Gas-phase reactivity of charged pi-type biradicals

Four pi,pi-biradicals, 2,6-dimethylenepyridinium and the novel isomers N-(3-methylenephenyl)-3-methylenepyridinium, N-phenyl-3,5-dimethylenepyridinium, and N-(3,5-dimethylenephenyl)pyridinium ions, were generated and structurally characterized in a Fourier transform ion cyclotron resonance mass spectrometer. Their gas-phase reactivity toward various reagents was compared to that of the corresponding monoradicals, 2-methylenepyridinium, N-phenyl-3-methylenepyridinium, and N-(3-methylenephenyl)pyridinium ions. The biradicals reactivity was found to reflect their predicted multiplicity. The 2,6-dimethylenepyridinium ion, the only biradical in this study predicted to have a closed-shell singlet ground state, reacts significantly faster than the other biradicals, which are predicted to have triplet ground states. In fact, this biradical reacts at a higher rate than the analogous monoradical, which suggests that to avoid the costly uncoupling of its unpaired electrons, the biradical favors ionic mechanisms over barriered radical pathways. In contrast, the second-order reaction rate constants of the isomeric biradicals with triplet ground states are well approximated by those of the analogous monoradicals, although the final reaction products are sometimes different. This difference arises from rapid radical-radical recombination of the initial monoradical reaction products. The overall reactivity toward the hydrogen-atom donors benzeneselenol and tributylgermanium hydride is significantly greater for the radicals with the charged site in the same ring system as the radical site. This finding indicates that polar effects play an important role in controlling the reactivity of pi,pi-biradicals, just as has been demonstrated for sigma,sigma-biradicals.     

Theoretical and experimental investigations on the reactions of positively charged phenyl radicals with aromatic amino acids

The chemical behavior of positively charged phenyl radicals 3-dehydro-N-phenylpyridinium (a), N-(3-dehydro-5-chlorophenyl)pyridinium (b), and N-(3-dehydrophenyl)pyridinium (c) toward L-tyrosine, phenylalanine, and tryptophan was investigated in the gas phase both theoretically by performing molecular orbital calculations and experimentally by using FT/ICR mass spectrometry. All radicals react with phenylalanine and tryptophan nearly at the collision rate. The overall reactivity of the radicals toward tyrosine follows the order a > b > c, which is consistent with the electron affinity (EA) ordering of the radicals. The higher the electrophilicity (or EA) of the radical, the greater the reactivity. As expected, all radicals abstract a hydrogen atom from all of the amino acids. However, the most electrophilic radical a was also found to react with these amino acids via NH2 abstraction. A new reaction observed between radicals a-c and aromatic amino acids is the addition of the radical to the aromatic ring of the amino acid followed by Calpha-Cbeta bond cleavage, which leads to side-chain abstraction by the radical.     

A Fourier-transform ion cyclotron resonance study of the 3,5-didehydrophenyl cation

The 3,5-didehydrophenyl cation has been generated in good purity via sustained off-resonance irradiation for collision-activated dissociation of 3,5-dinitrobenzoyl chloride in a Fourier-transform ion cyclotron resonance mass spectrometer. Differences in the ion-molecule reactivity of this species from that of its cyclic and acyclic isomers allowed isomeric distinction to be achieved. This study represents the first definitive identification of this fundamentally interesting, doubly aromatic ion. However, the formation of the 3,5-didehydrophenyl cation was found to be the exception rather than the rule, with most 1,3,5-substituted benzenes yielding mainly acyclic C6H3+ isomers under electron ionization conditions. This mixed ion population was attributed to isomerization of fragmentation intermediates rather than any intrinsic instability of the 3,5-didehydrophenyl cation.     

Reactivity of a σ,σ,σ,σ-tetraradical: the 2,4,6-tridehydropyridine radical cation

The 2,4,6-tridehydropyridine radical cation, an analogue of the elusive 1,2,3,5-tetradehydrobenzene, was generated in the gas phase and its reactivity examined. Surprisingly, the tetraradical was found not to undergo radical reactions. This behavior is rationalized by resonance structures hindering fast radical reactions. This makes the cation highly electrophilic, and it rapidly reacts with many nucleophiles by quenching the N-C ortho-benzyne moiety, thereby generating a relatively unreactive meta-benzyne analogue.     

