Highly efficient nickel/phosphine catalyzed cross-couplings of diarylborinic acids with aryl tosylates and sulfamates

<正>4-Methoxy-4′-methylbiphenyl(3aa) [1] MeO White solid(0.324 g, 82% from aryl tosylate, 0.356 g, 90% from aryl sulfamate); m.p. 111–112 °C; 1H NMR(400 MHz,CDCl3) δ 7.50(d, J = 8.4 Hz, 2H), 7.44(d, J = 8.0 Hz, 2H), 7.21(d, J = 8.0 Hz, 2H), 6.95(d, J = 8.8 Hz, 2H), 3.82(s, 3H), 2.37(s, 3H); 13 C NMR(100 MHz, CDCl3) δ 159.0, 138.0, 136.4, 133.8, 129.5, 128.0, 126.6, 114.2, 55.4, 21.1. 4,4′-Dimethylbiphenyl(3ab) [1] White solid(0.320 g, 88% from aryl tosylate, 0.346 g, 95% from aryl sulfamate); m.p. 122–123 °C; 1H NMR(400 MHz,CDCl3) δ 7.47(d, J = 8.0 Hz, 4H), 7.22(d, J = 8.0 Hz, 4H), 2.37(s, 6H); 13 C NMR(100 MHz, CDCl3) δ 138.4, 136.8, 129.5, 126.9, 21.2.     

Preparation of ortho-substituted aryldifluorophosphines, 2-XC6H4PF2 (X = MeO or Me2N), and some of their derivatives. X-ray crystal structure determination of (2-MeOC6H4P)4 and of the platinum complex,Cl2Pt(2-MeOC6H4PF2)2

The preparation of the ortho-substituted aryldifluorophosphines 2-MeOC₆H₄PF₂ and 2-Me₂NC₆H₄PF₂ by chlorine-fluorine exchange from the corresponding dichlorophosphines using sodium fluoride in acetonitrile in the presence of a crown ether is described. The ortho-substituted aryldichlorophosphines 2-MeOC₆H₄PCl₂ and 2-Me₂NC₆H₄PCl₂ were prepared from the respective bis(N,N-dimethylamino) phosphines by cleavage of the PN bonds with hydrogen chloride. The reaction of 4-fluoroanisole and 2-methoxy-phenyllithium with phosphorus trichloride did not yield the expected chlorophosphines, i.e. 2-MeO-5-F-C₆H₃PCl₂ and 2-MeOC₆H₄PCl₂, but led to formation of 4-fluorophenyldichlorophosphite in the former, and to tris(2-methoxyphenyl)phosphine in the latter case. The difluorophosphine 2-MeOC₆H₄PF₂ was found to undergo a spontaneous oxidation-reduction reaction with formation of the tetrafluorophosphorane 2-MeOC₆H₄PF₄, and the cyclotetraphosphine (2-MeOC₆H₄P)₄. A single-crystal X-ray structure determination of the latter indicated the presence of a strongly puckered four-membered ring with PP bond lengths ranging between 222 and 223 pm, and endocyclic bond angles of 84°. Vicinal MeOC₆H₄ groups were found arranged trans to each other. Dichloroplatinum(II) complexes were prepared, involving the two new fluorophosphines, 2-XC₆H₄PF₂ (X = MeO or Me₂N), as ligands. In neither case was any evidence found for coordination between platinum and oxygen or nitrogen, and the fluorophosphines were found to function solely as phosphorus donors. The absence of interaction between platinum and the oxygen atom in the ortho position of the ligand 2-MeOC₆H₄PF₂ was confirmed in a single-crystal X-ray determination of the complex Cl₂(2-MeOC₆H₄PF₂)₂Pt. The compound was found to exist as a planar, cis-coordinated species with PtCl bond lengths between 232 and 234 pm, and a PtP bond length of 218 pm. All compounds were characterized by NMR spectroscopy (¹H, ³¹P and ¹⁹F, where applicable).     

Bulky Cations and Four different Polyiodide Anions in [Lu(Db18c6)(H2O)3(thf)6]4(I3)2(I5)6(I8)(I12)

Black single crystals of [Lu(Db18c6)(H₂O)₃(thf)₆]₄(I₃)₂(I₅)₆(I₈)(I₁₂) were obtained from lutetium, I₂ and Db18c6 (dibenzo‐18‐crown‐6) in THF solution. In the bulky cation, Lu³⁺ is surrounded by nine oxygen atoms, six of Db18c6 and three of water molecules to which two THF molecules are attached each. Meanwhile, four polyiodide anions, (I₃)^–, (I₅)^–, (I₈)^2– and (I₁₂)^2–, in a 2:6:1:1 ratio form a three‐dimensional network and leave space for the bulky cations.     

