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Electronic and vibrational circular dichroism (ECD and VCD) spectra and specific optical rotation measurements at the sodium D-line (OR) have been taken for thirteen chiral [2]paracyclo[2](5,8)quinolinophane derivatives and calculated by density functional theory. Besides the planar chirality from the paracyclophane moiety in all molecules, some of the investigated compounds also exhibit central chirality due to an asymmetric carbon atom in the side-chain bound at C-2 of the heterocyclic ring. Characteristic bands for each type of chirality were clearly identified in the VCD spectra in the CH-stretching and mid-IR regions, allowing assignment of absolute and relative configurations. ECD was found to be sensitive mostly, if not exclusively, to planar chirality, whereas OR was also very sensitive to central chirality. Configurational assignment of the different diastereomers by the present method provided results that are in agreement with those inferred from NOE-NMR experiments.

Someone who says "A" should be prepared to also say "B": In contrast to cyclohexane model-based A values, biphenyl model-derived B values are powerful tools to quantify steric repulsion in and conformational behavior of ortho-substituted aromatic compounds.Torsional barriers of 15 ortho-substituted biphenyls have been determined computationally using the B3LYP density functional and experimentally by variable-temperature ("dynamic") nuclear magnetic resonance. Taking advantage of the 3'-isopropyldimethylsilyl group as a novel and superior diastereotopicity probe and tracking coalescence temperatures down to -173 degrees C (100 K), activation energies of aryl-aryl rotation as small as 5 kcal mol(-1) can be assessed. The 2-X/2'-H repulsion increments thus derived are powerful parameters for rationalizing and predicting the conformational behavior of aromatic compounds carrying ortho substituents.

A survey of some recent synthetic approaches to regioselectively fluorinated six member condensed homo- and heteropolycyclic aromatic compounds by complementary cyclization methods is reported.

1-Oxa-2,3-cyclohexadiene (I) can be readily generated by treatment of 5-bromo-3,4-dihydro-2H-pyran with potassium tert-butoxide in the presence of 18-crown-6 and can be trapped with dienes or olefins. Thus, the treatment of I with furan gave 50% yield of Diels-Alder adduct II, whereas with 1,1-diphenylethylene I gave 43% of the [2+2]cycloadduct III. The remarkable regio- and stereoselectivities with which [4+2] and [2+2] adducts are formed suggests a concerted, non-radical cycloaddn. mechanism. [on SciFinder (R)]

Trimethylsilyl dienol ethers are easily oxidized by ceric ammonium nitrate to give α-carbonylallyl radicals which are able to add to enolic carbon-carbon double bonds with very high γ regioselectivity, allowing the method to be applied to the synthesis of 6-oxo-α,β-unsaturated carbonyl compounds.

At the beginning of this article an in-depth comparison of electrophilic and nucleophilic aromatic and heterocyclic substitution processes examines their scopes of applicability in a new light. In the subsequent parts, recent progress in the area of halide and hydride displacement from pyridines is highlighted. Particular attention is paid to the leaving group aptitudes of fluoride and chloride, to the effect of 'passive' substituents on the reaction rates, and to the control of the relative reactivity at halogen-bearing 4-versus 2-(or 6-)positions.

Organic sulfides are selectively oxidized to the corresponding sulfoxides in high yields and under very mild conditions using 35% hydrogen peroxide in CHCl3 in the presence of catalytic amounts of 1, 1, 1-trifluoroacetone.

The CD spectra of a new series of 4-substituted [2.2]paracyclophanes 1b – e have been measured down to 185 nm. Polarizability calculations within the DeVoe model satisfactorily reproduce the CD features over all the spectral range. In addition, the analysis of the complete CD spectrum allowed a phenomenological interpretation of the dependence of the sign of [α] D on the nature of the substituents, at least for X=F, OH, I.

The synthesis of optically active (+)-(R)-[2.2]paracyclophane-[4,5-d]-oxazol-2(3H)-one is described. The aldol reaction of N-acyl derivatives of this planar chiral auxiliary with beazaldehyde occurs with good diastereo- and enantioselectivity.

Regioselectively fluoro-, trifluoromethyl- and trifluoromethoxy-substituted 3-methyleneindolines have been prepared using a four-step procedure involving metalation/bromination of fluorinated Boc-protected anilines, N -propargylation of the resulting o -bromoarylcarbamate and reductive radical cyclization of the product with tributyltin hydride/AIBN. 3-Methyleneindolines, as valuable, versatile intermediates, can be transformed into highly functionalized 3-substituted indoles by ene-type reactions using different enophiles. Thus, fluoro-, trifluoromethyl- and trifluoromethoxy-substituted diethyl 2-hydroxy-2-[(1 H -indol-3-yl)methyl]malonates, ethyl 2-hydroxy-3-(1 H -indol-3-yl)propionates and ethyl 2-hydroxy-3-(1 H -indol-3-yl)-2-trifluormethylpropionates were obtained in 77–86% yield by simply heating the corresponding tert -butyl 3-methyleneindoline-1-carboxylate with an equimolar amount of diethyl ketomalonate, ethyl glyoxalate and ethyl 3,3,3-trifluoropyruvate, respectively, at 100 °C, without solvent, for 0.5–4 h.

