exo-Stereoselectivity in Diels-Alder Addition of Halogenocyclopropenes to Butadienes and Furans

The stereochemistry of the Diels-Alder reaction of 1,2-dichloro-3,3-difluorocyclopropene ( 5a ) to 1,4-diphenyl-1,3-butadiene ( 6 ) and 1,3-diphenylisobenzofuran ( 7 ) was unambiguously established by X-ray structure determination. In all cases known so far, tetrahalogenocyclopropenes add exo to open-chain dienes and furans. The previously reported exo-addition product ( 2a ) of l-bromo-2-chlorocyclopropene ( 5b ) to 7 allows assignments of the stereochemistry of other additions of 5b to furans. exo-Addition usually predominates, but in some cases endo- adducts are also formed. This contrasts with reports in the literature that 5b adds preferentially endo to open-chain dienes.     

Face Selectivity of the Diels-Alder Additions of Exocyclic Dienes Grafted onto 7-Oxabicyclo[2.2.1]heptanes

Stereoselective syntheses of 2exo, 3exo-bis (chloromethyl)-5-[(Z)-chloromethylidene]- ( 9 ), 2exo, 3exo-bis (chloromethyl)5-[(E)-chloromethylidene]- ( 10 ) and 2exo, 3exo-bis(chloromethyl)-5-[(E)-methoxymethylidene]-6-niethylidene-7-oxa-bicyclo[2.2.1]heptane ( 13 ) are presented. Double elimination of HCI from 9, 10 and 13 yielded 2-[(Z)-chloromethylidene]- ( 14 ), 2-[(E)chloromethylidene]- ( 15 ) and 2-[(E)-methoxymethylidene]-3,5,6-mmethylidene-7-oxabicycio[2.2.1]heptane ( 18 ), respectively, without loss of the olefin configuration. Ethylene tetracarbonitrile (TCE) and N-phenyltriazolinedione (NPTAD) added to these new exocyclic dienes and tetraenes preferentially onto their exo-face. The same face selectivity was observed for the cycloadditions of TCE to the (Z)- and (E)-chlorodienes 9 and 10 , thus realizing a case where the kinetic stereoselectivity of the additions is proven not to be governed by the stability of the adducts. The exo-face selectivity of the Diels-Alder additions of dienes grafted onto 7-oxabicyclo [2,2.1]heptanes contrasts with the endo-face selectivity reported for a large number of cycloadditions of dienes grafted onto bicyclo[2.2.1]heptane skeletons.     

Ni‐Catalyzed Asymmetric Cycloisomerization of Dienes by Using TADDOL Phosphoramidites

A library of α,α,α,α‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol (TADDOL)‐based phosphoramidites has been synthesized and applied in the Ni‐catalyzed cycloisomerization of different dienes. Through the systematic variation of the three structural motifs of the lead structure, that is, the amine moiety, the protecting group, and the aryl substituents, the ligand features could be optimized for the asymmetric cycloisomerization of the model substrate diethyl diallylmalonate. The substrate scope of the new catalytic system was extended to other diallylic substrates, including unsymmetrical dienes. Overall remarkably high activities of up to approximately 13 500 h^?1, very high selectivities toward five‐membered exo‐methylenecyclopentanes, and enantioselectivities of up to 92 % ee have been achieved.     

Dynamique Moléculaire des Chloro-4 et Bromo-4 Méthylènecyclohexanes par Résonance Magnétique Nucléaire du 13C

Kinetic parameters are obtained for ring inversion of 4-chloro- and 4-bromo-1-methylenecyclohexanes by observation of ¹³C and ¹H NMR spectra as a function of sample temperature. Cl and Br substituents show similar effects on the inversion barrier in the exo-methylene system and in the parent cyclohexane.     

13C FT-NMR spectra of alkyl substituted furans. A study of the influence of steric interactions

The ¹³C FT-NMR spectra of thirteen furans, monodi- or trisubstituted with methyl and/or t-butyl groups, were studied in detail. Substituent effects of methyl and t-butyl groups on the chemical shifts of ring carbon atoms are additive in nonsterically hindered furans. Steric shifts for the ring carbon atoms are found in furans with bulky neighbouring substituents, but the hybridisation of the carbon atoms in these hindered furans is not changed. The chemical shifts of the substituents are calculated according to the Grant-Cheney formula. No simple relationship between steric shift and steric hindrance can be ascertained.     

