Synthesis of imidazolyl dithiocarbamates and their reactions with phenacyl bromides

The reactions of ethyl (5-carbamoyl-3H-imidazol-4-yl)dithiocarbamate with phenacyl bromides afford the S-alkylation products as a mixture of E/Z-isomers, which undergo cyclization to 5-(2-oxo-4-arylthiazol-3-yl)-1H-imidazole-4-carboxamides under the action of a base.     

Regioselective alkylation of isopropylidene- and cyclohexylidenepropanedinitrile with phenacyl bromides

Alkylation of isopropylidene- and cyclohexylidenepropanedinitrile with phenacyl bromides gave 2,2-bis(2-aryl-2-oxoethyl)propanedinitriles. Direct alkylation of propanedinitrile with phenacyl bromides afforded only 2-(2-aryl-2-oxoethyl)propanedinitriles.     

Formation of homoallylic bromohydrins in indium-mediated allylation reactions of phenacyl bromides in aqueous solution

A method is described for carrying out indium-mediated allylation reactions of phenacyl bromides in aqueous solution that form homoallylic bromohydrins. By employing subsequent base treatment, the homoallylic bromohydrins were converted to allylic epoxides. Finally, the process has been used as a key step in a concise sequence for the synthesis of 3-allylbenzofuran.     

Unusual product from the acid-catalyzed one-pot,multicomponent reaction of thiocarbohydrazide,aldehydes, and phenacyl bromides

A one-pot, three-component protocol for the synthesis of novel five-membered thiazole ring bonded to two hydrazone motifs is described. The acid-catalyzed reaction of one equivalent of thiocarbohydrazide, two equivalents of aromatic aldehydes, and one equivalent of phenacyl bromides afforded the five-membered thiazole ring. The reactions proceed with novel chemoselectivity. Similar reported protocols have always afforded 1,3,4-thiadiazines.     

Diminished reactivity of ortho-substituted phenacyl bromides toward nucleophilic displacement

A systematic increase of substitution rates by tert-butylamine on alpha-bromopropiophenones is observed with meta or para substituents with increasing electron-withdrawing ability (k x 10(3) L M(-1) min(-1) = 12.7 (p-CH(3)), 15.7 (o-F), 20.5 (H), 20.0 (p-Cl), 23.6 (m-Cl), 27.3 (p-CF(3))). Within an ortho-substituted series, the reactivities decrease (k x 10(3) L M(-1) min(-1) = 7.64 (o-OCH(3)), 5.31 (o-CH(3)), 2.85 (o-Cl), 2.40 ( o-CF(3))). Ortho-substitution results occur from rotational barrier effects and an Adelta(sigma)+ Bdelta(sigma)+ repulsion. The major bonding contribution between reaction and alpha-substituent centers (A-B) is only the sigma bond. When pi bonding is allowed between A and B (meta/para-substitution), delocalization and stabilization of the reacting center occurs.     

Reaction of 3-hetero-substituted 2-phenyl-4-thioxo-3,4-dihydro-quinazolines with acyl chlorides and phenacyl bromides

Some 2, 5-disubstituted 1, 3, 4-thiadiazoles 5 were obtained by reaction of 3-amino-2-phenyl-4-thioxo-3, 4-dihydroquinazoline ( 1 ) with acyl chlorides. Reaction of 3-hydroxy-2-phenyl-3, 4-dihydroquinazoline ( 3 ) with phenacyl bromides was carried out either in dry acetonitrile or dimethylformamide to give 2-phenyl-4-phenacylthio-3-quinazolinium N-oxides 7 or 2-phenyl-4-phenacylidene-1H-3-quinazolinium N-oxides' 8 , respectively.     

Carbon-13 NMR spectra of some 4-substituted phenacyl bromides

The ¹³C NMR signals for some 4- substituted phenacyl bromides were assigned. The experimental chemical shifts of the aromatic ring carbons are in close agreement with those calculated using substituent chemical shifts. Both the carbonyl and the α-methylene carbons exhibit upfield shifts compared with those of the corresponding 4-substituted acetophenones.     

