(2,2-Dimethyl-2H-benzimidazol)-kupfer(I)-perchlorat-Komplexverbindungen

(2,2-Dimethyl-2H-benzimidazole)-copper (I) Perchlorate Complexes Reaction of bis(o-phenylenediamine)copper(II) perchlorate with acetone yields (2,2-dimethyl-2H-benzimidazole)-copper(I) perchlorate 1 . This complex gives with aceto- and benzonitrile the deeply coloured compounds C₆H₄N₂C(CH₃)₂. CuClO₄ · 2 RCN (R = CH₃, C₆H₅). o-Phenylendiaminemonohydrochloride reacts with acetone to 2,2,4-trimethyl-1H-2,3-dihydrobenzo[b]1,4-diazepine-hydrochloride; KOH yields the free base 2 . The presence of 2,2-dimethyl-2H-benzimidazole in the primary Cu-complex and the structure of 2 are proved by ¹H- and ¹³C-NMR-spectra.     

Umsetzungen des Pentamethylcyclopentadienyl‐Halbsandwichkomplexes Cp*Ta(CO)4 mit Chlor,Brom und Iod

The reaction of Cp*Ta(CO)₄ ( 1 ) (Cp* = η⁵‐pentamethylcyclopentadienyl, η⁵‐C₅Me₅) with chlorine leads to Cp*TaCl₄ ( 2a ), whereas the corresponding reactions with bromine or iodine give the oxo‐bridged complexes [Cp*TaX₃]₂(μ‐O) (X = Br ( 3b ), I ( 3c )). The oxygen atom apparently stems from a carbonyl ligand. In the presence of air, the binuclear complexes 3a , b are converted into mononuclear Cp*Ta(O)X₂ ( 4b , c ). The X‐ray structural determination of [Cp*TaBr₃]₂(μ‐O) ( 3b ) confirms a linear Ta–O–Ta bridge with a Ta–O distance of 190,4(1) pm.     

Synthesis and characterization of new bis(crown ether)s of Schiff base type containing recognition sites for sodium and nickel guest cations

New bis(crown ether) ligands of Schiff base type ( 2 – 4 ) containing recognition sites for sodium and nickel guest cations have been synthesized by the condensation of two equivalents of 4′-formyl-5′-hydroxy(benzo-15-crown-5) ( 1 ) with diamines, H₂N–(CH₂)_n–NH₂(n = 2–4). Homonuclear ditopic crystalline 2 : 1 (Na⁺ : ligand) complexes ( 2a – 4a , 2b – 4b ) of the ligands with NaSCN and NaClO₄ have been prepared. The NaClO₄ complexes of 3 and 4 ( 3b and 4b ) form heteronuclear tritopic crystalline complexes with Ni²⁺ cations of stoichiometry 2 : 1 : 1 (Na⁺ : Ni²⁺ : ligand). A homonuclear monotopic Ni²⁺ complex has also been prepared by the reaction with Ni(CH₃COO)₂ · 6H_2O. The UV-VIS spectra of 2 – 4 and their NaClO₄ complexes ( 2b – 4b ) are studied in different solvents including acidic and basic media. In polar solvents, tautomeric equilibria (phenol–imine, O–H…︁N and ketoamine, O…︁H–N forms) are present, as supported by the UV-VIS data.     

Furanderivate. VII. 2-[Furyl-(2)- und 5-Nitro-furyl-(2)]vinylphosphonsäure-O,O-diethylester

Furanderivatives. VII. O,O-Diethyl-2-[furyl-(2)- and 5-nitro-furyl-(2)] vinylphosphonates Syntheses and spectroscopic properties (i.r., u.v., ¹H-, and ¹³C-n.m.r.) of the title compounds existing as E-isomers with the general structure 1–8 (R⁵  H, NO₂; R  CN, COOEt, H, NMe₂) are represented. According to spectroscopic data the compound 8 (R⁵  NO₂; R  NMe₂) differs in its electronic structure.     

