Studies of Diastereoselectivity in Diels-Alder Reactions of (S)S-4a,5,8,8a-Tetrahydro-5,8-methane-2-(p-tolylsulfinyl)-1,4-naphtho- quinones with Cyclopentadiene

The title compounds 6 and 7 have proved to be adequate rigid models to evaluate the ability of the sulfinyl group to control the diastereoselectivity of the [4 + 2] cycloadditions of cyclopentadiene on the ene-dione moiety. The results of thermal and Lewis acid-catalyzed reactions allowed us to establish that both reactivity and endo/exo selectivity were modulated by the presence of the sulfinyl group, the endo-anti-endo or the exo-anti-endo bisadducts being obtained as major products depending on experimental conditions. The role of the association between the SOTol group and several Lewis acids (BF(3).OEt(2), Eu(fod)(3), ZnBr(2)), which shifted the conformational equilibrium around the C-S bond, was used to explain the stereochemical course of the cycloadditions mainly controlled by steric factors. The synthesis of the exo-anti-endo bisadduct 5 was described for the first time.     

Reactions of 2-Deoxy-4, 5-O-Isopropylidene-D-Erythro- and D-Threo-Pent-1-Enose Derivatives

ABSTRACT

The reactivity of the title compounds has been studied toward different nucleophiles and electrophiles. Unlike other ketene dithioacetals, compounds 3-5 did not add nucleophiles to the double bond. Instead, in the presence of Lewis acids they underwent substitution reaction at position 3. If the nucleophile was not strong enough, formation of 6 and 7 were observed. With 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose (18), a 3:1 mixture of 11 and 12 was formed from 4. These observations may be interpreted in terms of easy formation of the allylic carbocation I which gives diastereomers with nucleophiles. However, this allylic ether-like behaviour was ruled out by the fact that compounds 9 and 10 did not undergo [2,3] sigmatropic rearrangement with lithium diisopropylamide. With N-bromosuccinimide compound 3 gave the 2-bromo derivative 8. Compounds 3 and 8 resisted common mercury salt assisted demercaptalization procedures.     

Intramolecular Diels-Alder Reactions via 3-(Phenylthio)-4-(Trimethylsilyl)-3-Sulfolene

Deprotonation of the title compound 2 followed by treatment with 5-iodo-1-pentene or 6-iodo-l-hexene gave the alkylated products 3 and 4 which upon refluxing in toluene yielded the dienes 8a and 8b. Intramolecular Diels-Alder reactions were achieved by heating the dienes 8a and 8b in toluene in a sealed tube at 160–180°C to give bicyclo[4.3.0]nonene 9 and bicyclo[4.4.0]decene 10, respectively, in good yield. The stereochemistry of the cyclization products was determined, and was rationalized by comparison of the possible transition states involved.     

Stereoselective Synthesis and Diels-Alder Reactions of (Z)- and (E)-1,2-bis(Phenylthio)-1,3-Butadiene

Bromination of 3-phenylthio-2-sulfolene (2) with N-bromosuccinimide gave 2-bromo-3-phenylthio-2-sulfolene (3) which was converted mainly to 2,3-bis(phenylthio)-2-sulfolene (4) by treatment with sodium phenylthiolate. Thermal desulfonylation of 4 at different temperatures in the presence of a base (DBU) yielded stereoselectively the (Z)- and (E)-1,2-bis(phenylthio)-1,3-butadiene (6). These two geometric isomers could be thermally interconverted. The Diels-Alder reactions of 6 were also investigated. Only the (Z)-diene 6a could undergo the Diels-Alder reaction; the (E)-diene 6b was in situ converted to the Z isomer before undergoing (he Diels-Alder reaction. The reaction of 6a with N-phenylmaleimide gave the cycloaddition product 7 with complete endo selectivity, but under daylight or during chromatography it readily underwent a thioallylic rearrangement to yield 8 with inversion of configuration. The cycloaddition of 6a with methyl acrylate proceeded regiospecifically, but generating a mixture of endo and exo isomers. The endo/exo ratio could be increased by using ZnCl₂ as the catalyst.     

Diels-Alder reactions of N-acyl-2-alkyl(aryl)-5-vinyl-2,3-dihydro-4-pyridones

Readily available N-acyl-5-vinyl-2,3-dihydro-4-pyridones undergo Diels-Alder cyclization with various dienophiles to afford novel octahydroquinolines containing synthetically useful functionality. With dihydropyridone 5 and cis-disubstituted dienophiles, the resulting cycloadducts were obtained as single diastereomers in good to excellent yield. The corresponding reaction of 5 with methyl acrylate, acrylonitrile, and phenyl vinyl sulfone showed modest preference for the endo adducts. The effect of the dihydropyridone C-2 and C-4 substituents on the degree of diastereofacial control was examined. By using this methodology, the core decahydroquinoline skeleton of gephyrotoxin was prepared in a stereocontrolled fashion. Interesting reactivity was observed with certain dienophiles leading to ring-opening of the initially formed cycloadducts. This tandem reaction provides a route to uniquely substituted beta-aminoketones, alcohols, and unnatural amino acids.     