Kinetics and mechanism of the pyridinolysis of phenacyl bromides in acetonitrile

Kinetic studies of the reactions of substituted phenacyl bromides (YC6H4COCH2Br) with pyridines (XC5H4N) are carried out in acetonitrile at 45.0 degrees C. A biphasic Bronsted plot is obtained with a change in slope from a large (betaX approximately equals 0.65-0.80) to a small (betaX approximately 0.36-0.40) value at pKa = 3.2-3.6, which can be attributed to a change in the rate-determining step from breakdown to formation of a tetrahedral intermediate in the reaction path as the basicity of the pyridine nucleophile increases. This mechanism is supported by the faster rates with pyridines than with anilines and the change of cross-interaction constant rhoXY from a large positive (rhoXY = +1.4) to a small positive (rhoXY approximately +0.1) value. The large magnitude of Hammett rhoX (= -5.5 to -6.9) values for the pyridines with electron-withdrawing substituents and positive deviations of the pi-acceptors, p-CH3CO and p-CN, are quite similar to those for the pyridinium ion formation equilibria. The activation parameters are also in line with the proposed mechanism.     

Debromination of phenacyl and benzylic bromides with tertiary stibine and the mechanistic consideration

Tributylstibine is an efficient reagent for debromination of phenacyl and arylmethyl bromides. The mechanistic difference between stibine and phosphine is discussed briefly.     

Reactions of ortho oxy-substituted benzyl and phenacyl bromides in dimethyl sulphoxide

o-Acetoxy- and o-benzoyloxy-benzyl bromides and tosylates oxidatively rearrange in moist dimethyl sulphoxide to o-hydroxybenzyl esters; o-acetoxy- and o-benzoyloxy- phenacyl bromides rearrange to mixtures of 2-hydroxycoumaran-3-ones and o-hydroxyphenacyl esters; o-hydroxyphenacyl bromides also yield 2-hydroxycoumaran-3-ones, together with o-hydroxyphenacyl alcohols. 2-Acetoxybenzaldehyde is reductively rearranged by sodium borohydride to o-hydroxybenzyl acetate.     

Reactions of substituted phenacyl bromides with various bases. o- and p-nitrophenacyl bromide. I

The products obtained from the reaction of o- and p-nitrophenacyl bromide with various bases is described.     

Reactions of substituted phenacyl bromides with various bases: p-methyl- and p-methoxyphenacyl bromide. II

The products obtained from the reaction of p-methyl- and p-methoxyphenacyl bromide with various bases are described.     

Synthesis and properties of 1,3,4-thiadiazine derivatives. 1. Investigation of the condensation of substituted phenacyl bromides and bromoacetylpyridines with thiosemicarbazide

2-Amino-5-aryl(pyridyl)-6H-1,3,4-thiadiazines ana isomeric 2-hydrazino-4-aryl(pyridyl)thiazoles, the ratio of which depends on the reaction conditions, were obtained by the reaction of substituted phenacyl bromides and bromoacetylpyridines with thiosemicarbazide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 843–846, June, 1991.     

Thiophene-2-carbaldehyde and benzaldehyde thiosemicarbazones in reactions with propargyl bromide and 1,3-dibromopropyne

The reaction of thiophene-2-carbaldehyde and benzaldehyde thiosemicarbazones with propargylbromide in methanol provided S-(2-propyne)thiosemicarbazones hydrobromides of thiophene-2-carbaldehyde and benzaldehyde. Reaction products obtained from thiosemicarbazones and 1,3-dibromopropyne in methanol at heating were 2-thenilydene(benzylidene)azino-4-bromomethylidene-4,5-dihydrothiazol-3-ium bromides.     

Electrochemical dimerization of phenacyl bromides N-acylhydrazones—a new way to 1-N-acylamino-2,5-diaryl-pyrroles

Cathodic reduction of phenacyl bromides N-acyl hydrazones lead to dimeric 1,4-diaryl-1,4-butanedione di-N-acylhydrazones, which give the corresponding 1-N-acylamino-2,5-diarylpyrroles in good yields.     