Electropolymerization and characterization of terpyridinyl iron (II) and ruthenium (II) complexes

Electroactive 2,2′: 6,2″-terpyridinyl ligands ( 3, 5, 6 ) and their iron(II) ( 7a–9a ) and ruthenium(II) complexes ( 7b–9b ) were synthesized. Bis[3-(aminophenyl)-2,2′ :6,2″-terpyridinyl]metal(II) complexes ( 7a, 7b ) and bis[2-(hydroxyphenyl)-2,2′ :6,2″-terpyridinyl]metal(II) complexes ( 8a, 8b ) were electropolymerized on to the surface of Pt or In-SnO₂ (ITO) electrodes in acetonitrile containing Bu₄NCIO₄ by scanning the potential between O and + 1.6V (for 7a and 7b ), and ?0.8 and +1.6V (for 8a and 8b ) versus saturated calomel electrode. The electrodes obtained by electropolymerization exhibited reversible electrochromism based on Fe(II)/Fe(III) or Ru(II)/Ru(III) redox couple. Photoresponses to visible light were found in the modified electrode obtained by electropolymerization of ruthenium complex 7b in an aqueous LiClO₄ solution containing methylviologen (cation MV²⁺) under an O₂ atmosphere. The mechanism for the photoresponded cathodic current was explained in terms of an excitation of bis(terpyridinyl)ruthenium(II) complex [Ru(terpy)²₂⁺] by visible light, an electron transfer from the excited state [Ru(terpy)^2+*₂] to MV²⁺, reduction of Ru(terpy)³⁺₂ at an electrode, and oxidation of MV^+* with O₂.     

Photochemie und Photophysik von 3-(2-Isoxazolinyl)-phenylketonen

Photochemistry and Photophysics of 3-(2-Isoxazolinyl)-phenylketones 3-Benzoyl-Δ²-1,2-oxazolines ( 1–6 ) are formed by 1,3-dipolar cycloaddition between benzoylnitril-N-oxide ( 8 ) and dihydrofurane 9 or 1,3-dioxep-5-enes ( 10a–c ). The preparative yields are small due to the competitive dimerization of the dipole 8 . Two stereoisomers are obtained by using 2-substituted 1,3-dioxep-5-enes as dipolarophiles. The different steric position of the substituents in 3–6 gives rise to different spectral data. The synthesized ketones possess triplet states with a high degree of charge transfer character. Therefore, the ability to H-abstraction reaction from alcohols is small. For ketone 2 and methanol as H-donor a rate constant of k = 4,1 · 10² M⁻¹s⁻¹ is determined. Also by electron transfer reactions with triethylamine and some onium compounds the reactivity of the T₁ of the ketones 1–6 is less compared to those of nπ* excited ketones. The photolysis of the ketones takes place very unselectively and leads to a product mixture. The quantum yields for the decay of the ketones are 10⁻² to 10⁻³.     

Die Reaktion von E-ß-Nitro-styrolen mit Pyrazolidon-(3)-azomethiniminen – eine nicht-cisoide 1,3-dipolare Cycloaddition

The Reaction of E-ß-Nitro-styrenes with 3-Pyrazolidone-azomethinimines – a Non-cisoid 1,3-Dipolar Cycloaddition Normal flipping at both ring-N-atoms postulated, the thermal addition of E-β-nitro- 5a or E-(4-chloro-β-nitro)-styrene 5b to 3-pyrazolidone-azomethinimine-1,3-dipoles 4a or 4b formally can yield 8 isomeric pairs of enantiomers, 4 of which are “permitted”(cisoid) and 4 of which are “forbidden” according to the concerted [_π4_s + _π2_s]-mechanism. If the addition of 5 to 4 is regiospecific, 2 “permitted”(cisoid) ( 1 and 6 ) and 2 “forbidden”( 3 and 10 ) isomers are conceivable. From pure 5a and 4a we regiospecifically got 1ref,3trans-diphenyl-2cis-nitro- 6a (75%) and 1ref,3trans-diphenyl-2trans-nitro-5-oxo-perhydropyrazolo[1,2-a]pyrazol 10a (25%), from 5b and 4b the corresponding bis(4-chloro-phenyl)-isomers 6b and 10b . The sodium salts 8a, b , gained from 6a, b and 10a, b , are identical. With H⊕ (D⊕) in water (D₂O) 8a, b give 6a, b (2-deutero- 6a, b = 7 a, b ). The ¹H-n.m.r. spectra of 6a, b, 7a, b, 8a, b, 10a, b , and of the 2-amino-isomers 11a/12a , corresponding to 6a/10a , are discussed. For the first time products of a non-cisoid 1,3-dipolar cycloaddition ( 10a, b ) were isolated. In the discussion (E ⇌ Z)-isomerization of 5a , and conceivable mechanisms of isomerizations 6a → 10a are excluded. Theoretical consequences are suggested.     

