Enantioselective synthesis of (1S,2S)-1,2-di-tert-butyl and (1R,2R)-1,2-di-(1-adamantyl)ethylenediamines

An enantioselective synthesis of sterically congested 1,2-di-tert-butyl and 1,2-di-(1-adamantyl)ethylenediamines has been developed. Thus, diastereomerically pure trans-1-apocamphanecarbonyl-4,5-dimethoxy-2-imidazolidinones 6 and 7 were successfully prepared by optical resolution of (±)-trans-4,5-dimethoxy-2-imidazolidinone using apocamphanecarbonyl chloride (MAC-Cl) followed by stereospecific and stepwise substitution of the dimethoxyl groups using tert-butyl or 1-adamantyl cuprates to provide (4S,5S)-4,5-di-tert-butyl and (4R,5R)-4,5-di-(1-adamantyl)-2-imidazolidinones 12 and 15, respectively. Furthermore, N-acetyl 4,5-di-tert-butyl and 4,5-di-(1-adamantyl)-2-imidazolidinones 16a,b were enantioselectively deacetylated using a catalytic oxazaborolidine system to provide enantiopure 1-p-tolylsulfonyl-4,5-di-tert-butyl-2-imidazolidinones 12 and 19 and 1-p-tolylsulfonyl-4,5-di-(1-adamantyl)-2-imidazolidinones 18 and 20, respectively. Finally, N-p-tolylsulfonyl-2-imidazolidinones 12 and 15 were treated with 30 equiv of Ba(OH)₂·8H₂O to achieve ring cleavage and to provide (1S,2S)-1,2-di-tert-butylethylenediamine 3 and (1R,2R)-1,2-di-(1-adamantyl)ethylenediamine 4.     

(R,R,R)-Tris(2-hydroxy-1-methylethyl)- and (S,S,S)-tris(2-hydroxy-2-methylethyl)phosphine: water-soluble chiral trialkylphosphines with C3-symmetry

The first α- and β-chiral water-soluble trialkylmonophosphines, 1 and 2, respectively, both with C₃ symmetry, were synthesised from sodium phosphide and chiral mesylates, accessible from (S)-ethyl lactate. X-ray structures of a corresponding 2:1 gold(I) complex [1₂Au(I)]OTf and of a borane complex 2·BH₃ were determined.     

Stereospecific preparation of symmetrical (1Z, 3Z)- and (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes from 1-bromo-1-fluoroalkenes

A straightforward method to prepare symmetrical (1Z, 3Z)- and (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes is described. High E/Z ratio 1-bromo-1-fluoroalkenes, prepared by isomerization from the E/Z ≈ 1:1 isomeric mixtures, reacted with Bu₃SnSnBu₃ and Pd(PPh₃)₄ to afford (1Z, 3Z)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes in good yield. (Z)-1-Bromo-1-fluoroalkenes, which were prepared by kinetic reduction from 1-bromo-1-fluoroalkenes (E/Z ≈ 1:1), can undergo similar reaction with Bu₃SnSnBu₃ and Pd(PPh₃)₄/CuI to prepare (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes.     

Ordered perovskites in the A(Li1/4Nb3/4)O3-A(Li2/5W3/5)O3 (A=Sr, Ca) systems

Single-phase 1:2 B-site ordered perovskites are formed in the (1−x)A²⁺(Li_1/4Nb_3/4)O₃-(x)A²⁺(Li_2/5W_3/5)O₃ systems, A²⁺=Sr and Ca, within the range 0.238?x?0.333. The X-ray and electron diffraction patterns are consistent with a P2₁/c monoclinic supercell, , , , β≈125°, where the 1:2 order is combined with b⁻b⁻c⁺ octahedral tilting. Rietveld refinements of the ordered A(B^I_1/3B^II_2/3)O₃ structures give a good fit to a model with B^I occupied by Li and Nb, B^II by W and Nb, and a general stoichiometry (Sr,Ca)(Li_3/4+y/2Nb_1/4−y/2)_1/3(Nb_1−yW_y)_2/3O₃, y=0.9x=0.21-0.30. The Sr system also includes regions of stability of a 1:3 ordered phase for 0.0?x?0.111, and a 1:1 ordered double perovskite for 0.833?x?1.0. The formation of the non-stoichiometric 1:2 ordered phases is associated with the large site charge/size differences that can be accessed in these systems, and restricted by local charge imbalances at the A-sites for W-rich compositions. These concepts are used to generate stability maps to rationalize the formation of the known 1:2 ordered oxide perovskites.     

