Studies in stereochemistry—I Stereospecific routes to trans- anti- and cis- syn-Δ-dodecahydrophenanthrenes

Reduction of trans-1-oxo-7-methoxy-1,2,3,4,9,10,11,12-octahydrophenanthrene (XI) by lithium tri-t-butoxyaluminohydride gave trans-1β-hydroxy-7-methoxy-1,2,3,4,9,10,11,12-octahydrophenanthrene (XII) which on lithium—liquid ammonia reduction gave trans-anti-1β-hydroxy-7-oxo-Δ⁸⁽¹⁴⁾-dodecahydrophenanthrene (XIII). Reduction of cis-1-oxo-7-methoxy-1,2,3,4,9,10,11,12-octahydrophenanthrene (XV) by sodium borohydride gave cis-1-hydroxy-7-methoxy-1,2,3,4,9,10,11,12-octahydrophenanthrene (XVI) which on lithium—liquid ammonia reduction gave cis-syn-1-hydroxy-7-oxo-Δ⁸⁽¹⁴⁾-dodecahydrophenanthrene (XVII).     

The absolute configuration of trans-1,2-dimethylcyclopropane

By application of the newly discovered fact that 1° alkyl chlorides with γ-hydrogen form cyclopropanes on treatment with sodium metal, (−)-trans-1,2-dimethylcyclopropane has been prepared from (+)-1-chloro-2-methylbutane. Rigorous assignment of configuration to the isomeric cis- and trans-dimethylcyclopropanes is thereby achieved. The absolute configuration, (1R : 2R) trans-1,2-dimethylcyclopropane, can be assigned to the (−) enantiomer by several lines of argument and agrees with that calculated by Fitts.     

X-ray study of the hetero ring flexibility in trans-5,6- trimethylene- and tetramethylene-5,6-dihydro 2-phenyl-[4H]-1,3-thiazines

The structures to two 1,3-thiazine derivatives differing only in the number of CH₂ groups in their trans fused hydrocarbon ring (_n = 3 for I and n = 4 for II) have been established by X-ray crystallography from diffractometer data. Crystals of I (trans-5,6- trimethylene-5,6-dihydro-2-phenyl-[4H] - 1,3-thiazine) are triclinic, space group P with a = 7.661(1), b = 8.282(1), c = 9.566(2) Å, = 91.75(1), β = 100.72(1), γ = 105.45(1)° Z = 2, D_c = 1.260 g cm^-3. Crystals of II (trans-5,6-tetramethylene-5,6-dihydro-2-phenyl [4H]-1,3-thiazine) are monoclinic, space group P2₁/c with a = 7.914(2), b = 19.362(13), c = 8.440(1) Å, β = 109.16(2)°C Z = 4, D_c = 1.258 g cm^-3. The structures determined by Patterson (I) and direct (II) methods were refined to R = 0.050 for 1330 reflections of I and R = 0.082 for 1012 reflections of II. The proper treatment of the positional disorder of the carbon atoms (C(5) and C(6)) forming the trans ring junction in I discovered two discrete conformations with a ratio of 1:2. The opposite chirality of atoms C(51) and C(52), and C(61) and C(62), indicates a simultaneous configurational disorder with a pattern of total disorder: A A . The puckering parameters of the hetero rings in the same enantiomers of molecules IA, IB and II indicate a connection between the conformers: ⁵E(II)→⁵H₆(IB)→E₆IA) via pseudorotation. Their relationship is discussed and compared with the conformational freedom of the analogous 1,3-oxazine derivatives.     

Cis- and trans-3-hexene: infrared spectrum in liquid argon solution, ab initio calculations of equilibrium geometry, normal coordinate analysis, and vibrational assignments

The infrared spectra of cis-3-hexene and trans-3-hexene dissolved in liquid argon have been obtained at temperatures from 93 to 120 K. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. Ab initio molecular orbital calculations were performed to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using 6-31G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates. The scale factors of ab initio calculated force fields were determined. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Vibrational normal modes calculated for the lowest energy rotamers of cis- and trans-3-hexene have been assigned to infrared absorption bands observed in liquid argon solution. The assignments were based on calculated frequencies and potential energy distributions. The equilibrium geometries of the two lowest energy rotamers (symmetry C₂ and C_s) of cis-3-hexene and of the three lowest energy rotamers (symmetry C_i, C₂, and C₁) of trans-3-hexene were calculated. Variable temperature studies of the infrared spectrum of cis- and trans-3-hexenes dissolved in liquid argon were done to obtain the ΔH of conversion between the rotamers C₂ and C_s of cis-3-hexene and between the rotamers C_i, C₂, and C₁ of trans-3-hexene.     

