With concentrated sulfuric acid, acrylamide forms acrylamide sulfate salt, the intermediate of the former sulfuric acid process for producing acrylamide commercially. Further reaction of the salt with alcohols produces acrylate esters (5). In strongly alkaline anhydrous solutions a potassium salt can be formed by reaction with potassium / /-butoxide in tert-huty alcohol at room temperature (36). 

Apparently a substantial spacer is also allowable between I he aromatic ring and the carboxy group. Gemfibrozi 1 (52), a iiypotriglyceridemic agent which decreases the influx of steroid into the liver, is a cl ofibrate homologue. It is made readily liy lithium di isopropyl amide-promoted alkylation of sodium iso-propionate with alkyl bromide 51. 

Another approach to reduction of an amide group in the presence of other groups that are more easily reduced is to convert the amide to a more reactive species. One such method is conversion of the amide to an O-alkyl derivative with a positive charge on nitrogen.102 This method has proven successful for tertiary and secondary, but not primary, amides. 

For the primary and secondary a-alkoxy radicals 24 and 29, the rate constants for reaction with Bu3SnH are about an order of magnitude smaller than those for reactions of the tin hydride with alkyl radicals, whereas for the secondary a-ester radical 30 and a-amide radicals 28 and 31, the tin hydride reaction rate constants are similar to those of alkyl radicals. Because the reductions in C-H BDE due to alkoxy, ester, and amide groups are comparable, the exothermicities of the H-atom transfer reactions will be similar for these types of radicals and cannot be the major factor resulting in the difference in rates. Alternatively, some polarization in the transition states for the H-atom transfer reactions would explain the kinetic results. The electron-rich tin hydride reacts more rapidly with the electron-deficient a-ester and a-amide radicals than with the electron-rich a-alkoxy radicals. 

Examples of the so-called chaperon effect involving interaction between the electrophile and an appropriate substituent at the a-position in an alkyl chain prior to ring substitution at the ortAo-position have been explored in nitrations involving dilute solutions of nitric acid in dichloromethane. Aldehydic or ketonic carbonyl groups are most effective, but carboxyl, alkoxycarboxyl, and amide groups also work well. l-Phenylpropan-2-one, for example, forms 85% of l-(2-nitrophenyl)propan-2-one (5). 

The amide 504 may be made by ortholithiation of benzodioxolane 505, though a higher-yielding preparation starts from 1,2-dihydroxybenzoic acid 506. OrthoUthiation of 504, directed by the tertiary amide group, is straightforward, and gives the alkylated amide 503 (Scheme 196). 

Doxapram Doxapram, l-ethyl-4-(2-morpholinoethyl)-3,3-diphenyl-2-pyrrolidinone (8.2.4), is synthesized in the following manner. Diphenylacetonitrile in the presence of sodium amide is alkylated with l-ethyl-3-chlorpyrrolidine, giving (l-ethyl-3-pyrrolidinyl) diphenylacetonitrile (8.2.1). Acidic hydrolysis of the nitrile group gives (l-ethyl-3 pyrrolidinyl)diphenylacetic acid (8.2.2). Reacting this with phosphorous tribromide... 

Isopropamide Isopropamide, (3-carbamoyl-3,3-diphenylpropyl)di-tiO-propylmethyl ammonium iodide (14.1.25), is synthesized by alkylating diphenylacetonitrile with di-/io-propylaminoethylchloride in the presence of sodium amide, and the subsequent hydrolysis of the nitrile group of the resulting compound (14.1.23) to an amide group (14.1.24). Alkylation of this compound with methyliodide gives isopropamide (14.1.25) [19-22]. 

The trialkyloxonium salts are powerful alkylating agents. Trimethyl- and triethyloxonium tetrafluoroborates, in particular, have been widely employed for methylation and ethylation of sensitive or weakly nucleophilic functional groups. Alkylations of over 50 such functional groups have been reported in the literature. Examples include amides,4,7,13 16 lac-... 

Alkylations by oxonium salts have added several new weapons to the synthetic chemist s armamentarium. For example, the O-alkylated products from amides [R1C(OR)=NR2R3]+ (R == CH3 or C2H5) may be hydrolyzed under mild conditions to amines and esters,14-34 reduced to the amines RjCH-jNRaRa by sodium borohydride,13 converted to amide acetals RiC(OR)2NR2R3 by alkoxides,4-16 and (for R3 = H) deproton-ated to the imino esters R1C(OR)=NR2.16-18 Amide acetals and imino esters are themselves in turn useful synthetic intermediates. Indeed, oxonium salts transform the rather intractable amide group into a highly reactive and versatile functionality, a fact elegantly exploited in recent work on the synthesis of corrins.34... 

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