Single-Crystal Growth and Classification of EuAlF5 and Solid Solutions M(II)1−xEuxAlF5 (M=Ca, Sr, Ba) within the Structural Family of Tetragonal M(II)M(III)F5 Compounds

The compound EuAlF₅, as well as the solid solutions Ca_0.19(1)Eu_0.81(1)AlF₅, Sr_0.15(1)Eu_0.85(1)AlF₅, Sr_0.55(1)Eu_0.45(1)AlF₅, Sr_0.77(1)Eu_0.23(1)AlF₅, and Ba_0.62(1)Eu_0.38(1)AlF₅, crystallize in colorless tetragonal columns. These have been prepared by solid state reactions at 900°C, starting from mixtures of the binary fluorides. According to Vegard's rule the solid solution Sr_1−xEu_xAlF₅ shows a linear dependence of the crystal volume on the molar ratio Eu/Sr. All crystal structures have been refined from single-crystal diffractometer data. EuAlF₅ and the M_1−xEu_xAlF₅ (M=Ca, Sr) compounds obtained are isotypic with β-SrAlF₅. They crystallize in a superstructure in space group I4₁/a (no. 88) with 64 formula units and lattice parameters a≈19.9 Å, c≈14.3 Å. The structure is characterized by chains of trans-corner-sharing [AlF_4/2F_2/1] and branched [AlF_5/1F_1/2] octahedra forming a channel structure. Inside the channels isolated ordered dimeric units [AlF_4/1F_2/2]₂ are located. The divalent metal atoms show coordination numbers 8 and 9; they connect the [AlF₆] octahedra into a three-dimensional structure. Ba_0.62(1)Eu_0.38(1)AlF₅ is isotypic with the corresponding Sr compound Ba_0.43(1)Sr_0.57(1)AlF₅, and it crystallizes with 16 formula units and lattice parameters a=14.3860(7) Å, c=7.2778(3) Å in space group I4/m (no. 87). The network structure is identical with that of EuAlF₅. Instead of the dimeric units, infinite chains [AlF_4/1F_2/2]_∞ of trans-corner-sharing [AlF₆] octahedra extending along the c- axis are located inside the channels. The bridging fluorine atoms of this chain show large anisotropic displacement parameters, but no superstructure reflections have been observed for this compound.     

Regiospecific synthesis of symmetrical (1E,3E) 2,3-difluoro-1,4-diphenyl-buta-1,3-dienes via palladium-catalyzed cross-coupling of (Z) 2-bromo-2-fluoroethenylbenzenes in presence of bis(pinacolato)diboron

The cross-coupling reaction of (Z) 1-bromo-1-fluoroalkenes catalyzed by PdCl₂(PPh₃)₂-2PPh₃ (3%) and CsF in Tetrahydrofuran (THF) in presence of bis(pinacolato)diboron led to (1E,3E) 2,3-difluoro-1,4-disubstituted-buta-1,3-dienes in high yields.     

Stereoselective synthesis of (1′S,3R,4R)-4-acetoxy-3-(2′-fluoro-1′-trimethylsilyloxyethyl)-2-azetidinone

A stereoselective synthesis of (1′S,3R,4R)-4-acetoxy-3-(2′-fluoro-1′-trimethylsilyloxyethyl)-2-azetidinone as a new fluorine-containing intermediate towards β-lactams, is described. The synthetic key step relies upon the dynamic kinetic resolution (DKR) of ethyl 2-benzamidomethyl-4-fluoro-3-oxo-butanoate via asymmetric transfer hydrogenation catalyzed by [Ru(η⁶-arene)(S,S)-R₂NSO₂DPEN].     

Isoquinolin-1(2H)-ones and 1,6-naphthyridin-5(6H)-ones by an N-acylation-SNAr sequence

A new synthesis of 2,3-dialkyl-4-carbomethoxyisoquinolin-1(2H)-ones and 6,7-dialkyl-8-carbomethoxy-1,6-naphthyridin-5(6H)-ones is reported. The process involves treatment of a β-enaminoester with 2-fluoro-5-nitrobenzoyl chloride, 2-fluorobenzoyl chloride or 2-chloronicotinoyl chloride followed by heating in the presence of base. The conversion, which proceeds by an N-acylation-S_NAr reaction sequence, affords 50–86% yields when R¹ is n-alkyl but ≤30% yields when R¹ is α-branched.     