13C NMR and force field investigations of hydrindane conformations

¹³C NMR shifts of trans- and cis-annelated bicyclo[4.3.0]nonanes with substituents R in position 8 (R ? H, OH, Cl, Br) and 1-hydroxy derivatives were analysed on the basis of force field calculated torsional angles using Allinger's MM1 program. Shielding increments for the 6 membered ring agree with corresponding cyclohexane values within ± 0.8 ppm maximal deviation. ¹³C NMR line shape analysis with cis-hydrindane between 148 and 180 K yielded ΔH* = 37.0 ± 0.4 kJ mol^?1 and ΔS* = 28 J mol^?1 K^?1 for the topomerization. The force field calculated reaction profile showed ΔH* = 37 kJ mol^?1, in close agreement.     

Carbon-13 n.m.r. studies. 65—13C spectra of some tricyclo[3.2.1.02,4]octane derivatives

The ¹³C n.m.r. spectra of 18 derivatives of the tricyclo[3.2.1.0^2,4]octanes have been determined. This series includes methyl, hydroxyl and oxo substituted examples to compare the effects of these substituents on the skeletal carbon shieldings with those observed for the corresponding norbornanes and bicyclo[3.2.1]octanes. In general, the trends are similar and the perturbations associated with closely neighboring groups follow a consistent pattern. The shielding data for the exo–exo and exo–endo isomers of tetracyclo[3.3.1.0^2,40^6,8]nonane are also reported.     

The Effects of Homoconjugated Cyclopropane and Oxirane Rings on the Diels-Alder Reactivity of 2,3-bis (methylidene)norbornane

Preparation of 6exo, 7exo-bis (methylidene)-tricyclo[3.2.1.0^2,4]octane ( 6 ) is described. The reactivity of 6 towards tetracyanoethylene is evaluated and compared with that of exo-2,3-epoxy-5,6-bis (methylidene)norbornane ( 5 ), 2,3-bis-(methylidene)norbornane ( 1 ) and other related dienes. The cyclopropane group in 6 exerts an unsignificant rate retardation effect on the Diels-Alder reactivity of this diene relative to that of 1 , whereas a relatively important rate retardation effect is caused by the exo-oxirane ring in 5 . The observed effects are probably due to electronic factors (through-space and through-bond interactions).     

Furan derivatives. Part 8 On substituent effects in the synthesis of 4,5-dihydro-3H-naphtho[1,8-bc]furans

4,5-Dihydro-3H-naphtho[1,8-bc]furans 4 and 6 which have various substituents (R¹ and R²) have been synthesized from 8-oxo-5,6,7,8-tetrahydro-1-naphthyloxyacetic acids 1 and 3 or their ethyl esters 2 . The reaction of acids 1 and 3 with sodium acetate in acetic anhydride gave a mixture of furans 4 and 6 and lactones 5 and 7 . The ratios of the products were varied according to the types of substituents (R¹ and R²) in acids 1 and 3 . As the substituent R¹ (R² = hydrogen) in acids 1 was changed from hydrogen to a methyl, ethyl or isopropyl group, production of furans 4 became more difficult. However, when a phenyl group was used as the substituent, furan 4 was obtained in good yield. Similarly, as the substituent R² (R¹ = hydrogen) in acids 1 was changed from hydrogen to a methyl, ethyl or isopropyl group, furan formation was more difficult. In contrast, acids 3 which had electron-withdrawing substituents such as chlorine, bromine or a nitro group at the 4-position afforded furans 6 in good yield. 4,5-Dihydro-3H-naphtho[1,8-bc]furans 4 and 4,5-dihydro-3H-naphtho[1,8-bc]furan-2-carbocylic acids 8 were synthesized from the reaction of esters 2 and potassium hydroxide in dioxane. When the substituents R¹ or R² in esters 2 were varied from hydrogen to a methyl, ethyl or isopropyl group the total yields of furans 4 and furancarboxylic acids 8 were reduced.     