Syntheses,spectroscopy, and X-ray structures of 3-{(R)-(Ar)-ethylimino}-1,3-dihydro-indol-2-one (Ar = Ph,MeOC6H4, BrC6H4, 1-naphthyl) and [Rh(η4-cod){3-((R)-(Ar)-ethylimino)-3H-indol-2-olato}]

Condensation of 1H-indole-2,3-dione (isatin) with (R)-(Ar)-ethylamines gives enantiopure Schiff bases, 3-{(R)-(Ar)-ethylimino}-1,3-dihydro-indol-2-one (HL) {Ar?=?Ph (HL1), 2-MeOC₆H₄ (HL2), 4-MeOC₆H₄ (HL3), 4-BrC₆H₄ (HL4), and 1-naphthyl (HL5)}. The Schiff bases readily coordinate to [Rh(μ-O₂CMe)(η⁴-cod)]₂ (cod?=?1,5-cyclooctadiene) to give mononuclear [Rh(η⁴-cod){3-((R)-(Ar)-ethylimino)-3H-indol-2-olato}] {Ar?=?Ph (1), 4-MeOC₆H₄ (2), and 4-BrC₆H₄ (3)}, respectively. The Schiff bases and complexes have been fully characterized by IR, UV-Vis, ¹H-NMR, mass, and circular dichroism (CD) spectrometry. Polarimetry and CD measurements show the enantiopurity of the Schiff bases as well as the complexes. ¹H NMR measurements reveal slow conversion of the lactam to the enol form of the Schiff bases in solution. In the solid state the lactam form dominates as shown by crystal structures of HL1 and HL4. While gross structural features of both are similar, the molecules differ significantly in the relative orientations of the aryl and lactam rings. The difference is mostly rotation about the N2–C9 bond with different C8–N2–C9–C11 torsion angle of +89.77(12)° for HL1 and C2–N2–C9–C11 of +106.8(3)° for HL4.     

Monovalent Group 13 Organometallic Compounds: Weak Association to Monomeric,Versatile Two-Electron Donors

A weakly associated hexamer is formed for [GaCp*] (Cp*=C₅Me₅) in the solid state (see picture). The recent X-ray crystal structure analyses of [GaCp*] as well as the monomeric In^I and Tl^I compounds [M(2,4,6-Trip₃C₆H₂)] (Trip=2,4,6-iPr₃C₆H₂) throw new light on the association and aggregation of monovalent Group 13 elements in the solid state. The synthesis of [Ni⁰{In[C(SiMe₃)₃]}₄], a complex with terminally bonded In^IR ligands, offers alternative σ-donor/π-acceptor ligands to organometallic chemists. The newest results in this area are likely to open up new and intriguing possibilities in the preparation of main group–transition metal clusters.     

Structural Studies on some Iodoantimonate and Iodobismuthate Anions

The reaction between BiI₃ and two equivalents of dmpu (dmpu = N,N′-dimethylpropylene urea) in thf (tetrahydrofuran) or toluene affords dark red crystals of the complex [Bi(dmpu)₆][Bi₃I₁₂] which was characterised by X-ray crystallography and consists of octahedral [Bi(dmpu)₆]³⁺ cations and [Bi₃I₁₂]^3? anions both with 3 symmetry. An analogous reaction between SbI₃ and dmpu afforded orange crystals of what is probably a hydrolysis product, [C₅NH₆]₂[H(dmpu)₂][Sb₂I₉], which was also characterised by X-ray crystallography and contains a face-shared bioctahedral [Sb₂I₉]^3? anion with two pyridinium cations and a hydrogen bonded [H(dmpu)₂]⁺ cation. [CH₂?C(C₆H₄-4-NO₂)CH₂NMe₃]I and one equivalent of SbI₃ afforded the orange crystalline complex [CH₂?C(C₆H₄-4-NO₂)CH₂NMe₃]₃[Sb₂I₉] an X-ray crystallographic study of which revealed a face-shared bioctahedral [Sb₂I₉]^3? anion similar to that present in [C₅NH₆]₂[H(dmpu)₂][Sb₂I₉]. Four equivalents of BiI₃ and [CH₂?C(C₆H₄-4-NO₂)CH₂NMe₃]I afforded the complex [CH₂?C(C₆H₄-4-NO₂)CH₂NMe₃]₃[Bi₃I₁₂], the [Bi₃I₁₂]^3? anion being essentially identical to that encountered in [Bi(dmpu)₆][Bi₃I₁₂]. [CH₃(CH₂)₂COS(CH₂)₂NMe₃]I and four equivalents of SbI₃ yielded orange crystals of the complex [CH₃(CH₂)₂COS(CH₂)₂NMe₃]₄[Sb₈I₂₈] which was also characterised by X-ray crystallography and shown to contain a new structural type of [E₈X₂₈]^4? anion (E = As, Sb, Bi; X = halide).     