Stereoselective synthesis of (E)-N,N-diethyl-3-(imidazo[1,2-a]pyrid-2-yl)-2-(phenylsulfonyl)propenamide

The title compound, gem-amidovinylsulfone 3, was synthesized stereoselectively by aldolic condensation of N,N-diethylphenylsulfonylacetamide 1 on imidazo[1,2-a]pyridine-2-carbaldehyde 2 adding Et₃N at the end. The X-ray crystal structure of 3 [C₂₀H₂₁N₃O₃S: M_r=383.5, monoclinic, P2₁, a=8.191(4) Å, b=21.132(2) Å, c=11.752(1) Å, β=96.40(2)°, V=2022(1) Å³, Z=4 (two molecules per asymmetric unit), D_calc=1.260 g cm⁻³, λ(Mo Kα)=0.71073 Å, μ=0.184 mm⁻¹, F(000)=808, T=293(2)K, R=0.059 for 5105 observed reflections with I≥2σ(I)] was determined, and confirmed the (E) configuration.     

Synthesis of (2S,3R)- and (2S,3S)-[3-H1]-proline via highly stereoselective hydrolysis of a silyl enol ether

A straightforward synthesis of (2S)-[3,3-²H₂]-proline 1c and (2S,3R)- and (2S,3S)-[3-²H₁]-proline, 1b and 1a, respectively, has been devised. The key step of the route to the latter compounds involves highly stereoselective hydrolysis of the silyl enol ethers 3 and 3a, respectively, with protonation (deuteriation) from the re-face of the silyl enol ether.     

Catalytic asymmetric synthesis of ethyl (1R,2S)-dehydrocoronamate

A synthesis of (1R,2S)-dehydrocoronamic acid ethyl ester was developed employing a regio- and enantioselective palladium-catalysed nucleophilic ring-opening of 3,4-epoxy-1-butene with a glycine anion equivalent as the key enantiodifferentiating step. The desired selectivity was achieved using Trost’s naphthyl ligand. The subsequent activation of the free hydroxyl group and ring-closure by intramolecular S_N2 reaction gave the desired amino acid ethyl ester.     

Synthesis of 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-ones via Pd-catalyzed regioselective cross-coupling reaction and cyclization

An efficient and novel route for the synthesis of 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-one 1 via palladium-catalyzed site-selective cross-coupling reaction and cyclization process was described. Reaction of 3-bromo-4-trifloxy-quinolin-2(1H)-one 3 with arylboronic acid catalyzed by PdCl₂(PPh₃)₂ afforded 3-bromo-4-aryl-quinolin-2(1H)-one 4, which then reacted with 2-ethynylaniline 5 via Pd-catalyzed Sonogashira coupling and CuI-mediated cyclization leading to the desired 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-one 1 in good yields.     

Stereoselective synthesis of (+)-(1R,2S,5S,7R)-2-hydroxy-exo-brevicomin

A stereoselective approach for the synthesis of (+)-(1R,2S,5S,7R)-2-hydroxy-exo-brevicomin from l-ascorbic acid has been described. The key steps are highly stereoselective nucleophilic addition reaction on aldehyde 8 and also a single pot transformation of 15 to (+)-(1R,2S,5S,7R)-2-hydroxy-exo-brevicomin. The later tandem reaction which involves the hydrogenation of double bond, debenzylation, MOM deprotection and bicyclic ketal formation was carried under Pd/C, H₂ followed by acid treatment.     

Practical synthesis of (E)- and (Z)-2-silyl-3-penten-1-ols with high enantiopurity

Practical methods for the synthesis of the optically active (E)- and (Z)-2-silyl-3-pentene-1-ols are described. The optically pure (E)-allylsilane was synthesized from commercially available (R)-3-butyn-2-ol in five steps involving hydrozirconation followed by alkylation of the resulting alkenylmetal with BnOCH₂Cl. On the other hand, both enantiomers of the corresponding (Z)-allylsilane were prepared from commercially available dimethylphenylvinylsilane through epoxidation, the regioselective epoxide-opening reaction with 1-propynylmagnesium bromide, and the subsequent optical resolution using a lipase.     

Pd-catalyzed cross-coupling reaction of (Z)- and (E)-bromoenyne: unusual stereochemical outcome

Pd-catalyzed cross-coupling reaction of (E)-bromoenyne 1Z with 1-alkyne and tributylvinyl-stannane occurs with retention of the configuration in benzene but with an inversion of the configuration in DMF or CH₂Cl₂. On the other hand, that of (Z)-bromoenyne 1E occurs with retention of the configuration in these solvents.     