The structural dependence of vicinal 13C?13C coupling constants in s-cis-butane and cis-butane

The dependence of three-bond ¹³C-¹³C couplings of cis-butane and cis-butene on the valence angle, the torsional angle of the methyl groups and methyl and methylene substituents is discussed on the basis of INDO-SCPT calculations. The results support the interpretation of the experimental couplings between the bridgehead carbons of bicyclic hydrocarbons based on a multiple-path mechanism.     

Carbon-13 magnetic resonance studies of cyclic compounds. 2. Carbon-13 chemical shift parameters for equatorial and axial substituents in cyclohexane: The substituents methyl,ethyl, isopropyl,methoxy and phthalimido

Carbon-13 chemical shift parameters for equatorial and axial substituents in cyclohexane are reported for methyl, ethyl, isopropyl, methoxy and phthalimido substituents. The usefulness of the alkyl parameters is demonstrated by the agreement between calculated and observed ¹³C shifts for trans-1,4-dialkylcyclohexanes (alkyl = Me, Et, i-Pr) and for both conformations of cis-1,4-dialkylcyclohexanes (alkyl = Me, Et, i-Pr).     

Phthalocyaninate und Tetraphenylporphyrinate von hochkoordiniertem ZrIV/HfIV mit Hydroxo‐, Chloro‐, (Di)Phenolato‐, (Hydrogen)Carbonato‐ sowie (Amino)Carboxylato‐Liganden

