Electronic effects of conjugated enones on their reactivity in transformations of ADDN type

Using RHF/3-21G, RHF/6-31G(d, p), MP2/6-31G(d, p), B3LYP/6-31G(fd, p) approximations the structure and ¹³C NMR spectra of 2-alkylsubstituted cyclohexene-2-ones and 2-alkylacroleins are studied and calculated. In the series of 2-alkylcyclohexene-2-ones the effect of the substituent on a deviation from coplanarity of the C=C-C=O fragment is more expressed in comparison with 2-alkylacroleins. This deviation (5°) is not enough to explain the observed properties of 2-alkylcyclohexene-2-ones due to disturbed conjugation. The particular behavior of (R)-4-mentenone in reactions of 1,4-addition and ozonolysis is explained by a more expressed +I-effect of the alkyl substituent in α-position.     

Potentiometric study on acid properties of some 4-hydroxy-6H-1,3-oxazin-6-ones. Structure-biological activity relationship

4-Hydroxy-6H-1,3oxazin-6-ones exhibit properties of weak OH acids. These compounds are readily methylated with diazomethane to give the corresponding 4-methoxy derivatives. According to the potentiometric titration data, the pK _a values of 2-methoxy-and 2-methylsulfanyl-substituted 4-hydroxy-6H-1,3-oxazin-6-ones range from 7.45 to 8.42, depending on the substituent in position 5 of the heteroring. 4-Hydroxy-6H-1,3-oxazin-6-ones in biological media exist mainly in the neutral form.     

Reaction of catalytic enantioselective reductive aminolysis of δ2-oxazolin-5-ones as a method of asymmetric synthesis of α-amino acids

This investigation is devoted to the interaction of Δ²-oxazolin-5-ones, S(—)-α-phenylethy lamine and H₂ in the presence of PdCl₂ which yields α-phenylethylamides of acylamino acids of the S,S configuration, hydrolysis of the latter compounds resulting in the formation of optically pure amino acids and providing for chiral amine recycling. In DME, double bond saturation and ring opening in Δ²-oxazolin-5-one occur within the catalytic complex sphere without the intermediate formation of saturated oxazolinones or unsaturated amides. In t-BuOH, saturated oxazolinones are formed as intermediates. The catalyst formed in situ was shown to be a zero-valent Pd complex with S(—)-α-phenylethylamine stabilized by substrate coordination. The stereochemical pathway of the reactions has been traced. Reductive aminolysis involves cis-addition of H₂, while in reductive methanolysis H₂ trarns-addition occurs. The suggested process mechanism accounts for the ratio of aminolysis and racemization rates for saturated oxazolinones and the ratio of diastereomers of α-phenylethylamides of acylamino acids obtained by reacting unsaturated Δ²oxazolin-5-ones with S(—)-α-phenyl-ethylamine. In agreement with the postulated mechanism, the catalyst enantioselectivity is observed at the steps of substrate addition to the catalyst and proton transfer to the α-C-center, provided the process is carried out in DME. In the case of t-BuOH, the enantiodifferentiating action of the catalyst vanishes as a result of racemization, and process stereo selectivity appears at the step of saturated oxazolinone aminolysis with a chiral amine.     

Synthesis and properties of quinazoline derivatives containing cymantrenyl group

The synthesis of new quinazoline derivatives with 2,3- and 4-positioned cymantrenyl fragment is described. Alkylation of 2-substituted quinazolin-4-ones with cymantrenylalkyl bromides on using K₂CO₃, potassium tert-butoxide, and sodium hydride as bases has been studied. It is established for the first time that condensation of 2-methylquinazolin-4-ones with aldehydes can cause elimination of the substituent at the nitrogen atom in position 3. The new cymantrene derivatives possess fluorescence properties.     