Regioisomerically pure trifluoromethyl- and trifluoromethoxy-substituted aromatic and heteroaromatic aldehydes and carboxylic acids are valuable building blocks for the synthesis of biologically active molecules. They have been prepared by employing modern organometallic methods. On this basis, a novel access to 2,3-dihydro-5-(trifluoromethoxy)indole was developed which represents an intriguing example of how organometallic and radical chemistry can fecundate each other.

Das vollstandige Manuskript dieser Zuschrift erscheint in: Angew. Chem. Suppl. 1982, 1853. DOI: 10.1002/ange.198218530

dibromo-5-chloro-2,3-dihydrobenzofuran and anti eliminations from cis- 2,3-dichloro-2,3-dihydrobenzofuran have been investigated in different base-solvent systems. Anti elimination is favored over the syn by a factor of -33 000 in EtONa-EtOH, -10 000 in t-BuOK-t-BuOH, and >10 000 in t-BuOK-t-BuOH, in the presence of 18-crown-6 ether. The rate of both the anti and syn pathway increases with increasing the medium basicity, the syn path being also favored, however to much less extent, by base association. From the values of the deuterium kinetic isotope effect and substituent effect it can be concluded that the transition state structure for the syn elimination from trans2,3-dibromo-2,3-dihydrobenzofuran is significantly affected by base association, but not by medium basicity. trans-2,3-Dihalogeno-2,3-dihydrobenzofurans are very suitable substrates for the study of elimination processes owing to their tendency to be converted by bases into the aromatic benzofuran system. Recently we have investigated the reactions of trans-2,3-dibromo-2,3-dihydrobenzofuran (I) with bromide and chloride ions in dipolar aprotic so1vents.l With bromide ions I is dehalogenated to benzofuran, whereas with chloride ions it gives mainly trans- 2,3-dichloro-2,3dihydrobenzofuran (11)2 together with ca. 10% of 3-bromobenzofuran presumably formed in a syn dehydrobromination process. Syn dehydrohalogenation, however, is the only reaction observed when I or I1 reacts with an alkoxide in the corresponding alcohol. Owing to the increasing importance of syn elimination reactions, it seemed interesting to carry out a detailed kinetic investigation, including the determination of deuterium kinetic isotope effect and substituent effect of the reactions of I and I1 in different alkali alkoxide-alcohol systems. For comparison purposes some anti eliminations from cis -2,3dichloro-2,3-dihydrobenzofuran (111) have also been studied.3 Results and Discussion The eliminations from 1-111, trans-2,3-dibromo-3-deuterio-2,3-dihydrobenzofuran (IV), and trans-2,3-dibromo5-chloro-2,3-dihydrobenzofuran (V) have been studied in EtOK-EtOH, n-BuOK-n-BuOH, t-BuOK-t-BuOH, nRuOK-18C6-n-BuOH (18C6 is 18-crown-6 ether), and t BuOK-18C6-t-BuOH. Some experiments for the reactions of 1-111 in EtONa-EtOH have been also carried out. In each

Les reactions du titre sont realisees sous diverses conditions: a) reaction avec le nitrate d'ammonium cerique (CAN) dans l'acide acetique et l'acetonitrile aqueux ; b) oxydation electrochimique dans l'acetone aqueuse et dans AcOH−CH 3 CN ; c) autooxydation photochimique en presence d'anthracenedicarbonitrile-9,10 ou CAN dans CH 3 CN ; d) oxydation photochimique par CAN dans CH 3 CN

Les β-eliminations syn et anti a partir d'une serie de 31 dihalogeno-2,3 dihydro-2,3 benzofurannes sont etudiees du point de vue cinetique dans t-BuOK-t-BuOH, en presence et en l'absence de 18-crown-6, et dans EtOK-EtOH

1,4-diketones and 4-ketoaldehydes dimethylacetals can be prepared in good yields (65%–82%) by the cerium(IV) ammonium nitrate promoted reaction of ketones with isopropenyl acetate and vinyl acetate, respectively.

Rate ratios were obtained for the base-catalyzed 1,4-dehydrochlorination of (E)- and (Z)-Me3CCCl:C:C:CClCMe3 to give Me3CC.tplbond.CC.tplbond.CCMe3. In the KOMe/MeOH or KOCMe3/Me2SO systems the reactivity of both isomers was similar. With KOCMe3 in Me3COH, THF or C6H6 the 2 isomers exhibited similar reactivity when 18-crown-6 was present, but the E isomer was much more reactive in its absence. These findings suggested a conveyor-belt-type transition state with an aggregate of the base interacting with the H and Cl atoms undergoing elimination. [on SciFinder (R)]

Treatment of the title compound with chloride ions in acetonitrile leads mainly to the formation of trans-2,3-dichloro-2,3-dihydrobenzofuran. Since a nucleophilic displacement of bromide anion by chloride anion can be excluded, a mechanism involving the equilibrium 2Cl− + Br2 ⇋ 2Br− + Cl2 is suggested.