Reactivity of substituted charged phenyl radicals toward components of nucleic acids

Reactions of differently substituted phenyl radicals with components of nucleic acids have been investigated in the gas phase. A positively charged group located meta with respect to the radical site was employed to allow manipulation of the radicals in a Fourier-transform ion cyclotron resonance mass spectrometer. All of these electrophilic radicals react with sugars via exclusive hydrogen atom abstraction, with adenine and uracil almost exclusively via addition (likely at the C8 and C5 carbons, respectively), and with the nucleoside thymidine by hydrogen atom abstraction and addition at C5 in the base moiety (followed by elimination of (*)CH(3)). These findings parallel the reactivity of the phenyl radical with components of nucleic acids in solution, except that the selectivity for addition is different. Like HO(*), the electrophilic charged phenyl radicals appear to favor addition to the C5-end of the C5-C6 double bond of thymine and thymidine, whereas the phenyl radical preferentially adds to C6. The charged phenyl radicals do not predominantly add to thymine, as the neutral phenyl radical and HO(*), but mainly react by hydrogen atom abstraction from the methyl group (some addition to C5 in the base followed by loss of (*)CH(3) also occurs). Adenine appears to be the preferred target among the nucleobases, while uracil is the least favored. A systematic increase in the electrophilicity of the radicals by modification of the radicals' structures was found to facilitate all reactions, but the addition even more than hydrogen atom abstraction. Therefore, the least reactive radicals are most selective toward hydrogen atom abstraction, while the most reactive radicals also efficiently add to the base. Traditional enthalpy arguments do not rationalize the rate variations. Instead, the rates reflect the radicals' electron affinities used as a measure for their ability to polarize the transition state of each reaction.     

Reactivity and selectivity of charged phenyl radicals toward amino acids in a Fourier transform ion cyclotron resonance mass spectrometer

The reactivity of 10 charged phenyl radicals toward several amino acids was examined in the gas phase in a dual-cell Fourier transform ion cyclotron resonance mass spectrometer. All radicals abstract a hydrogen atom from the amino acids, as expected. The most electrophilic radicals (with the greatest calculated vertical electron affinities (EA) at the radical site) also react with these amino acids via NH(2) abstraction (a nonradical nucleophilic addition-elimination reaction). Both the radical (hydrogen atom abstraction) and nonradical (NH(2) abstraction) reaction efficiencies were found to increase with the electrophilicity (EA) of the radical. However, NH(2) abstraction is more strongly influenced by EA. In contrast to an earlier report, the ionization energies of the amino acids do not appear to play a general reactivity-controlling role. Studies using several partially deuterium-labeled amino acids revealed that abstraction of a hydrogen atom from the α-carbon is only preferred for glycine; for the other amino acids, a hydrogen atom is preferentially abstracted from the side chain. The electrophilicity of the radicals does not appear to have a major influence on the site from which the hydrogen atom is abstracted. Hence, the regioselectivity of hydrogen atom abstraction appears to be independent of the structure of the radical but dependent on the structure of the amino acid. Surprisingly, abstraction of two hydrogen atoms was observed for the N-(3-nitro-5-dehydrophenyl)pyridinium radical, indicating that substituents on the radical not only influence the EA of the radical but also can be involved in the reaction. In disagreement with an earlier report, proline was found to display several unprecedented reaction pathways that likely do not proceed via a radical mechanism but rather by a nucleophilic addition-elimination mechanism. Both NH(2) and (15)NH(2) groups were abstracted from lysine labeled with (15)N on the side chain, indicating that NH(2) abstraction occurs both from the amino terminus and from the side chain. Quantum chemical calculations were employed to obtain insights into some of the reaction mechanisms.     

Influence of hydrogen bonding on hydrogen-atom abstraction reactions of dehydropyridinium cations in the gas phase

The reactions of several substituted, positively charged dehydropyridinium cations with cyclohexane, methanol, and tetrahydrofuran have been examined in a Fourier-transform ion cyclotron resonance mass spectrometer. All of the charged monoradicals react with the neutral reagents exclusively via hydrogen atom abstraction. For cyclohexane, there is a good correlation between the reaction efficiencies and the calculated electron affinities at the radical sites; that is, the greater the electron affinity of the charged monoradical at the radical site, the faster the reaction. The reaction efficiencies with methanol and tetrahydrofuran, however, do not correlate with the calculated electron affinities. Density functional theory (DFT) calculations indicate that for these reagents a stabilizing hydrogen bonding interaction exists in the hydrogen atom abstraction transition states for some of the charged monoradicals but not for others. At both the MPW1K and G3MP2B3 levels of theory, there is a good correlation between the calculated activation enthalpies and the observed reaction efficiencies, although the G3MP2B3 method provides a slightly better correlation than the MPW1K method. The extent of enhancement in the reaction efficiencies caused by the hydrogen bonding interactions parallels the calculated hydrogen bond lengths in the transition states.     