Palladium-catalyzed isomerization of (Z)-1-functionalized-4-acetoxy-2-butenes: Solvent and substituent effects

The Pd(PPh₃)₄-catalyzed isomerization of (Z)-1,4-diacetoxy-2-butene, (Z)-1-(t-butyldimethylsilyloxy)-4-acetoxy-2-butene and (Z)-1-(t-butyldiphenylsilyloxy)-4-acetoxy-2-butene affords the corresponding (E)-isomers and 1,2-difunctionalized-3-butenes. In THF, the formation of the (E)-isomers is mainly due to reaction from an η¹-allylpalladium intermediate while an η³-allylpalladium is the main key intermediate in DMF. The time to reach equilibrium between the products and their respective concentrations depend on the nature of the substituents and the solvent.     

Synthesis of cis,cis,cis-1-alkylidene-2,3,4,5-tetrakis(diphenylphosphinomethyl)cyclopentanes

A new strategy to prepare tetradentate or pentadentate diphenylphosphine ligands has been explored from Diels-Alder adducts of fulvenes and maleic anhydride. A tetradentate phosphine ligand, bearing a side chain allowing the formation of a bond with polystyrene resin, has been prepared in seven steps from cyclopentadiene. The cis,cis,cis-1-cyclohexylidene-2,3,4,5-tetrakis(diphenylphosphinomethyl)cyclopentane (Cyclo-Tedicyp) in combination with [PdCl(C₃H₅)]₂ led to an efficient catalyst for the Heck, Suzuki and Sonogashira coupling reactions.     

(1R,2R)-DPEN-derived triazolium salts for enantioselective oxodiene Diels-Alder reactions

Enantioselective oxodiene Diels-Alder reactions catalyzed by (1R,2R)-DPEN-derived triazolium salts were realized successfully. With 0.5 mol % of (1R,2R)-DPEN-derived triazolium salt C and 150 mol % of Et₃N, the reactions of various α-chloroaldehydes (α-bromoaldehyde) with substituted enones led to 3,4-dihydropyridinones and their derivatives in good yields, diastereoselectivities, and enantioselectivities (up to 97% ee).     

Influence of hydrogen on the magnetic and electrical properties of GdI2Hx (0?x?1)

We have studied the effect of hydrogen insertion in GdI₂ on its magnetic and electrical properties. The ferromagnetic layered metal GdI₂ reversibly absorbs hydrogen with the formation of GdI₂H_x which exhibits a range of homogeneity 0?x?1. These phases crystallize with the hexagonal MoS₂-type heavy atom arrangement. Variation of the hydrogen content is accompanied by a monotonic change in the lattice parameters, and a decreases from 4.074(1) to 4.023(1) Å whereas c increases from 15.050(5) to 15.394(5) Å for x=0-0.97. The molar volume passes through a maximum at x≈0.35. Magnetization and resistance measurements reveal a substantial change in the physical properties of GdI₂H_x as a function of the hydrogen content, particularly as x approaches a critical value of ∼1/3. The Curie temperature rapidly decreases with increasing hydrogen content, and the long-range magnetic ordering is destroyed for x>0.33. The phases GdI₂H_x with 0.42?x?0.69 exhibit characteristics of a spin-glass below the magnetic freezing temperatures T_f=24 and 3 K for x=0.42 and 0.69, respectively. The hydride halides GdI₂H_x (x>0.19) show thermally activated conduction, accompanied by a steep increase of the activation energy at x≈0.33. The anomalies observed can be understood by assuming an ordering of the hydrogen atoms for x=1/3 within each layer.     

Laser photolysis study of trans→cis photoisomerization of trans-1-phenyl-2-(2-naphthyl) ethylene

The direct trans→cis photoisomerization of trans-1-phenyl-2-(2-naphthyl) ethylene (trans-PNE) in liquid solution at room temperature was studied by the nanosecond laser photolysis technique. The time-resolved S_n←S₁ and T_n←T₁ absorption spectra were observed with trans-PNE at 300 K and 77 K. The lifetime of the triplet state of trans-PNE was found to be much shorter in liquid solution at room temperature than in rigid solution at 77 K. This fact and the effect of a triplet quencher shows that the photoisomerization of trans-PNE occurs mainly via the triplet state.