Metallkomplexe von Farbstoffen. VIII Übergangsmetallkomplexe des Curcumins und seiner Derivate

Metal Complexes of Dyes. IX. Transition Metal Complexes of Curcumin and Derivatives The bidentate monoanions of curcumin[CU, (1, 7-bis(4-hydroxy-3-methoxyphenyl)-hepta-1,6-diene-3,5-dione)], diacetylcurcumin[DACU, (1,7-bis(4-acetyl-3-methoxyphenyl)-hepta-1,6-diene-3,5-dione)], dihydroxycurcumin[DHCU, (1,7-bis(4-hydroxiphenyl)-hepta-1,6-diene-3,5-dione)], dimethylcurcumin [DMCU, (1,7-bis(3,4-dimethoxyphenyl)-hepta-1, 6-diene-3,5-dione)] and trimethylcurcumin[TMCU, (1,7-bis(3,4-dimethoxyphenyl)-4-methylhepta-1,6-diene-3,5-dione)] form with chloro bridged complexes [(R₃P)MCl₂]₂ (M?Pd, Pt; R?phenyl, n-butyl, ethyl, tolyl), [η⁵-C₅Me₅)MCl₂]₂ (M?Rh, Ir), [(η⁶-p-cymene)RuCl₂]₂, [(η³-C₃H₅)PdCl]₂, di-μ-chlorobis[N-(diphenylmethylene)-glycinethylester-(C,N)]-dipalladium(II) and with [(η⁵-C₅Me₅)Co(CO)I₂] monochelate dye complexes. The structure of [(η⁶-p-cymene)(Cl)Ru(DMCU)] was determined by X-ray diffraction. The dichelates (DMCU)₂M with M?Cu, Ni, (CU)₂Pd and the trichelate (CU)₃Fe were obtained. Cationic bipyridine copper(II) complexes with CU, DHCU, and DMCU were sythesized by treating the dye ligands with copper(II) acetate, 2,2′-bipyridine and ammoniumtetrafluoroborate. In comparison to the free 1.3-diketones the dye complexes show a bathochromic shift in the UV/VIS spectra.     

Arene complexes [(η-C<Subscript>5</Subscript>H<Subscript>5</Subscript>)M(η-C<Subscript>6</Subscript>R<Subscript>6</Subscript>)]<Superscript>2+</Superscript> (M = Rh,Ir)

The dicationic arene complexes [CpM(arene)](BF₄)₂ (arene = C₆H₆, 1,3,5-C₆H₃Me₃, or C₆Me₆) were synthesized by the reactions of the solvated complexes [CpM(MeNO₂)₃](BF₄)₂ (M = Rh, Ir) with benzene and its derivatives. The solvated complexes were generated in situ by abstraction of I^– from [CpMI₂]₂ with AgBF₄. A procedure was developed for the synthesis of the iodide [CpRhI₂]₂ based on the reaction of the cyclooctadiene derivative CpRh(1,5-C₈H₁₂) with I₂. The structure of the [CpRh(C₆Me₆)](BF₄)₂ complex was established by X-ray diffraction analysis.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1871–1874, September, 2004.     

The mannich reaction in the synthesis of N,S-containing heterocycles 4. Aminomethylation of 6-amino-3,5-dicyano-1,4-dihydropyridine-2-thiolates: A convenient regioselective route to 3,5,7,11-tetraazatricyclo[7.3.1.02,7]tridec-2-ene derivatives