Reactions of charged phenyl radicals with aliphatic amino acids in the gas phase

Gas-phase reactivity of five differently substituted positively charged phenyl radicals was examined toward six amino acids by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR). The reactivity of the radicals studied was determined by the electrophilicity of the radical, which can be characterized by the radical's electron affinity (EA). The larger the electron affinity of the radical, the higher the overall reaction rate. In addition to the expected H-atom abstraction, several unprecedented reaction pathways were observed, including NH2 abstraction, SH abstraction, and SCH3 abstraction. These reaction pathways dominate for the most electrophilic radicals, and they may not follow radical but rather nucleophilic addition-elimination mechanisms. Hydrogen abstraction from glycine was also investigated theoretically. The results indicate that hydrogen abstraction from alphaC of glycine is both kinetically and thermodynamically favored over the NH2 group. The ordering of transition state energies for hydrogen abstraction from the alphaC and NH2 groups was found to reflect the radicals' EA ordering.     

An electron-catalyzed cope cyclization. The structure of the 2,5-dicyano-1,5-hexadiene radical anion in the gas phase

The radical anion of 2,5-dicyano-1,5-hexadiene is shown to undergo Cope cyclization in a flowing afterglow-triple quadrupole apparatus. The cyclic structure of the 2,5-dicyano-1,5-hexadiene radical anion was established by using chemical reactivity. The ion reacts with CO2 and CS2 by addition, whereas the radical anions of closed-shell molecules such as fumaronitrile do not react with these reagents. The ion exhibits reactivity characteristic of a distonic ion in that it sequentially adds CO2 and NO or NO2. It reacts with NO by forming a product at m/z 135 corresponding to addition followed by loss of HCN. The reactivity and CID spectrum of the product ion at m/z 135 agrees with that of oximate ion, which requires a cyclic precursor ion. Attempts to generate radical anions of acrylonitrile and 2,6-dicyano-1,6-heptadiene were unsuccessful, providing additional evidence against a linear structure as a stable structure for 2,5-dicyano-1,5-hexadiene radical anion. The cyclization of the radical anion of the 2,5-dicyano-1,5-hexadiene is the first example of an electron-catalyzed Cope cyclization.     

3,5-Pyridyne--a heterocyclic meta-benzyne derivative

3,5-Pyridyne (3) has been generated by flash vacuum pyrolysis of 3,5-diiodopyridine (20) and 3,5-dinitropyridine (21) and characterized by IR spectroscopy in cryogenic argon matrices. The aryne can clearly be distinguished from other side products by its photolability at 254 nm, inducing a rapid ring-opening presumably to (Z)-1-aza-hex-3-ene-1,5-diyne. As byproducts of the pyrolysis, HCN and butadiyne were identified, together with traces of acetylene, cyanoacetylene, (E)-1-aza-hex-3-ene-1,5-diyne, and the 3-iodo-5-pyridyl radical (from 20). Several pathways for rearrangements and fragmentations of 3 and of the parent meta-benzyne (1) have been explored computationally by density functional theory and ab initio quantum chemical methods. The lowest energy decomposition pathway of biradicals 1 and 3 is a ring-opening process accompanied by hydrogen migration, leading to (Z)-hex-3-ene-1,5-diyne [(Z)-10] and (Z)-3-aza-hex-3-ene-1,5-diyne [(Z)-24], respectively. Both reactions require activation energies of 45-50 kcal mol(-1). Mechanisms leading from (Z)-24 or directly from 3 to the experimentally observed byproducts are discussed. Upon replacement of the C(5)H moiety by N in meta-benzyne, high-level calculations predict a modest shortening of the interradical distance by 5-7 pm and a reduction of the singlet-triplet energy splitting by 3 kcal mol(-1), in good agreement with isodesmic equations, according to which the singlet ground state of 3 is destabilized relative to 1 by 3-4 kcal mol(-1). In contrast to 3,5-borabenzyne (2), which is found to be doubly aromatic, nucleus-independent chemical shifts of 3 are almost identical to that of pyridine, indicating the absence of paramagnetic ring current effects that may be associated with "in-plane antiaromaticity". As compared with 1, the overall perturbation caused by the nitrogen atom in 3 is weak, and four electron, three center interaction is of minor importance in this molecule.     