Reactions of (E)-4-Stilbenethiole with Dibromoalkanes

New substituted stilbenes have been prepared by reactions of (E)-4-stilbenethiole with dibromoalkanes. ¹H and ¹³C NMR spectra of new compounds have been assigned unambiguously on the basis of a combination of homo- (¹H?¹H COSY) and heteronuclear (¹ H?¹³C COSY-HETCOR) two-dimensional methods, chemical shifts, and spin-coupling constants.     

Synthese des 1-(2,3-Dimethoxybenzyl)-5,6-dimethoxyisochinolins

Ohne Zusammenfassung     

Crystal and Molecular Structure of 2H- and 2-(p-Tolylamino)-5,6-dimethylthieno[2,3-d]pyrimidin-4-ones

The crystal and molecular structure of 2H- and 2-(p-tolylamino)-5,6-dimethylthieno[2,3-d]pyrimidin-4-ones was investigated by X-ray diffraction. In crystals, the tautomeric form with a localized N(1)=C(2) bond is realized. A comparative analysis of the two structures using the literature data is given to examine the conjugation effect on the geometrical parameters of a pseudoaromatic pyrimidine system.     

Reactions of polyhalogenopyridines. 12. Reactions of 4-pentafluoroethylthio-2,3, 5,6-tetrafluoropyridine with nucleophilic agents

The reactions of 4-perfluoroethylthio-2,3,5,6-tetrafluoropyridine with various nucleophilic agents were investigated. It was shown that the pentafluoroethylthio group is inert toward N- and O-nucleophiles.For Communication 11, see [1].Chernogolovka Institute of Chemical Physics, Russian Academy of Sciences, Chernogolovka. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 932–935, July, 1996. Original article submitted June 22, 1996.     

Thermal oligomerization of methyl 4-(1,3-dioxo-2,3-dihydro-1H-isoindol-2-yl)buta-2,3-dienoate

Dimeric compounds formed as a result of thermal oligomerization of methyl 4-(1,3-dioxo-2,3- dihydro-1H-isoindol-2-yl)buta-2,3-dienoate were identified.     

Synthesis and Crystal Structure of（2E,6E）-2,6-bis（2,3-dimethoxybenzylidene）cyclohexanone

The new title compound (2E,6E)-2,6-bis(2,3-dimethoxybenzylidene)cyclohexanone (C 24 H 26 O 5,M r=394.45) has been synthesized,and its crystal structure was studied.The title compound crystallizes in the orthorhombic system,space group Pca2 1 with a=17.536(2),b=14.8515(16),c=8.0512(9),V=2096.8(4) 3,Z=4,D c=1.250 g/cm 3,λ=0.71073,μ=0.087 mm-1 and F(000)=840.The structure was solved by direct methods and refined to R=0.0533 and wR=0.1248 from 2727 observed reflections (I > 2σ(Ⅰ)).The title molecules are connected through hydrogen bonds to generate a 3-D supramolecule.The preliminary biological tests showed definitely biological activity for the title compound.     

Reactions of (4E)-3-Arylamino-4-(hydroxyimino)naphthalen-1(4H)-ones and (4E)-2-[Arylamino(alkylamino)]-4-(hydroxyimino)naphthalen-1(4H)-ones with 2,2-Dihydroxyindane-1,3-dione

Russian Journal of Organic Chemistry - The reactions of 3-arylamino-1,4-naphthoquinone-4-oximes with 2,2-dihydroxyindane-1,3-dione proceed without involving the oxime group and lead to...     

Catalytic Enantioselective Reactions. Part VIII. Catalytic Enantioselective Addition of Diethylzinc to Aldehydes Using (2S,3S)-(-)-1,4-Diamino-2,3-Butanediol Derivatives as Chiral Catalysts

A series of new chiral β-N,N-dialkylaminoalcohol derivatives with an axis of C₂ symmetry was prepared from diethyl L-tartrate and their enantioselectivities as chiral catalysts for enantioselective addition of diethylzinc to aldehydes were compared.     

Asymmetric Diels-Alder Reactions of Cyclopentadiene with N-Crotonoyl- and N-Acryloyl-4,4-Dimethyl-1,3-Oxazolidin-2-one,Mediated by Chiral Lewis Acids

One-pot Diels-Alder reactions of cyclopentadiene with 3-crotonoyl- ( 2 ) and 3-acryloyl-4,4-dimethyl-1,3-oxazolidin-2-one ( 3 ), Mediated by chiral Lewis acids, are described. AlCl₃, EtAlCl₂, Et₂AlCl, TiCl₄, ZrCl₄, SnCl₄, SiCl₄, and BBr₃, modified with derivatives of D -mannitol, L -tartaric acid, and (R)-binaphthol, were applied as chiral promotors. The reaction with dienophile 2 , carried out in CH₂Cl₂ at ?78° with high yield, was characterized by excellent π-face selectivity. In case of the reaction with dienophile 3 , the efficiency of the chirality transfer was much lower.