Kinetic study of trifluoromethylation with s-(trifluoromethyl) dibenzothiophenium salts

The kinetic parameters were determined for C-trifluoromethylation of aniline with S-(trifluoromethyl)dibenzothiophenium triflate (1), its 3,7-dinitro derivative (2) and S-(trifluoromethyl)diphenylsulfonium triflate (3) in DMF-d₇. The higher reactivity of heterocyclic 1 compared with non-heterocyclic 3 could be explained on the basis of its greatly enhanced activation entropy (ΔS^≠: −11.2 cal mol ⁻¹ K⁻¹ for 1; −47.1 for 3), but not its enhanced activation enthalpy (ΔH^≠: 21.2 kcal mol⁻¹ for 1; 12.1 for 3). The aromatic delocalization of the heterocyclic ring may thus be only slightly disturbed by the S-trifluoromethyl substituent. The high reactivity of 2 was attributed to the great electron deficiency caused by two nitro groups in addition to the heterocyclic salt system (ΔH^≠ 17.0 kcal mol⁻¹, ΔS^≠ −9.1 cal mol⁻¹ K⁻¹ for 2). The reaction mechanism is discussed; the conventional S_N2 attack mechanism was ruled out and a mechanism for a side-on attack to the CF₃-S bond may possibly be applicable.     

Zur Komplexierung von enantiomerenreinen cis- und trans-3-Diphenylphosphino-4-hydroxy-tetrahydrofuranen mit [Rh(COD)2]BF4

The complexation behaviour of cis- und trans-3-diphenylphosphino-4-hydroxyl-tetrahydrofurans with [Rh(COD)₂]BF₄ is studied with the help of NMR and IR spectroscopy. In dependence of the spatial arrangement of hydroxyl and phosphino group the formation of different intra- and intermolecular bridged O-P complexes has been observed.

Zusammenfassung

Das Komplexierungsverhalten von cis- und trans-3-Diphenylphosphino-4-hydroxy-tetrahydrofuranen mit [Rh(COD)₂]BF₄ wird mit Hilfe von NMR- und IR-Spektroskopie studiert. In Abhängigkeit von der räumlichen Anordnung von Hydroxy- und Phosphinogruppe zueinander wird die Bildung von intra- bzw. intermolekular verbrückten O-P-Komplexen beobachtet.     

Synthesis of mer-[RuCl3(DMSO)(bpy)], reactivity and electrochemistry of mer-[RuCl3(DMSO)(bpy)] and mer-[RuCl3(TMSO)(bpy)] complexes

[H(DMSO)₂][trans-RuCl₄(DMSO)₂] (1) reacts with 2,2′-bipyridine in ethanol at room temperature resulting in the formation of a major compound, mer-[RuCl₃(DMSO)(bpy)] (bpy = 2,2′-bipyridine) 3 and a known minor compound, cis-[RuCl₂(DMSO)₄] (4). The compounds 3 and 4 are formed via an anticipated intermediate mer-[RuCl₃(DMSO)₃] (2). The reaction of 3 and mer-[RuCl₃(TMSO)(bpy)] (5) with small molecules like imidazole, carbon monoxide and KSCN yield, mer-[RuCl₃(bpy)(im)] · 2DMSO (im = imidazole) (6) and cis-[RuCl₂(TMSO)(CO)(bpy)] (7), cis-[RuCl₂(DMSO)(CO)(bpy)] (8) and K[RuCl₃(bpy)(SCN)] (9), respectively. The formations of 3, 6 and 7 have been authenticated by single crystal structure determinations. Compound 6 is formed by the substitution of DMSO or TMSO from 3 and 5, respectively, whereas 7 and 8 are formed by unprecedented one-electron reductions of 5 and 3. The reactions of 3 and 5 with KSCN resulted in the same compound, K[RuCl₃(NCS)(bpy)] (9). DFT calculations were performed to distinguish whether the thiocyanate ligand is bound to ruthenium through S or N. In the ruthenium bipyridine systems, the HOMO contains ruthenium d-orbitals and the LUMO is typically π^*-orbitals of the bipyridine ring. Complexes 3, 6 and 7 are redox active in acetone and DMSO solvent showing prominent a reduction peak and corresponding oxidation peak.     