Substituent effects on the nonradical reactivity of 4-dehydropyridinium cation

Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly differs from the reactivities of its isomers toward tetrahydrofuran. While only hydrogen atom abstraction was observed for the 2- and 3-dehydropyridinium cations, nonradical reactions were observed for the 4-isomer. In order to learn more about these reactions, the gas-phase reactivities of the 4-dehydropyridinium cation and several of its derivatives toward tetrahydrofuran were investigated in a Fourier transform ion electron resonance mass spectrometer. Both radical and nonradical reactions were observed for most of these positively charged radicals. The major parameter determining whether nonradical reactions occur was found to be the electron affinity of the radicals--only those with relatively high electron affinities underwent nonradical reactions. The reactivities of the monoradicals are also affected by hydrogen bonding and steric effects.     

Etude du caractere nucleophile des radicaux lors de la reaction de transfert sur la liaison O-O des peracides

Peracids RC0₃H yield free radicals R' which react either with the peracid or with solvent giving the alcohol ROH and the hydrocarbon RH. The nucleophilic character of the free radicals was modified either by substitution of the carbon bearing the odd electron by inductive groups or by changing the free radical hybridation by the means of blocked structures such as cyclic or bicyclic free radicals. For each R, the measurement of the ratio ROH/RH establishes a reactivity scale for R with the peracid O-O bond. This reactivity does not depend on free radical stability but depends strongly on nucleophilic character. A primary free radical is less reactive than a secondary one, and is much less reactive than a tertiary one. A bridgehead free radical as the bicyclo[2.2.1]heptyle-1 does not react with the peracid. These results are interpreted to indicate a transition state with charge transfer (polar effect), the peracid being electrophilic and the free radical nucleophilic; PMO theory is discussed.     

Addition of ester enolates to N-alkyl-2-fluoropyridinium salts: total synthesis of (+/-)-20-deoxycamptothecin and (+)-camptothecin

Several 4-substituted dihydropyridones or 2-pyridones have been prepared by nucleophilic addition of alpha-(methylsulfanyl)ester enolates to N-alkyl-2-fluoropyridinium salts, followed by acid hydrolysis or oxidation with concomitant hydrolysis, of the intermediate 2-fluoro-1,4-dihydropyridine adducts, respectively. Addition of the enolate derived from isopropyl alpha-(methylsulfanyl)butyrate to N-(quinolylmethyl)-2-fluoropyridinium triflate 21 followed by DDQ treatment gave pyridone 29, from which (+/-)-20-deoxycamptothecin (31), a known precursor of camptothecin, was synthesized by a radical cyclization-desulfurization, with subsequent elaboration of the lactone E ring by chemoselective reduction. A similar sequence starting from the enolate of a chiral 2-hydroxybutyric acid derivative (33) provides access to natural (+)-camptothecin (37).     

Alkylation of benzyl chloride by gaseous carbenium ions

The alkylation of benzyl chloride has been studied in the gas phase using radiolytically formed carbenium ions as the charged reagents. The intramolecular selectivity of the electrophilic attack, deduced from the composition of the neutral products, is characterized by the comparable reactivity of the aromatic ring and of the halogen atom of the substrate toward the gaseous cations. As to ring alkylation, the reactivity of the ortho positions of benzyl chloride is considerably lower than those of chlorobenzene. The results are compared with pertinent mass-spectrometric data, and discussed in connection with existing models of gas phase aromatic substitution by charged electrophiles.     

