Of a- phenacyl

O-Alkylation of A-(phenacyl)- and Af-(pivaloylmethyl)-derivatives of A-(benzhydryl>-(2R,3R)-c(.v-2,3-epoxybutyramide gave 4,5,6,7-tetrahydro-4-aza-oxepin-5-ones by Sni reactions under basic conditions <00T3209>. 

It is also possible to protect the carbonyl moiety of a phenacyl bromide via the reaction with semicarbazide hydrochloride then the semicarbazone can be electrolyt-ically dimerized, ultimately to afford a 2,5-diarylfuran [86]. Alternatively, the elec-trolytically formed dimer can be converted... 

The absence of characteristic waves of the aldehydic group can, of course, be used as a proof of the absence of the group in a molecule. In this way, the absence of an aldehydic group has been proved (57) for absinthindiol, guajtriol C and artemazulene. The presence of a phenacyl group has been proved in the molecule of kynurenine (755). a,(3 unsatura-ted ketones can be distinguished from saturated ketones, e.g. A4-3-ketosteroids and A1 4-3-ketosteroids can be detected in the presence of 3-ketosteroids and can be even determined in a mixture (772). 

By protecting the carbonyl group of a phenacyl bromide through reaction with semicarbazide hydrochloride, by reducing the resultant semicarbazone at mercury in DMF containing lithium perchlorate to obtain a dimer, and by hydrolyzing the electro-lytically formed dimer, one can synthesize a variety of 2,5-diarylfurans in excellent yield [234], In addition, Barba and coworkers [235] demonstrated that reductive dimerization of the semicarbazone derivative of phenacyl bromide... 

Reduction of the semicarbazone of a phenacyl bromide in dimethylformamide (DMF) yields the bis-semicarbazone of 1,4-diaryl-1,4-butanedione, which in DMF forms 3,6-diarylpyridazine [4] or, after treatment with aqueous acid, 2,5-diary 1-furan [5], Reduction of phenacyl bromide in DMF is reported to give 2,4-diarylfuran [6]. 

Scheme 17.12 Attachment of a phenacyl group to a PS resin and subsequent use in peptide synthesis.

Another path of synthesis consists in condensing J -methyl-a-piperidol with benzoylacetic acid at pH 5. A 50% yield is thus obtained of a-phenacyl-AZ-methylpiperidine which is dehydrosedamine (91). 

Scheme 16.9. Modification and photolytic cleavage of a phenacyl ester-based linker.

To the best of our knowledge, the hrst paper which mentioned an A-(l-haloalkyl)pyridinium compound appeared 66 years ago in the Chemische Berichte (Krohnke 33CB1386). Tlie author described the reaction of phenacyl pyridinium derivatives 1 with bromine in acetic acid to give the halides 2 (36CB2006 37CB864). Tire addition of bromine to the double bonds of A-vinylpyridinium salts 3 and 4 giving the adducts 5 and 6 has also been reported (51CB399) (Scheme 1). 

With highly reactive alkyl halides, like allylic, benzylic or phenacyl halides, the ZjA-alkylation can be a serious side-reaction. Because of a SNl-like mechanism in those cases, the effect of enolate concentration on the reaction rate is low, and the resulting monoalkylester 5 may be more acidic than the unsubstituted starting material ... 

These workers used binary solvent systems over a range of mole fractions to determine, for each solute, the constants a and b of equation (8.2). For methyl and phenacyl esters, TLC was used, while overpressured layer chromatography (OPLC) was used for dansyl amino acids. Nurok and co-workers (11) also evaluated how the quality of a simulated separation varies with changing solvent strength by using the inverse distance function (IDF) or planar response function (PRF), as follows ... 

Heating phenacyl 2-aminobenzoate with phosphoryl chloride yields 2-phenyl-4,1-benz-oxazepin-5(17/)-one (1. R = H). The method has been applied to the synthesis of a number of analogs.423... 

A carboxylic acid (not the salt) can be the nucleophile if F is present. Mesylates are readily displaced, for example, by benzoic acid/CsF. Dihalides have been converted to diesters by this method. A COOH group can be conveniently protected by reaction of its ion with a phenacyl bromide (ArCOCH2Br). The resulting ester is easily cleaved when desired with zinc and acetic acid. Dialkyl carbonates can be prepared without phosgene (see 10-21) by phase-transfer catalyzed treatment of primary alkyl halides with dry KHCO3 and K2C03- ... 

The NMR spectrum of the phenacyl complex [PhCOCH2Co(CN)5] shows only a single resonance due to the methylene group, and it was... 

Phenacyl radicals can be generated from the corresponding xanthates and add in good yield to various substituted propenes. The products of the reaction can then be cyclized to tetralones using an equivalent of a peroxide.313... 

Phenacyl-3-phenyl-l,2-dihydroquinoxaline (208) gave 2-phenylquinoxaline (HC1, MeOH, H20, reflux, 15 min 53% acetophenone also isolated as its dinitrophenylhydrazone. Note that this is a passenger deacylation in the course of a dealkylation).782... 

The initial step in Scheme 91 presumably involves deprotonation of the phenacyl substituent to give a pyridinium ylide. Such ylides may be generated as reactive (unstable) intermediates in the synthesis of cycl[3.2.2]azines from iV-(trimethylsilylmethyl)-2-pyridones (Scheme 92) in the presence of an excess of DMAD, the cyclazine is the major product <2003S1398>. 

The course of the reaction of phenacyl bromides (39) with nickel carbonyl is markedly dependent on the solvent employed in tetrahydrofuran the products are 1,2-dibenzoylethanes (cf. 40) but in dimethylformamide, 2,5-diarylfurans (41) are obtained in moderate to excellent yield (Scheme 53).90 It is possible that the furan derivatives (41) arise via intermediate fi,y-epoxyketones which can be isolated as products from a number of a-bromo-ketone substrates [cf. 39 and Section II].28... 

Product distributions and reaction conversions of several different photochemical systems, irradiated by conventional UV source and by EDL in a MW-UV reactor (Fig. 14.5), were compared to elucidate the advantages and disadvantages of a micro-wave photochemical reactor [90], Some reactions, e.g. photolysis of phenacyl benzoate in the presence of triethylamine or photoreduction of acetophenone by 2-propa-nol, were moderately enhanced by MW heating. The efficiency of chlorobenzene photosubstitution in methanol, on the other hand, increased dramatically with increasing reaction temperature. 

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