A novel Wells–Dawson polyoxometalate-based metal–organic framework constructed from the uncommon in-situ transformed bi(triazole) ligand and azo anion

A novel Wells–Dawson polyoxometalate (POM)-based metal–organic framework (MOF) constructed from bi(triazole) ligand and azo anion, namely, [Ag₁₃(L)₆(N₂)(HP₂W₁₈O₆₂)] (1) (HL = 4-(1 H-1,2,4-triazol-3-yl)-2 H-1,2,4-triazolyl) has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, IR spectra, PXRD analysis. In compound 1, the rigid bi(triazole) ligands connected Ag^I ions to construct a 2D metal–organic layer, which was further extended by azo anions forming a 3D framework. The Wells–Dawson type [P₂W₁₈O₆₂]^6 − anion as a multidentate inorganic ligand coordinated with the Ag^I ions, consolidating the 3D MOF. The L ligands and azo anions were in-situ transformed from a bi(triazole) derivative, which has never been observed in previous reports. In addition, the electrocatalytic and photocatalytic properties of compound 1 have been investigated.     

Metal–Fluorocarbon Pyrolants: X. Influence of Ferric Oxide/Silicon Additive on Burn Rate and Radiometric Performance of Magnesium/Teflon/Viton® (MTV)

Both burn rate, u (mm s⁻¹) and mass consumption rate, (g s⁻¹ cm⁻²) of fuel rich magnesium/Teflon/Viton^® (MTV) (45/50/5) upon addition of silicon/ferric oxide for part of the PTFE decrease by 16 and 11%, respectively. However, the spectral efficiency E_β (J g⁻¹ sr⁻¹) increases by 24% in the 3–5 μm band.     

On the Reaction of α,α-Dichlorocarbenium Ions with Isocyanates

Trichlormethanes 4 react with two equivalents of n-alkyl isocyanates R²-NCO in the presence of SbCl₅ to furnish the 2,2-dichloro-5,6-dihydro-6-oxo2H-1,3,5-oxadiazinium salts ( 9 ). The structure of these heterocycles is confirmed by an X-ray analysis of 9d (R¹ = ClC = CCl₂, R² = Et). p-Tolyl isocyanate is Friedel-Crafts alkylated by 4b in the presence of SbCl₅. Subsequent ring closure affords the quinolinium salt 13 , which is hydrolyzed to give inter alia the quinolone 16 .     

Synthesis and properties of novel poly(meth)‐acrylates containing tricyanocyclopropyl groups for piezoelectric applications

o‐(2,2,3‐Tricyano‐3‐carbomethoxycyclopropyl)phenoxyethyl acrylate ( 5a ) and o‐(2,2,3‐tricyano‐3‐carbomethoxycyclopropyl)phenoxyethyl methacrylate ( 5b ) were prepared by reactions of bromomalononitrile with methyl o‐(2‐acryloyloxyethoxy)benzylidenecyanoacetate and methyl o‐(2‐methacryloyloxyethoxy)benzylidenecyanoacetate respectively. The dipole moments of 5a and 5b , calculated by atom superposition and electron delocalization molecular orbital method, were 2.75–3.47 D. Monomers 5a and 5b were polymerized with free‐radical initiators to obtain the polymers with tricyanocyclopropane ring as a piezoelectric chromophore in the pendant group. The resulting polymers 6a and 6b were soluble in common organic solvents such as acetone and DMF. Polymers 6a and b showed thermal stability up to 280 °C in TGA thermograms. T_g values obtained from DSC thermograms were in the range 125–140 °C. Piezoelectric coefficients (d₃₁) of the poled films were 1.2–1.4 pC N^?1. These polymers showed good temporal and long‐term thermal stabilities which are acceptable for piezoelectric device applications. Copyright © 2003 Society of Chemical Industry     