Anti-oxidant and pro-oxidant reactivities of copper(II), manganese(II) and iron(III) 3,5-di-<Emphasis Type="Italic">i</Emphasis>-propylsalicylate chelates during peroxidation of alkylbenzenes

Bioactive copper(II), iron(III), and manganese(II) 3,5-di-i-propylsalicylate (3,5-DIPS) chelates were investigated in order to determine their ability to inhibit the free radical initiated chain reactions leading to the peroxidation of isopropylbenzene (i-PrPh) and ethylbenzene (EtPh). Quantitative kinetic studies of these chelates established the following order of anti-oxidant reactivities: manganese(II)-(3,5-DIPS)₂>iron(III)(3,5-DIPS)₃>copper(II)₂(3,5-DIPS)₄> > 3,5-DIPS acid. The mechanism of anti-oxidant reactivity of these three chelates is established as being due, in part, to their chain-breaking capacity resulting from the chemical reduction of the generated peroxyl radical to yield alkybenzenelhydroperoxides via reaction of the 3,5-DIPS ligand with the peroxyl radical. In the case of manganese(II)3,5-di-i-propylsalicylate, the central metalloelement also interacts with the peroxyl radical. The manganese(II)-(3,5-DIPS)₂ and copper(II)₂(3,5-DIPS)₄ chelates were also found to exhibit alkylhydroperoxide pro-oxidative reactivity leading to the formation of the alkylbenzeneperoxyl radical. In addition, the manganese(II) atom underwent oxidation to manganese(III) with the formation of the alkylbenzenehydroperoxide or superoxide with air oxygen oxidation. Amyl acetate and dipropylamine (n-Pr₂NH) were added to the reaction mixture to model the biochemical presence of ester or amine cellular components. Addition of amyl acetate to the reaction mixture increased the anti-oxidant reactivity of manganese(II)-(3,5-DIPS)₂ while decreasing its pro-oxidant reactivity. The weaker anti-oxidant reactivites of iron(III)(3,5-DIPS)₃ and copper(II)₂(3,5-DIPS)₄ were less affected by the addition of amyl acetate and the pro-oxidant reactivity of copper(II)₂(3,5-DIPS)₄ was not changed by the addition of amyl acetate, while the pro-oxidant property of iron(III)(3,5-DIPS)₃ was eliminated. In contrast to 2,6-di-t-butyl-4-methylphenol, butylated hydroxy toluene (BHT), anti-oxidant reactivities of copper(II), iron(III), and manganese(II) 3,5-DIPS chelates were dramatically enhanced by the addition of n-Pr₂NH to the reaction mixture. It is concluded that all three metalloelement chelates react with and remove alkylbenzeneperoxyl radicals and the hydroperoxyl radical. The manganese(II)-(3,5-DIPS)₂ and copper(II)₂(3,5-DIPS)₄ chelates may also be useful in removing hydroperoxides in vivo. These reactivities, in addition to their established superoxide dismutase (SOD)-mimetic and catalase-mimetic reactivities, are suggested to possibly permit anti-oxidant and pro-oxidant reactivities in aqueous and organic cellular compartments.     

Gas phase ion chemistry of charged silver(I) adenine ions via multistage mass spectrometry experiments and DFT calculations

Electrospray ionization (ESI) of solutions containing adenine and AgNO(3) yields polymeric [Ad(x)+ Ag(y)-zH]((y-z)+) species. Density functional theory (DFT) calculations have been used to examine potential structures for several of the smaller ions while multistage mass spectrometry experiments have been used to probe their unimolecular reactivity (via collision-induced dissociation (CID)) and bimolecular reactivity (via ion-molecule reactions with the neutral reagents acetonitrile, methanol, butylamine and pyridine). DFT calculations of neutral adenine tautomers and their silver ion adducts provide insights into the binding modes of adenine. We find that the most stable [Ad + Ag](+) ion does not correspond to the most stable neutral adenine tautomer, consistent with previous studies that have shown that transition metal ions can stabilize rare tautomeric forms of nucleobases. Both the charge and the stoichiometry of the [Ad(x)+ Ag(y)-zH]((y-z)+) complexes play pivotal roles in directing the types of fragmentation and ion-molecule reactions observed. Thus, [Ad(2)+ Ag(2)](2+) is observed to dissociate to [Ad + Ag](+) and to react with butylamine via proton transfer, while [Ad(2)+ Ag(2)- H](+) fragments via loss of neutral adenine to form the [Ad + Ag(2)- H](+) ion and does not undergo proton transfer to butylamine. DFT calculations on several isomeric [Ad(2)+ Ag(2)](2+) ions suggest that planar centrosymmetric cations, in which two adjacent silver atoms are bridged by two N7H adenine tautomers via N(3),N(9)-bidentate interactions, are the most stable. The [Ad + Ag(2)-H](+) ion adds two neutral reagents in ion-molecule reactions, consistent with the presence of two vacant coordination sites. It undergoes a silver atom loss to form the [Ad + Ag - H](+) radical cation, which in turn fragments quite differently to the even electron [Ad + Ag](+) ion. Several other pairs of radical cation/even electron adenine-silver complexes were also found to undergo different fragmentation reactions.     