Phthalocyaninates and Tetraphenylporphyrinates of High Co‐ordinated Zr^IV/Hf^IV with Hydroxo, Chloro, (Di)Phenolato, (Hydrogen)Carbonato, and (Amino)Carboxylato Ligands Crystals of tetra(n‐butyl)ammonium cis‐tri(phenolato)phthalocyaninato(2‐)zirconate(IV) ( 2 ) and ‐hafnate(IV) ( 1 ), di(tetra(n‐butyl)ammonium) cis‐di(tetrachlorocatecholato(O, O')phthalocyaninato(2‐)zirconate(IV) ( 3 ), and cis‐(di(μ‐alaninato(O, O')di(μ‐hydroxo))di(phthalocyaninato(2‐)zirconium(IV)) ( 12 ) have been isolated from tetra(n‐butyl)ammonium hydroxide solutions of cis‐di(chloro)phthalocyaninato(2‐)zirconium(IV) and ‐hafnium(IV), respectively, and the corresponding acid in polar organic solvents. Similarly, with cis‐di(chloro)tetraphenylporphyrinato(2‐)zirconium(IV), ^cis[Zr(Cl)₂tpp] as precursor crystalline tetra(n‐butyl)ammoniumcis‐tetrachlorocatecholato(O, O')hydrogentetrachlorocatecholato(O)tetraphenylporphyrinato(2‐)zirconate(IV) ( 4 ), cis‐hydrogencarbonato(O, O')phenolatotetraphenylporphyrinato(2‐)zirconium(IV) ( 6 ), cis‐di(benzoato(O, O'))tetraphenylporphyrinato(2‐)zirconium(IV) ( 11 ), and cis‐tetra(μ‐hydroxo)di(tetraphenylporphyrinato(2‐)zirconium(IV)) ( 13 ) with a cis‐arrangement of the symmetry equivalent μ‐hydroxo ligands, and from di(acetato)tetraphenylporphyrinato(2‐)zirconium(IV) the corresponding trans‐isomer ( 14 ) have been prepared. The endothermic dehydration at 215 °C of 13/14 yields μ‐oxodi(μ‐hydroxo)di(tetraphenylporphyrinato(2‐)zirconium(IV)) ( 15 ). 15 also precipitates on dilution of a solution of ^cis[Zr(X)₂tpp] (X = Cl, OAc) in dmf/(ⁿBu₄N)OH with water, while on prolonged standing of this solution on air tri(tetra(n‐butyl)ammonium) cis‐(^nido〈di(carbonato(O, O'))undecaaquamethoxide〉tetraphenylporphyrinato(2‐)zirconate(IV) ( 7 ) crystallizes, in which Zr^IV coordinates a supramolecular nestlike ^nido〈(O₂CO)₂(H₂O)₁₁OCH₃〉^5— cluster anion stabilised by hydrogen bonding in a nanocage of surrounding (ⁿBu₄N)⁺ cations. On the other hand, ^cis[Zr(Cl)₂pc] forms with (Et₄N)₂CO₃ in dichloromethane di(tetraethylammonium) cis‐di(carbonato(O, O')phthalocyaninato(2‐)zirconate(IV) ( 5 ). ^cis[Zr(Cl)₂tpp] dissolves in various O‐donor solvents, from which cis‐di(chloro)dimethylformamidetetraphenylporphyrinato(2‐)zirconium(IV) ( 8 ), cis‐di(chloro)dimethylsulfoxidetetraphenylporphyrinato(2‐)zirconium(IV) ( 9 ), and a 1:1 mixture ( 10 ) of cis‐di(chloro)dimethylsulfoxidetetraphenylporphyrinato(2‐)zirconium(IV) ( 10a ) and cis‐chlorodi(dimethylsulfoxide)tetraphenylporphyrinato(2‐)zirconium(IV) chloride ( 10b ) crystallize. All complexes contain solvate molecules in the solid state, except 3 . Zr^IV/Hf^IV is directed by ∼1Å out of the plane of the tetrapyrrolic ligand (pc, tpp) towards the mutually cis‐coordinated axial ligands. In the more concavely distorted phthalocyaninates, Zr^IV is mainly eight‐coordinated and in the tetraphenylporphyrinates seven‐coordinated. The octa‐coordinated Zr atom is in a distorted quadratic antiprism, and the hepta‐coordinated one is in a square‐base‐trigonal‐cap cooordination polyhedron. In most tpp complexes, the Zr atom is displaced by up to 0.3Å out of the centre of the coordination polyhedron towards the tetrapyrrolic ligand. In 13/14 , both antiprisms are face shared by an O₄ plane, and in 12 they are shared by an O₂ edge and the O atoms of the bridging aminocarboxylates, the dihedral angle between the O₄ planes of both antiprisms being 50.1(1)°. The mean Zr‐N_p distance is 0.05Å longer in the pc complexes than in the tpp complexes (d(Zr‐N_p)_pc = 2.31Å). In the monophenolato complexes, the mean Zr‐O distance (∼2.00Å) is shorter than in the complexes with other O‐donor ligands (d(Zr‐O)_pc = 2.18Å; d(Zr‐O)_tpp = 2.21Å); the Zr‐Cl distances vary between 2.473(1) and 2.559(2)Å (d(Zr‐Cl)_tpp = 2.51Å). d(C‐O_exo) = 1.494(4)Å in the bidentate hydrogencarbonato ligand in 6 is 0.26Å longer than in the bidentate carbonato ligands in 5 and 7 . 9 and 10a are rotamers slightly differing by the orientation of the axial ligands with respect to the tpp ligand. In 1—4, 6 , and 11 the phenolato, catecholato, and benzoato ligands, respectively, are in syn‐ and/or anti‐conformations with respect to the plane of the macrocycle. π‐Dimers with modest overlap of the neighbouring macrocyclic rings are observed in 5, 6, 8, 9, 10b, 12 , and 14 . The common UV/Vis spectroscopical and vibrational properties of the new phthalocyaninates and tetraphenylporphyrinates scarcely reflect their rich structural diversity.     

The structure of hydantoins in solution and in the solid state

The results of NMR spectroscopic and X-ray crystallographic studies are critically discussed with respect to the structure of hydantoins, their tautomerism, and their acidity. The imide NH proton of the preferred, nearly planar 2,4-imidazolidine-dione tautomer proved to be more acidic than the corresponding amide NH proton. Phenyl substituents at the ring nitrogen atoms and at C-5 are twisted from the plane of the hydantoin ring; in case ofortho substituents restricted rotation about the N-aryl bond was found and the barrier to rotation determined by dynamic NMR spectroscopy. For 5-benzyl substituents, afolded conformation of the two rings, due to intramolecular interactions, was found and for 5-exo-methylene substituted hydantoins the relevant E/Z isomerism at theexo-cyclic C, C double bond was studied. In addition, the¹H and¹³C chemical shifts of the hydantoins proved to excellently indicate the electronic distribution along the hydantoin ring moiety. Finally, the mass spectrometric fragmentation of the hydantoins is critically discussed.Dedicated to Prof. Rolf Borsdorf on the occasion of his 65th birthday.     