Facile Hydrogenolysis of C(sp3)–C(sp3) σ Bonds

The modification of benzylic quaternary, tertiary, and secondary carbon centers through palladium‐catalyzed hydrogenolysis of C(sp³)–C(sp³) σ bonds is presented. When benzyl Meldrum's acid derivatives bearing quaternary benzylic centers are treated under mild hydrogenolysis conditions – palladium on carbon and atmospheric pressure of hydrogen – aromatics substituted with tertiary benzylic centers and Meldrum's acid are obtained with good to excellent yield. Analogously, substrates containing tertiary or secondary benzylic centers yield aromatics substituted with secondary benzylic centers or toluene derivatives, respectively. Furthermore, this strategy is used for the high yielding synthesis of diarylmethanes. The scope of the reductive dealkylation reaction is explored and the limitations with respect to steric and electronic factors are determined. A mechanistic analysis of the reaction is described that consisted of deuterium labelling experiments and hydrogenolysis of enantioenriched derivatives. The investigation shows that the C(sp³)–C(sp³) σ bond‐cleaving events occur through a hybrid S_N1/S_N2 mechanism, in which the palladium center displaces a carbon‐based leaving group, namely Meldrum's acid, with inversion of configuration, followed by reductive elimination of palladium to furnish a C−H bond.

     

Thermolytic conversion of a bis(alkoxy)tris(siloxy)tantalum(V) single-source molecular precursor to catalytic tantala–silica materials

The new complex (ⁱPrO)₂Ta[OSi(O ^tBu)₃]₃ (1) was prepared via silanolysis of Ta(O ⁱPr)₅ with (^tBuO)₃SiOH and is a useful structural and spectroscopic (NMR, FTIR) model of Ta(V) on silica. The complex was also used to prepare tantalum-containing silica materials, via the thermolytic molecular precursor method (yielding Ta₂O₅ ⋅ 6SiO₂ and Ta₂O₅ ⋅ 18SiO₂) or by grafting 1 onto mesoporous SBA-15 silica (yielding a surface-supported tantala species, TaSBA-15). The solution phase thermolysis of 1 in nonpolar media afforded homogeneous, high-surface-area (ca. 450 m² g⁻¹) xerogels (Ta₂O₅ ⋅ 6SiO₂) that are amorphous up to approximately 1100 °C. A more silica-rich tantala–silica material (Ta₂O₅ ⋅ 18SiO₂) was prepared via a solution-phase co-thermolytic route with 1 and HOSi(O ^tBu)₃, to yield a material with a Si/Ta ratio of 9/1. It was demonstrated that tantala–silica materials are active as catalysts for cyclohexene oxidation.     

Non‐isothermal crystallization behavior of stereo diblock polylactides with relatively short poly(d‐lactide) segments from the melt

Stereo diblock polylactides (SDB‐PLAs) composed of relatively short poly(d ‐lactide) (PDLA) segments and relatively long poly(l ‐lactide) (PLLA) segments were synthesized to have a wide number‐average molecular weight (M_n) range of 2.5 × 10⁴–2.0 × 10⁵ g mol^?1 and d ‐lactyl unit content of 0.9–38.6%. The effects of incorporated short PDLA segments (M_n = 2.0 × 10³–7.7 × 10³ g mol^?1) on crystallization behavior of the SDB‐PLAs were first investigated during heating after complete melting and quenching or during slow cooling after complete melting. Stereocomplex (SC) crystallites can be formed at d ‐lactyl unit content as low as 4.3 and 5.8% for heating and slow cooling, respectively, and for M_n of PDLA segments as low as 2.0 × 10³ and 3.5 × 10³ g mol^?1, respectively. With decreasing M_n and increasing d ‐lactyl unit content, the cold crystallization temperature during heating decreased and the crystallization temperature during slow cooling increased. With increasing d ‐lactyl unit content, the melting enthalpy (ΔH_m) of SC crystallites during heating and the crystallinity (X_c) of SC crystallites after slow cooling increased, whereas ΔH_m of PLLA homo‐crystallites during heating and X_c of PLLA homo‐crystallites after slow cooling decreased. The total ΔH_m of SC crystallites and PLLA homo‐crystallites during heating and the total X_c after slow cooling became a minimum at d ‐lactyl unit content of 10–15% and gave a maximum at d ‐lactyl unit content of 0%. Despite the accelerated crystallization of some of SDB‐PLAs, the low values of total ΔH_m and X_c at d ‐lactyl unit content of 10–15% are attributable to the formation of two crystalline species of SC crystallites and PLLA homo‐crystallites.     