Fluorocyclohexanes-II Cis- and trans- 1H:3H- and 1H:4H-decafluorocyclohexanes

An extension of the methods employed in the isolation of (trans) 1H/2H-decafluorocyclohexane,¹ (I) from the polyfluorocyclohexane mixture obtained by the vapour phase fluorination of benzene with cobaltic fluoride at about 150°, has afforded the four remaining members of the series of decafluorocyclohexanes [the cis- and trans-1H:3H- and 1H:4H-isomers (1H:3H/-(IV), 1H/3H-(III), 1H:4H/-(VII), and 1H/4H-(VIII), respectively)] and also the cis-1H:2H-decafluorocyclohexane (II), obtained previously^1,2 by the lithium aluminium hydride reduction of 1:2-dichlorodecafluorocyclohexane. The structures of the 1H:3H- and 1H:4H-decafluorides have been established by dehydrofluorination studies. The six decafluorocyclohexanes have been related to two new nonafluorocyclohexanes³ (IX and X) by further fluorination of the latter. 2H-Heptafluoroadipic acid has been obtained from 3H-nonafluorocyclohex-1-ene (V), one of the dehydrofluorination products of the 1H:3H-decafluorides.     

Practical synthesis of L-erythro- and L-threo-4-fluoroglutamic acids using aminoacylase

Enantiomerically pure L-erythro- and L-threo-4-fluoroglutamic acids 1a and 1b were conveniently prepared. The key steps in this synthesis relied upon separation of diastereomers of N-chloroacetyl-4-fluoroglutamic acid 5-methyl ester 7 by recrystallization and enzymatic resolution of enantiomers of the resulting 7(a+c) and 7(b+d) by aminoacylase. Protection of the γ-carboxyl group as a methyl ester was found to be crucial for this enzymatic reaction.     

Stereochemical non-rigidity of N-(dimethylhalogenosilylmethyl)-N-(1-phenylethyl) acetamides in solutions

The structure and dynamic behavior of (O-Si)-chelate N-(dimethylhalogenosilyl)methyl acetamides of the type MeC(O)N(CH(Ph)Me)CH₂ SiMe₂ X, where X = F, Cl, Br with the OSiC₃X coordination set, were studied by multinuclear (¹H, ¹³C, ¹⁷O, ²⁹Si) and dynamic ¹H NMR spectroscopy. Ligand permutation at silicon was detected. The observed influence of the solvent, nucleofugacity of the X substituent and the external nucleophile on the calculated values of the free energies of activation testify to the dissociative and/or associative mechanisms of the process, but including the stages in which the regular (pseudo-rotation or ‘turnstile’) mechanism takes place. At lower temperatures (up to −90°C) the ¹H, ¹³C, ²⁹Si NMR spectra of N-(dimethylchlorosilyl)methyl acetamide contain the signals of two species of unequal intensity. This effect was explained by an equilibrium between monomers containing the intramolecular O → Si bond and dimers with a hexacoordinate silicon and the bridging chlorine atoms.     

Synthesis and X-ray crystal structures of rac- and meso-2,2′-propylidene-bis(1-indenyl) zirconium dichlorides

An improved synthesis of 2,2′-bis(1-indenyl)propane and the corresponding ansa-complexes of zirconium are reported. Synthesis of a mixture of rac- and meso-2,2′-propylidene-bis(1-indenyl)zirconium dichlorides involves a treatment of ZrCl₄ with bis[3-(trialkyltin)inden-1-yl]propane, where alkyl = ethyl, butyl, in toluene. This reaction gives the products in 92% yield and might be a convenient synthetic pathway to a number of straightforward ansa-metallocenes. Both rac- and meso-2,2′-propylidene-bis(1-indenyl)zirconium dichlorides were separated and isolated using simple work-up processes, and characterized by X-ray crystal structure analysis (rac:C2/c; a = 15.903(3) Å, b = 11.105(2) Å and c = 11.520(2) Å; β = 121.61(3)°; Z = 4; V = 1732.6(5) ų; R = 0.0350; meso-: P1¯; a = 9.739(2) Å, b = 12.798(4) Å and c = 15.322(4) Å; = 101.18(2)°; β = 121.61(2)°; γ = 90.54(2)°, Z = 4; V = 1795.4(8) ų; R = 0.0417).     