Selectfluor-mediated mild oxidative halogenation and thiocyanation of 1-aryl-allenes with TMSX (X = Cl,Br, I,NCS) and NH4SCN

Presence of TMSX (X = Cl, Br, I) unleashes the oxidative character of Selectfluor and provides a mild dihalogenation method for 1-arylallenes. Preference for 2,3-addition was observed with TMSCl in MeCN irrespective of the nature of the substituent on the aryl moiety, whereas 1,2-addition was preferred in [BMIM][BF₄]. With TMSBr and TMSI only products corresponding to 2,3-addition were observed. Reactions carried out with TMSBr in IL solvents gave the corresponding monobromoalkenes as a major product along with the isomeric dibromo-alkenes. Reaction with NH₄SCN provided convenient access to dithiocyanate derivatives. The same products were formed via TMS-NCS/Selectfluor. Formation of common products via TMSNCS and NH₄SCN points to the formation and interplay of SCN⁺/NCS⁺ as incipient electrophiles.     

Synthesis and coordinating properties of 5-phenyl- and 5-pyridylmethylidene-substituted 2-selenohydantoines and 2-selenoimidazol-4-ones

2-Selenoimidazolidin-4-ones and 2-selenoimidazol-4-ones containing phenylor pyridylmethylidene substituent at position 5 were synthesized. The structure of 3-benzyl-2-selenohydantoine was confirmed by X-ray crystallography. A series of 2-(methylseleno)imidazol-4-ones was obtained by alkylation of 3,5-disubstituted selenohydantoines with methyl iodide. The synthesized selenohydantoines and 3-benzyl-5-pyridylmethylidene-2-(methylseleno)imidazol-4-ones were examined in the complexation reactions with CoCl₂, NiCl₂, CuCl₂, and Cu^I(CH₃CN)₄ClO₄; electrochemical investigations showed that reduced forms of the copper-containing complexes were stable     

Nucleophilic additions on acetyldioxanes derived from (−)-(1R)-myrtenal used as chiral auxiliaries: substituent effects on the stereochemical outcome

The synthesis of acetyldioxanes 4 and 9a starting from (?)-(1R)-myrtenal is described. The products were treated with a representative series of nucleophilic reagents (RMgX, RLi, NaBH₄ and LiAlH₄) to assess the effect of the substituent at C-3 on the stereochemical outcome. It was observed that the nucleophiles preferred the re-face of the CO group when the equatorial substituent at C-3 was a methyl group, whereas a phenyl group at the same position induced the addition through the si-face, thus allowing access to either desired stereochemistry of a final product. This behavior suggests that the formation of the expected Cram-chelated coordination complex takes a coplanar orientation with the C-3 equatorial substituent. Moreover, Grignard reagents were the most stereoselective nucleophiles. The stereochemistry of the addition was established by X-ray diffraction and chemical correlation.     

Reaction of N-acetyl- and N-[1-(arylsulfonylimino)ethyl]-1,4-benzoquinone imines with sodium arenesulfinates

N-Acetyl- and N-[1-(arylsulfonylimino)ethyl]-1,4-benzoquinone imines having no substituent in the 2- and/or 6-position of the quinoid ring react with sodium arenesulfinates preferentially according to the 1,4-addition pattern. The presence of an ArSO₂N group favors radical ion reaction with formation of 1,6-addition products.     

Reactions of 4-acyl-1-alkoxyaryl-5-aryl-3-hydroxy-2,5-dihydro-1H-pyrrol-2-ones with nucleophilic reagents

4-Acetyl-1-alkoxyaryl-5-aryl-3-hydroxy-2,5-dihydro-1H-pyrrol-2-ones reacted with amines to give 1-alkoxyaryl-5-aryl-4-(1-R-aminoethylidene)pyrrolidine-2,3-diones. Reactions of amines with 4-benzoyl-substituted analogs involve nucleophilic attack on the C³ atom in the heteroring to produce the corresponding 3-R-amino-1-alkoxyaryl-5-aryl-4-benzoyl-2,5-dihydro-1H-pyrrol-2-ones. Reactions of the title compounds with hydrazine hydrate, regardless on the substituent on C₄, afforded 4-aryl-3-methyl(phenyl)-5-[2(4)-methoxyphenyl]-4,6-dihydropyrrolo[3,4-c]pyrazol-6-ones.     