Oxidative Hydrophenylation of Ethylene Using a Cationic Ru(II) Catalyst: Styrene Production with Ethylene as the Oxidant

The complex [(MeOTTM)Ru(P(OCH₂)₃CEt)(NCMe)Ph][BAr′₄] (MeOTMM=4,4’,4’’-(methoxymethanetriyl)-tris(1-benzyl-1H-1,2,3-triazole), BAr′₄=tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) is used to catalyze the hydrophenylation of ethylene to produce styrene and ethylbenzene. The selectivity of styrene versus ethylbenzene varies as a function of ethylene pressure, and replacing the MeOTTM ligand with tris(1-phenyl-1H-1,2,3-triazol-4-yl)methanol reduces the selectivity toward styrene. For styrene production ethylene serves as the oxidant to produce ethane, as determined by both ¹H NMR spectroscopy and GC-MS. The Ru(III/II) potentials of [(MeOTTM)Ru[P(OCH₂)₃CEt](NCMe)Ph][BAr′₄] (0.86 V) and [(HC(pz⁵)₃)Ru[P(OCH₂)₃CEt](NCMe)Ph][BAr′₄] (0.82 V) (HC(pz⁵)₃=tris(5-methyl-pyrazolyl)methane) are nearly identical. Since catalytic conversion of ethylene and benzene by [(HC(pz⁵)₃)Ru[P(OCH₂)₃CEt](NCMe)Ph][BAr′₄] is known to selectively produce ethylbenzene, the formation of styrene using [(MeOTTM)Ru[P(OCH₂)₃CEt](NCMe)Ph][BAr′₄] is attributed to the substituents on the triazole rings of the MeOTTM ligand.     

A unique diruthenium(II,III) unit surrounded by tridentate ligands of N-(2-pyridyl)-2-oxy-5-chlorobenzylaminate

A new metal–metal bonded diruthenium(II, III) compound with a dianionic tridentate ligand, N-(2-pyridyl)-2-oxy-5-chlorobenzylaminate (5-Clsalpy²⁻), was synthesized and structurally characterized as Li₂(THF)₄Cl[Ru₂(5-Clsalpy)₃] (1). The 5-Clsalpy²⁻ ligand that acts as a bridging/chelating co-ligand afforded a unique coordination mode of [M–M bridging/equatorial-chelating] in addition to the “common” mode of [M–M bridging/axial-chelating] around the diruthenium unit of 1.     

Application of poly(phthalazinone ether sulfone ketone)s to gas membrane separation

A series of poly(phthalazinone ether sulfone ketone) (PPESK) copolymers containing different component ratios of bis(4‐fluorodiphenyl) ketone and bis(4‐chlorodiphenyl)sulfone with respect to a certain amount of 4‐(4‐hydroxyphenyl)‐2,3‐phthalazin‐1‐one were synthesized by polycondensation. Glass transition temperatures of these polymers were adjusted from 263°C to 305°C by changing the ratios of reactants. Gas permeability and selectivity of the dense membranes of the polymers for three kinds of gases (CO₂, O₂, and N₂) were determined at different temperatures. The result indicated that the membrane of PPESK (S/K = 1/1, mol ratio) had an excellent gas separation property. Permeability of the polymer membranes for CO₂, O₂, and N₂ was P = 4.121 barrier, P = 0.674 barrier, and P = 0.0891 barrier, respectively. Separation factors of α and α were 7.6 and 46, respectively. New material was made into a composite membrane with silicone rubber for blocking up leaks and defects on the surface of its nonsymmetrical membrane. As a result of the test, permeability of the composite membrane was J = 7.2 × 10⁻⁶ cm³ (STP) cm⁻² S⁻¹ cm⁻¹ Hg and J = 0.99 × 10⁻⁶ cm³ (STP) cm⁻² S⁻¹ cm⁻¹ Hg, whereas the α was still higher than 7. These showed that PPESKs had a bright prospect as the potential membrane material for high‐temperature gas separation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2385–2390, 1999     

2,5-Dialkoxysubstituierte Oligo- und Poly(1,4-phenylenethenylen)e

2,5-Dialkoxy Substituted Oligo- and Poly(1,4-phenyleneethenylene)s O-Alkylation and regioselective Rieche formylation of 2-methylhydroquinone ( 1 ) yields the 2,5-dialkoxy-4-methylbenzaldehydes 4a–j . The corresponding azomethines 5a–j enter in a strongly alkaline medium a selfcondensation reaction leading to the title compounds 6/7a–j . These conjugated oligomers and polymers possess highly regular structures with exclusively (E)-configurated double bonds. GPC, IR, ¹H-, ¹³C-NMR and MS-FD measurements were used for their characterization. Somewhat different results were obtained for the similarly prepared Schiff base 5l which contains chlorine substituents in the side chains. Cleavage of hydrogen chloride leads not only to unsaturated alkoxy groups; additionally, cyclization reactions ( 5l → 8l ) are observed.     