Studies in the pinacol rearrangement—V The rearrangements of cis- and trans-1,2-diphenyl-1,2-ditolylethylene oxides

The intermediate formation of the two epoxides was observed in the perchloric acid-catalysed rearrangement of meso-2,2′-dimethylbenzpinacol (P_meso) to 2-methylbenzoyl tolyl diphenyl methane (K) Two kinds of epoxides were separated with preparative TLC and the configuration (cis and trans) of these epoxides was inferred in the light of UV, NMR and IR spectra, dipole moment and kinetic data. The rearrangement rates of these epoxides were measured in HClO₄-anhydrous acetic acid. Linear correlations of logarithm of the rate constants (log k) with the Hammett acidity function of the medium (H₀) were obtained, which supports the A-1 mechanism, together with the large positive values of the entropy of activation. It is shown that the perchloric acid-catalysed rearrangement of meso-2,2′-dimethylbenzpinacol (P_meso) occurs via such many kinetically distinguishable routes as the following where C and T are cis- and trans-epoxide respectively. The mechanisms of the rearrangements were discussed from the data of kinetics.     

E-2-Benzylidenebenzocycloalkanones. IV. Studies on transmission of substituent effects on C NMR chemical shifts of E-2-(X-benzylidene)-1-tetralones, and -benzosuberones. Comparison with the C NMR data of chalcones and E-2-(X-benzylidene)-1-indanones

Single substituent parameter (SSP) and dual substituent parameter (DSP) analyses were applied to study the transmission of substituent effects on selected ¹³C NMR chemical shifts of the cyclic chalcone analogues, E-2-(4′-X-benzylidene)-1-tetralones (2) and E-2-(4′-X-benzylidene)-1-benzosuberones (3). In order to study how the geometry of the cyclic chalcone analogues affects the transmission of substituent effects similar investigations with the respective chalcones (4) were also performed. The results obtained earlier with the five-membered analogue E-2-(4′-X-benzylidene)-1-indanones (1) were also involved in the comparisons. Geometry optimization of the unsubstituted 1a, 2a, 3a and 4a as well as the substituted 2 and 3 was performed by ab initio quantum chemical calculations. Both SSP and DSP analyses reflected that resonance effects contribute more to the chemical shift of C- (C2), while inductive effects primarily affect that of C-β (C10) of the enone moiety of all the four series. This latter effect, however, is far not as pronounced as that of the former one. It was found that DSP analysis data (ρ_F and ρ_R values) of transmission of substituent effects on the δC2 data can serve as a measure of choice to study the conformation (planarity) of the investigated enones in the four series.     

Interaction in trans-2-halocyclohexanols — an infrared and theoretical study

The O–H and C–O stretching frequencies of trans-2-halocyclohexanols in CCl₄ solutions have been measured and theoretical calculations have been performed to elucidate the main interactions, which are responsible for the conformational equilibria in these systems. It can be concluded that hydrogen bonding is predominant for trans-2-fluorocyclohexanol, leading to a stabilization of the eq–eq conformation, while for the chlorine, bromine and iodine derivatives, besides hydrogen bonding, gauche and steric interactions are also present.     

Structural, spectral and thermal studies of N-2-(4-picolyl)- and N-2-(6-picolyl)-N′-(2-chlorophenyl)thioureas and N-2-(6-picolyl)-N′-(2-bromophenyl)thiourea

N-2-(4-picolyl)-N′-2-chlorophenylthiourea, 4PicTu2Cl, monoclinic, P2₁/c, a=10.068(5), b=11.715(2), β=96.88(4)°, and Z=4; N-2-(6-picolyl)-N′-2-chlorophenylthiourea, 6PicTu2Cl, triclinic, P-1, a=7.4250(8), b=7.5690(16), c=12.664(3) Å, =105.706(17), β=103.181(13), γ=90.063(13)°, V=665.6(2) ų and Z=2 and N-2-(6-picolyl)-N′-2-bromophenylthiourea, 6PicTu2Br, triclinic, P-1, a=7.512(4), b=7.535(6), c=12.575(4) Å, a=103.14(3), β=105.67(3), γ=90.28(4)°, V=665.7(2) ų and Z=2. The intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen, as well as the planarity of the molecules, are affected by the position of the methyl substituent on the pyridine ring. The enthalpies of fusion and melting points of these thioureas are also affected. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in their spectra.     