13C NMR shifts and conformations of substituted indans

¹³C NMR spectra of indan derivatives bearing substituents in the 1, 2, 5 and 6 positions are reported and assigned by LIS measurements and other techniques. Epimeric indanes bearing vicinal oxygen and phenyl or benzyl substituents show ring carbon shielding in the cis relative to the trans isomers, which is compared with corresponding cyclopentane shifts, and indicates the predominance of envelope conformations with pseudoaxial oxygen substituents for the cis isomers. Acetylation shifts show consistently larger shielding at C-β for the trans compounds. Introduction of oxygen at C-5 leads to asymmetric shielding effects at the ortho carbon atoms as soon as there is a substituent in the para position which can participate in mesomeric forms.     

On the Tacticity of Polynorbornenes with 5,6‐endo Pendant Groups That Contain Substituted Aryl Chromophores

Two dimers and a series of polymers with 5,6‐endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and ¹³C NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the ¹³C NMR spectra when the substituents are electron‐withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, ε_d, was linearly related to the Hammett constant σ. Polynorbornenes with electron‐withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular.     

Photoinduced Double Addition of Acetylene to 3-Oxocyclopent-1-ene-1-carbonitrile or 3-oxocyclopent-1-enyl acetate leading to 2,3-dihydro-1H-inden-1-one and other rearranged products

UV Irradiation of 3-oxocyclopent-1-enyl acetate ( 17 ) and acetylene in MeCN at 0° gives, besides the product of normal enone-alkyne [2 + 2] cycloaddition (cis-4-oxobicyclo[3.2.0] hept-6-en-1-yl acetate, 18 ) and its product of oxa-di-π-methane rearrangement (5-oxotricyclo[4.1.0.0^2,7]hept-2-yl acetate, 19 ), unexpected products of further addition of a molar equivalent of acetylene. These are indanone ( = 2,3-dihydro-1H-inden-1-one, 16 ), in 21% yield, cis-1-cisoid-1,2-cis-2- ( 20 ) and cis-1-transoid-1,2-cis-2-7-oxotricyclo[4.3.0.0^2,5]non-3-en-1-yl acetate ( 21 ), 4-oxo-7-‘exo’-vinyltricyclo[3.2.0.0^2,6]hept-2-yl acetate ( 22 ), cis-4-oxo-6-‘endo’- ( 23 ) and cis-4-oxo-6-‘exo’-vinylbicyclo[3.2.0]hept-1-yl acetate ( 24 ), and cis-4-oxo-7-‘exo’-vinylbicyclo[3.2.0]hept-1-yl acetate ( 25 ). At least in part, indanone must be formed via intermediates 20 and 21 . In fact, on heating a 9:1 mixture 20/21 , indanone is obtained quantitatively. With 3-oxocyclopent-1-ene-1-carbonitrile ( 15 ) in place of 17 , indanone is formed in lower (8%) yield besides much tars.     

Spectroscopic and Electrochemical Studies of the Interaction of Some Gold(III) Complexes with Biologically Relevant Thiones

The interaction of gold(III) complexes, [Au(cis‐DACH)Cl₂]Cl and [Au(cis‐DACH)₂]Cl₃ complexes (DACH = cis‐1,2‐diaminocyclohexane), with ¹³C, ¹⁵N‐enriched thiourea (Tu) and 1,3‐diazinane‐2‐thione ligands was investigated. The progress of these reactions was monitored by NMR (¹H, ¹³C, and ¹⁵N) and UV–vis spectroscopy as well as square wave stripping voltammetry. The kinetic studies of the substitution reactions between the above‐mentioned complexes with thiones in aqueous solutions containing 30 mM KCl, which is used to suppress the hydrolysis of the chloride complexes, were conducted. These reactions were followed under pseudo–first‐order conditions as functions of ligand concentration, pH, and temperature. The activation parameters (ΔH^#, ΔS^#) were calculated from Eyring plots, and the negative values of ΔS^≠ lend support for an associative mechanism. The kinetic data also indicated a relatively higher reactivity of [Au(cis‐DACH)Cl₂]Cl than that of [Au(cis‐DACH)₂]Cl₃ toward the thiones.     