Nickel(II) Coordination Polymers Supported by Bis-pyridyl-bis-amide and Angular Dicarboxylate Ligands: Role of Ligand Flexibility in Iodine Adsorption

Reactions of N‚N’-bis(3-pyridylmethyl)oxalamide (L¹), N‚N’-bis(4-pyridylmethyl)oxalamide (L²), or N,N’-bis(3-pyridylmethyl)adipoamide) (L³) with angular dicarboxylic acids and Ni(II) salts under hydro(solvo)thermal conditions afforded a series of coordination polymers: {[Ni(L¹)(OBA)(H₂O)]·H₂O}_n (H₂OBA = 4,4-oxydibenzoic acid), 1, {[Ni(L¹)(SDA)(H₂O)₂]·H₂O·CH₃OH}_n (H₂SDA = 4,4-sulfonyldibenzoic acid), 2, {[Ni(L²)(OBA)]·C₂H₅OH}_n, 3, {[Ni(L²)(OBA)]·CH₃OH}_n, 4, {[Ni₂(L²)(SDA)₂(H₂O)₃]·5H₂O}_n, 5, {[Ni₂(L²)(SDA)₂(H₂O)₃]·H₂O·2C₂H₅OH}_n, 6, {[Ni(L³)(OBA)(H₂O)₂]·2H₂O}_n, 7, {[Ni(L³)(SDA)(H₂O)₂]·2H₂O}_n, 8, and {[Ni(L³)₀.₅(SDA)(H₂O)₂]·0.5C₂H₅OH}_n, 9, which have been structurally characterized by using single-crystal X-ray crystallography. Complex 1 exhibits an interdigitated 2D layer with the 2,4L2 topology and 2 is a 2D layer with the sql topology, while 3 and 4 are 3D frameworks resulting from polycatenated 2D nets with the sql topology and 5 and 6 are 2-fold interpenetrated 3D frameworks with the dia topology. Complexes 7 and 8 are 1D looped chains and 9 is a 2D layer with the 3,4L13 topology. The various structural types in 1–9 indicate that the structural diversity is subject to the flexibility and donor atom position of the neutral spacer ligands and the identity of the angular dicarboxylate ligands, while the role of the solvent is uncertain. The iodine adsorption of 1–9 was also investigated, demonstrating that that the flexibility of the spacer L¹–L³ ligands can be an important factor that governs the feasibility of the iodine adsorption. Moreover, complex 9 shows a better iodine adsorption and encapsulates 166.55 mg g⁻¹ iodine in the vapor phase at 60 °C, which corresponded to 0.38 molecules of iodine per formula unit.     

Synthese und Reaktionen chiraler,von (R)-(−)-bzw. (S)-(+)-2-Methoxymethylpyrrolidin abgeleiteter Dithiocarbamate

Synthesis and Reactions of Chiral Dithiocarbamates Derived from (R)-(−)- or (S)-(+)-2- The synthesis, diastereoselective alkylation reactions, dithiocarboxylation, and aldol condensation of several substituted methyl (R¹ CH₂) (S)-2-(methoxymethyl)-pyrrolidine-1-dithiocarboxylates (S)- 2 and of the corresponding (R)-derivatives (R)- 2 are described. The new enantiomeric dithiocarbamates (S) -2a – e , and (R) -2a – d are obtained by reaction of (S)-(+)-[(S) -1 ] or (R)-(−)-2-(methoxymethyl)-pyrrolidine [(R) -1 ], respectively, with carbon disulfide in dry methanol/anhydrous sodium acetate and the appropriate alkylating agent. The cyclic ketene dithioacetals (S) -3 and (R) -3 are formed by dithiocarboxylation procedure of (S) -2a and (R) -2a whereas (S) -6 and (R) -6 are obtained by aldol reaction with isobutyraldehyde. (S)- 2c , d and (R) -2c , d react in a diastereoselective manner after deprotonation with n-BuLi or LiTMP/LiBr at −78°C in THF with alkyl halides to the enantiomeric compounds 4a /ent -4a, 4b /ent -4b and 5 /ent -5 , respectively.