Mechanisms of elimination reactions—XXVII: The reactions of 1-arylethyldimethylsulfonium bromides with sodium ethoxide in ethanol

Treatment of 1-phenylethyldimethylsulfonium bromide 1 with sodium ethoxide in ethanol at 35° affords four products by five reaction paths: styrene 2 by E2 and α'-β mechanisms, ethyl 1-phenylethyl ether 3 and methyl 1-phenylethyl sulfide 4 by the S_N2 mechanism, and methyl o-ethylbenzyl sulfide 5 by a Sommelet-Hauser rearrangement. Isotope effects of 5.9 and 3.5 for E2 and α'-β reactions were estimated by comparing the deuterium content of methyl sulfide from β-d₃, and α-d₇ (all α-positions exchanged) sulfonium salt. Product analyses on products from the unsubstituted, p-methyl, p-fluoro, p-bromo and m-chloro sulfonium salts were combined with overall rates to calculate partial rates for the formation of each product. These partial rates were fitted to the Hammett equation to give values for each product as follows: 2, 0.95±0.19; 3, ?0.63±0.41; 4, 0.95±0.11; 5, 4.84±0.38. The mechanistic implications of the results are discussed.     

Synthesis and reactions of N-Aryl-C-arylsulfonylformohydrazidoyl bromides

Bromination of 1-arylsulfonyl-1,2-propanedione-1-aryl-hydrazones 7 in a mixture of acetic acid and acetic anhydride in the presence of sodium acetate gave N-aryl-C-arylsulfonylformohydrazidoyl bromides 5. Treatment of 5 with dibenzoylmethane, acetylacetone, ethyl acetoacetate and ethyl benzoylacetate in ethanol in the presence of sodium ethoxide yielded the pyrazole derivatives 8-11 , respectively. Reaction of 5 with potassium thiocyanate afforded the thiadiazoline derivative 14. The bromides 5 also react with nucleophiles such as morpholine, piperidine, phenoxide, thiophenoxide and benzenesulfinate anions to give the corresponding substitution products 19-23 , respectively. The structures of the products 8-23 were assigned and confirmed on the basis of their spectral and elemental analyses, their chemical behaviour and alternate synthesis wherever possible.     

Reactions of benzimidazole-2-carbaldehyde with enamines

Benzimidazole-2-carbaldehyde reacts with 1-morpholinocyclohexene, 1-morpholinocyclopentene, and aminocrotonic ester upon heating to form 4a,11-dimorpholino-1,2,3,4,11,11a-hexahydro-4aH-indolo[1,2-a]benzimidazole, 2-(2-morpholino-4,5-dihydrofulvenyl)benzimidazole, and 4-(benzimidazol-2-yl)-3,5-diethoxycarbonyl-2,6-dimethyl-1,4-dihydropyridine, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 566–571, March, 1999.     

Synthesis and modification of 1-vinylpyrrole-2-carbaldehyde polymers

1-Vinylpyrrole-2-carbaldehydes, viz., 5-phenyl-1-vinylpyrrole-2-carbaldehyde, 5-(2-thienyl)-1-vinylpyrrole-2-carbaldehyde, 1-vinyl-4,5,6,7-tetrahydroindole-2-carbaldehyde, and 1-vinyl-4,5-dihydrobenz[g]indole-2-carbaldehyde, are polymerized in the presence of 2,2-azobisisobutyronitrile to form soluble paramagnetic oligomers. A possibility of oligomer modification through the aldehyde moiety with amines and thiols was shown. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2134–2137, November, 2007.     

Coupling reactions of aryl bromides with 1-alkynols catalysed by a tetraphosphine/palladium catalyst

cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C₃H₅)]₂ system catalyses efficiently the coupling reactions of aryl halides with a variety of alkynols such as propargyl alcohol, but-1-yn-4-ol, pent-1-yn-5-ol or hex-1-yn-6-ol. The catalyst can be used at low loading. Higher reaction rates were observed in the presence of but-1-yn-4-ol, pent-1-yn-5-ol or hex-1-yn-6-ol than with propargyl alcohol. The protection of the alcohol functions as an ether or a silyloxy group led generally to similar or better results than the reactions performed with the unprotected alcohols.