Promotion of Sandmeyer hydroxylation (homolytic hydroxydediazoniation) and hydrodediazoniation by chelation of the copper catalyst: bidentate ligands

Relative to the rate observed for the hexa-aqua ion, Cu(OH(2))(6)(2+), chelation of the copper catalyst by certain bidentate ligands enhances the rate of hydroxydediazoniation reaction (Sandmeyer hydroxylation); the ligands also provide a source of hydrogen in competitive hydrodediazoniation (H-transfer) reactions. By using the cyclisation of 2-benzoylphenyl radical as a radical clock, it has been possible to evaluate absolute rate constants for both processes effected by a variety of complexes involving one or two bidentate ligands (2-aminocarboxylate, 2-hydroxycarboxylate, 1,3-dicarboxylate, 1,2-diamine). The radical exhibits electrophilic character in both processes. The pattern of behaviour observed suggests the rate determining step in hydroxylation is reaction of the aryl radical at the metal centre to form an organocopper adduct which is rapidly converted into products. The relative reactivities of different complexes are explained qualitatively in terms of variations in the ligand field and Jahn-Teller distortion splittings of the copper d orbitals. Hydrodediazoniation is an S(H)2 H-abstraction process. Generally, coordination by Cu(2+) deactivates the first added ligand relative to its reactivity as a free species in the same state of protonation. For the majority of complexes studied, the relative reactivity as H-donors of 1 : 1 and 1 : 2 complexes is statistically determined but an additional electronic effect is discerned for doubly charged ions.     

Alternative reagents for chemical noise reduction in liquid chromatography-mass spectrometry using selective ion-molecule reactions

Reduction of ionic chemical background noise based on selective gas-phase reactions with chosen neutral reagents has been proven to be a very promising approach in liquid chromatography—mass spectrometry (LC-MS). In this study further investigations on alternative reagents including the disulfides (dimethyl disulfide, diethyl disulfide, methyl propyl disulfide), dimethyl trisulfide, ethylene oxide, and butadiene monoxide, for example, have been carried out. Tandem mass spectrometric studies of ion/molecule reactions indicate that—besides dimethyl disulfide—ethylene oxide and butadiene monoxide also exhibit very efficient reactions with background ions. Furthermore, it is confirmed that the reactions are very selective according to the test with some analyte ions. In contrast to its rapid reactions with background ions, ethylene oxide does not react, or reacts much less, with these analytes. Therefore, it can be used as an alternative reagent for noise reduction. Although reactions of the other tested neutral reagents with background ions are evaluated, they are generally not suitable as reagents for this purpose because of lack of reactivity or dramatic ion losses during reactions.     

Reaction of asymmetric organomercury compounds with thallium trichloride

Summary Thallium trichloride exchanges two of its halogen atoms only for a radical that possesses a trans-configuratlon in cis-trans compounds, or for a radical that experiences electrophilic attack by the hydrogen ion in the decomposition of RHgR' by hydrochloric acid.     

Syntheses of some novel imidazolidinethiones and condensed imidazoles containing arylazo moieties starting from cyanothioformamides

Cyclocondensation of cyanothioformamides ( 1 ) with arylhydrazonomalononitriles ( 2 ) afforded the novel imidazole derivatives ( 4a–e ) in good yields. Isothiocyanatoazobenzene ( 6 ) was allowed to react with potassium cyanide and gave the new cyanothioformamide ( 7 ) which was reacted with 4‐chlorophenyl isocyanate to yield imidazolidinethione ( 8 ). Compound ( 8 ) was subjected to react with hydrochloric acid, o‐phenylenediamine, 4‐methylaniline, and hydrogen sulfide and furnished compounds ( 10 ), ( 11 ), ( 12 ), and ( 15 ), respectively. Also, the reactivity of thiohydantoin ( 15 ) toward some electrophilic reagents such as N,N‐dimethylformamide‐dimethylacetal and arylidene‐malononitriles was investigated. The structure of the synthesized compounds was established by analytical and spectral data. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:218–225, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20113