New N-(Arylsulfonyl)-5-aminomethylbicyclo[2.2.1]hept-2-enes. Synthesis, 1H and 13C NMR Spectra,and Chemical Reactions

A synthesis of new N-(arylsulfonyl)-5-aminomethylbicyclo[2.2.1]hept-2-enes obtained by reaction of stereoisomeric exo- and endo-5-aminomethylbicyclo[2.2.1]hept-2-enes with arylsulfonyl chlorides is described. With the use of the data of ¹H and ¹³C NMR spectra, including those of two-dimensional spectra recorded in COSY and NOESY mode, the contribution of stereochemical features of sulfonamides into the spectra structure of endo- and exo-isomers was evaluated. Applying various methods of the phase-transfer catalysis alkylation and acylation of the stereoisomeric arylsulfonamides containing a norbornene fragment was carried out. The reactions of alkylated stereoisomeric sulfonamides, N-(benzyl)-N-(3,4-dichlorophenylsulfonyl)-5-aminomethylbicyclo[2.2.1]hept-2-enes, with peroxyphthalic acid provide epoxides; the orientation of substituents in the cage norbornene fragment does not affect the direction of the process. The structure of the products obtained by sulfonamides transformations was confirmed by IR, ¹H and ¹³C NMR spectra.     

NMR and kinetic studies of the interactions of [Au(cis-DACH)Cl2]Cl and [Au(cis-DACH)2]Cl3 with potassium cyanide in aqueous solution

The interactions of [Au(cis-DACH)Cl₂]Cl and [Au(cis-DACH)₂]Cl₃ [where cis-DACH is cis-1,2-diaminocyclohexane] with enriched KCN were carried out in CD₃OD and D₂O, respectively. The reaction pathways of these complexes were studied by ¹H, ¹³C, ¹⁵N NMR, UV spectrophotometry, and electrochemistry. The kinetic data for the reaction of cyanide with [Au(cis-DACH)₂]Cl₃ are k = 18 M^?1s^?1, ?H^≠ = 11 kJ M^?1, ?S^≠ = ?185 JK^?1 M^?1, and E_a = 13 kJ M^?1 with square wave voltammetric (SWV) peak +1.35 V, whereas the kinetic data for the reaction of cyanide ion with [Au(cis-DACH)Cl₂]Cl are k = 148 M^?1s^?1, ?H^≠ = 39 kJM^?1, ?S^≠ = ?80 JK^-1 M^?1, and E_a = 42 kJM^?1 along with SWV peak +0.82 V, indicating much higher reactivity of [Au(cis-DACH)Cl₂]Cl toward cyanide than [Au(cis-DACH)₂]Cl₃. The interaction of these complexes with potassium cyanide resulted in an unstable [Au(¹³CN)₄]^? species which readily underwent reductive elimination reaction to generate [Au(¹³CN)₂]^? and cyanogen.     

Norbornanes. Part 10. Solvolysis of the Stereoisomeric 6-Cyano-2-norbornyl p-Toluenesulfonates. A Correction

The solvolysis products of the stereoisomeric 6-cyano-2-norbornyl p-toluene sulfonates 1 - 4 (R ? CN) in dioxane/water 7 : 3 have been determined. In contrast to an earlier report the 6exo-cyano-2exo-norbornyl p-toluenesulfonate ( 1 ; R?CN) yields 30% of the 2endo-alcohol 9 (R?CN) beside the 2exo-alcohol 10 and the norbornenes 12 and 13. The results confirm that - I substituents at C(6) reduce 1,3-bridging in the intermediate norbornyl cation and hence its rate of rearrangement. The relatively high rate constants for some 6-fluoro- and 6-cyano-2exo norbornyl p-toluenesulfonates are ascribed to C, C-hyperconjugation assisted by the conjugative effects of the 6-fluoro and cyano substituents.