Structural and spectral studies of N-2-(pyridyl)-, N-2-(3-, 4-, 5-, and 6-picolyl)- and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenylthioureas

Structures of the following compounds have been obtained: N-(2-pyridyl)-N′-2-thiomethoxyphenylthiourea, PyTu2SMe, monoclinic, P2₁/c, a=11.905(3), b=4.7660(8), c=23,532(6) Å, β=95.993(8)°, V=1327.9(5) ų and Z=4; N-2-(3-picolyl)-N′-2-thiomethoxyphenyl-thiourea, 3PicTu2SeMe, monoclinic, C2/c, a=22.870(5), b=7.564(1), c=16.941(4) Å, β=98.300(6)°, V=2899.9(9) ų and Z=8; N-2-(4-picolyl)-N′-2-thiomethoxyphenylthiourea, 4PicTu2SMe, monoclinic P2₁/a, a=9.44(5), b=18.18(7), c=8.376(12) Å, β=91.62(5)°, V=1437(1) ų and Z=4; N-2-(5-picolyl)-N′-2-thiomethoxyphenylthiourea, 5PicTu2SMe, monoclinic, C2/c, a=21.807(2), b=7.5940(9), c=17.500(2) Å, β=93.267(6)°, V=2893.3(5) ų and Z=8; N-2-(6-picolyl)-N′-2-thiomethoxyphenylthiourea, 6PicTu2SMe, monoclinic, P2₁/c, a=8.499(4), b=7.819(2), c=22.291(8) Å, β=90.73(3)°, V=1481.2(9) ų and Z=4 and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenyl-thiourea, 4,6LutTu2SMe, monoclinic, P2₁/c, a=11.621(1), b=9.324(1), c=14.604(1) Å, β=96.378(4)°, V=1572.4(2) ų and Z=4. Comparisons with other N-2-pyridyl-N′-arylthioureas having substituents in the 2-position of the aryl ring are included.     

Asymmetric Desymmetrization of Saturated and Unsaturated meso-1,2-Diols

An asymmetric desymmetrization of saturated and unsaturated cyclic and acyclic meso-1,2-diols has been developed from the ene acetals, prepared from the norbornene carboxyaldehyde and meso-1,2-diols. The intramolecular haloetherification of the ene acetals as a key step afforded 8-membered acetals in a stereoselective manner just by the reaction of norbornene olefin even when the ene acetals from unsaturated meso-1,2-diols having olefins in the same molecule were used. Subsequent reductive elimination, followed by protecting the hydroxy group and transacetalization, gave optically active 1,2-diol derivatives and the starting ene acetals in good yields.     

Regioselective 2H-3,6-dihydropyran synthesis with tandem oxo-ene formalism

Condensation of 3-alkenamides with s-trioxane in the presence of trifluoromethanesulfonic acid affords 2H-3,6-dihydropyrans.     

Vapour–liquid equilibrium for the ethyl ethanoate + 1-butene, +cis-2-butene, +trans-2-butene, +2-methylpropene, +n-butane and +2-methylpropane

Isothermal vapour–liquid equilibrium was measured for ethyl ethanoate + 1-butene, +cis-2-butene, +trans-2-butene, +2-methylpropene, +n-butane and +2-methylpropane at 318.4 K with an automated static total pressure measurement apparatus. The experimental data was correlated with the Wilson activity coefficient model. A good agreement between the experiments and the model was achieved. All six binary systems exhibited positive deviation from Raoult's law.     

A one-pot synthesis of functionalized 2,2-disubstituted 2H-1-benzopyrans

The synthesis of functionalized 2,2-disubstituted 2H-1-benzopyrans was achieved by condensing 2,3,5-trimethylhydroquinone (TMHQ) with ,β-unsaturated aldehydes or ,β-unsaturated acetals under acidic conditions.