Influence of Lewis acids on the facial selectivity in cycloadditions of sugar-derived dihydropyranones

The influence of such Lewis acids as Et₂O·BF₃, ZnCl₂, SnCl₄ and TiCl₄ on the stereochemical course of the Diels-Alder cycloadditions of sugar-derived (2S)-alkoxydihydropyranones was studied. The first two catalysts promoted the addition of dienes to give (3S,4aR,8aS)-3-alkoxy-4a,5,8,8a-tetrahydro-2-benzopyran-4-ones, and their concentration had almost no effect on the stereochemistry of the reaction. In contrast, the concentration of SnCl₄ and TiCl₄ had a remarkable influence on the selectivity, and even facial stereoselection reversal has been observed. These results may be ascribed to chelate complexation of the Lewis acid with the carbonyl and the vicinal alkoxy group of the dihydropyranone.     

Rh/chiral sulfinylphosphine catalyzed asymmetric 1,4-addition of arylboronic acids to chalcones

A general method to obtain enantioenriched 1,3,3-triarylpropan-1-ones bearing a diarylmethine stereocenter was developed using Rh/chiral sulfinylphosphine catalyzed 1,4-addition of arylboronic acids to chalcones. The catalysis progressed smoothly in the presence of 2 mol % catalyst formed in situ from [Rh(C₂H₄)₂Cl]₂ and chiral tert-butanesulfinylphosphine and gave the adducts with up to 99% yield and 98% ee.     

A novel synthesis of bicyclo[3.3.0]oct-1-en-3-ones from cyclobutanones through [chloro(p-tolylsulfinyl)methylidene]cyclobutanes with ring expansion

Treatment of [chloro(p-tolylsulfinyl)methylidene]cyclobutanes, which were synthesized from cyclobutanones and chloromethyl p-tolyl sulfoxide in three steps in high overall yields, with excess cyanomethyllithium gave enaminonitriles in high yields. Heating of these enaminonitriles with H₃PO₄ in acetic acid gave 2-cyanobicyclo[3.3.0]oct-1-en-3-ones in good yield. On the other hand, treatment of the [chloro(p-tolylsulfinyl)methylidene]cyclobutanes with cyanomethyllithium followed by lithium carbanion of the homologues of acetonitrile afforded enaminonitriles having a substituent at the 3-position. Heating of the enaminonitriles with H₃PO₄ in acetic acid gave 2-substituted bicyclo[3.3.0]oct-1-en-3-ones in good to high yields. This method offers a novel and versatile procedure for synthesis of 2-substituted bicyclo[3.3.0]oct-1-en-3-ones from cyclobutanones in good overall yields.     

Reaction of tetracyanoethene with tricarbonyliron complexes of some substituted 7-methylenecycloheptatrienes and the subsequent isomerization of the initial addition products

An NMR study of tetracyanoethene (tcne) addition to substituted (η⁴-7-methylenecycloheptatriene)Fe(CO)₃ complexes shows that 1,3-addition is the dominant initial reaction. Subsequent isomerisation of these 1,3-adducts to 1,6- or 1,8-adducts is controlled by steric factors. Frontier orbital analyses allow concerted pathways to be identified for each observed addition and isomerisation. The crystal structure of the tcne adduct of (η⁴-7-phenylmethylenecycloheptatriene)Fe(CO)₃ establishes an exo geometry for the phenyl substituent.     

A novel method for the synthesis of highly functionalized 3,4-dihydropyrimidin-2(1H)-ones through the 1,4-addition on pyrimidin-2(1H)-ones

A novel method for synthesizing hitherto unreported 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) through 1,4-addition of nucleophiles on pyrimidin-2(1H)-ones is disclosed herein.     

Synthesis and Evaluation of Antioxidant Properties of 2-Substituted Quinazolin-4(3H)-ones

Quinazolinones represent an important scaffold in medicinal chemistry with diverse biological activities. Here, two series of 2-substituted quinazolin-4(3H)-ones were synthesized and evaluated for their antioxidant properties using three different methods, namely DPPH, ABTS and TEAC_CUPRAC, to obtain key information about the structure–antioxidant activity relationships of a diverse set of substituents at position 2 of the main quinazolinone scaffold. Regarding the antioxidant activity, ABTS and TEAC_CUPRAC assays were more sensitive and gave more reliable results than the DPPH assay. To obtain antioxidant activity of 2-phenylquinazolin-4(3H)-one, the presence of at least one hydroxyl group in addition to the methoxy substituent or the second hydroxyl on the phenyl ring in the ortho or para positions is required. An additional ethylene linker between quinazolinone ring and phenolic substituent, present in the second series (compounds 25a and 25b), leads to increased antioxidant activity. Furthermore, in addition to antioxidant activity, the derivatives with two hydroxyl groups in the ortho position on the phenyl ring exhibited metal-chelating properties. Our study represents a successful use of three different antioxidant activity evaluation methods to define 2-(2,3-dihydroxyphenyl)quinazolin-4(3H)-one 21e as a potent antioxidant with promising metal-chelating properties.     

Stereochemical course of the hydrogen migration in the boron trifluoride etherate-catalyzed rearrangement of 1,1-disubstituted epoxides

Mechanistic studies on the BF₃·Et₂O-catalyzed rearrangement of optically active, regioselectively deuterated 1,1-disubstituted epoxides to aldehydic products revealed that the two hydrogens migrate at the migration terminus with opposite stereochemical preferences, i.e. the hydrogen anti to the bulky substituent prefers to migrate with inversion of configuration, whereas the hydrogen syn to the bulky substituent prefers to migrate with retention of configuration.     

Synthesis of novel chiral bidentatephosphite ligands derived from the pyranoside backbone of monosaccharides and their application in the Cu-catalyzed conjugate addition of dialkylzinc to enones

A series of novel bidentatephosphite ligands, derived from methyl 3,6-anhydro-α-d-glucopyranoside and chlorophosphoric acid diaryl ester, were easily synthesized. These ligands were successfully employed in the Cu-catalyzed asymmetric conjugate 1,4-addition of the organozinc reagents diethylzinc and/or dimethylzinc to enones. The stereochemically matched combination of glucopyranoside and (R)-H₈-binaphthyl in ligand 2,4-bis{[(R)-1,1′-H₈-binaphthyl-2,2′-diyl] phosphite}-methyl 3,6-anhydro-α-d-glucopyranoside was essential to afford 85% ee for 3-ethylcyclohexanone with an (S)-configuration in THF, using Cu(OTf)₂ as a catalytic precursor. When the reaction was carried out at lower temperatures, changing from ?10 to ?80 °C, a marginal influence of the temperature on the enantioselectivity of the reaction was observed. The presence of the methyl substituent at the 1-position of the glucopyranoside skeleton had a negative effect on the enantioselectivity in the 1,4-addition of ZnEt₂ to acyclic enones.     

Nucleophilic trifluoromethylation of RF-containing 4-quinolones, 8-aza- and 1-thiochromones with (trifluoromethyl)trimethylsilane

Reactions of N-substituted 2-polyfluoroalkyl-4-quinolones and 8-aza-5,7-dimethyl-2-polyfluoroalkylchromones with (trifluoromethyl)trimethylsilane proceed mainly as a 1,4-nucleophilic trifluoromethylation to give N-substituted 2,2-bis(polyfluoroalkyl)-2,3-dihydroquinolin-4(1H)-ones and 5,7-dimethyl-2,2-bis(polyfluoroalkyl)-2,3-dihydro-4H-pyrano[2,3-b]pyridin-4-ones after acid hydrolysis. Similar reaction with 2-trifluoromethyl-4H-thiochromen-4-one proceeds as a 1,2-addition to give 2,4-bis(trifluoromethyl)-4H-thiochromen-4-yl trimethylsilyl ether.     

Molecular and Solution Structure of 5,6-Benzo-1,3,2-dioxaphosphinin-4-one Derivatives

2-X-5,6-benzo-1,3,2-dioxaphosphinin-4-ones (X = N = C = O, Cl, NEt₂), regardless of their aggregative state, prefer one and the same conformation (flattened sofa); the exocyclic substituent occupies either an axial (N = C = O, NEt₂) or an equatorial (Cl) position.