Treatment of N-methylmorpholinium 4-R-6-amino-3,5-dicyano-1,4-dihydropyridine-2-thiolates (R = 2-ClC₆H₄ and 2-MeOC₆H₄) with primary amines in the presence of an excess of formaldehyde gave 13-R-8-thioxo-3,5,7,11-tetraazatricyclo[7.3.1.0^2,7]tridec-2-ene-1,9-dicarbonitrile derivatives in high yields (66–95%). In a similar way, aminomethylation of 3-R-10-amino-7,11-dicyano-9-aza-3-azoniaspiro[5.5]undeca-7,10-diene-8-thiolates (R = Me and Et) afforded 1′-alkyl-8-thioxospiro[3,5,7,11-tetraazatricyclo[7.3.1.0^2,7]tridec-2-ene-13,4′-piperidine]-1,9-dicarbonitriles in 43–91% yields. Alternatively, these compounds were obtained by multicomponent cyclocondensation of N-alkylpiperidin-4-ones, cyanothioacetamide, primary amines, and aqueous formaldehyde. The starting 3-R-10-amino-7,11-dicyano-9-aza-3-azoniaspiro[5.5]undeca-7,10-diene-8-thiolates were prepared by a new method from N-alkylpiperidin-4-ones and cyanothioacetamide. The structure of 5,11-bis(4-ethoxyphenyl)-13-(2-methoxyphenyl)-8-thioxo-3,5,7,11-tetraazatricyclo[7.3.1.0^2,7]tridec-2-ene-1,9-dicarbonitrile was examined by X-ray diffraction analysis. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1014–1022, May, 2007.     

The structural diversity of Te-I interactions within tetraorganoditelluroxane diiodides and related compounds

Two tetraorganoditelluroxane diiodides (R₂Te)₂OI₂ (3, R = p-MeOC₆H₄; 5, R = Me) were prepared by the reaction of (p-MeOC₆H₄)₂TeI₂ (1) and (p-MeOC₆H₄)₂TeO (2) and the base hydrolysis of Me₂TeI₂ (4), respectively. The base hydrolysis of C₄H₈TeI₂ (8) afforded the tritelluroxane diiodide (C₄H₈Te)₃O₂I₂ (9). The reaction of Me₂TeI₂ (4) and Me₂Te(OH)₂ (6) in a ratio of 1:3 produced the coordination polymer of the composition 2 (Me₂Te)₂O(I)OH · H₂O (7). An attempt at preparing an adduct of 3 with iodine failed but provided co-crystals of (p-MeOC₆H₄)₂TeI₂ · I₂ (1a). The supramolecular structures of 1a, 3, 5, 7 and 9 are dominated by structurally directing secondary Te?I interactions.     

Synthesis of 2-substituted 1-tosyl-3-(1-tosyliminoalkyl)imidazolidines and-hexahydropyrimidines

Reactions of N-tosylimidoyl chlorides with the Schiff bases of the general formula TsNH(CH₂)_nN=CHR (n = 2 or 3; R = Prⁱ, 4-MeOC₆H₄, 4-Me₂NC₆H₄, and 3-O₂NC₆H₄) afforded 2-substituted 1-tosyl-3-(1-tosyliminoalkyl)imidazolidines (n = 2) or-hexahydropyrimidines (n = 3). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 872–875, May, 2006.     

Understanding the Subtleties of Frustrated Lewis Pair Activation of Carbonyl Compounds by N‐Heterocyclic Carbene/Alkyl Gallium Pairings

This study reports the use of the trisalkylgallium GaR₃ (R=CH₂SiMe₃), containing sterically demanding monosilyl groups, as an effective Lewis‐acid component for frustrated Lewis pair activation of carbonyl compounds, when combined with the bulky N‐heterocyclic carbene 1,3‐bis(tert‐butyl)imidazol‐2‐ylidene (ItBu) or 1,3‐bis(tert‐butyl)imidazolin‐2‐ylidene (SItBu). The reduction of aldehydes can be achieved by insertion into the C=O functionality at the C2 (so‐called normal) position of the carbene affording zwitterionic products [ItBuCH₂OGaR₃] ( 1 ) or [ItBuCH(p‐Br‐C₆H₄)OGaR₃] ( 2 ), or alternatively, at its abnormal (C4) site yielding [aItBuCH(p‐Br‐C₆H₄)OGaR₃] ( 3 ). As evidence of the cooperative behaviour of both components, ItBu and GaR₃, neither of them alone are able to activate any of the carbonyl‐containing substrates included in this study NMR spectroscopic studies of the new compounds point to complex equilibria involving the formation of kinetic and thermodynamic species as implicated through DFT calculations. Extension to ketones proved successful for electrophilic α,α,α‐trifluoroacetophenone, yielding [aItBuC(Ph)(CF₃)OGaR₃] ( 7 ). However, in the case of ketones and nitriles bearing acidic hydrogen atoms, C?H bond activation takes place preferentially, affording novel imidazolium gallate salts such as [{ItBuH}⁺{(p‐I‐C₆H₄)C(CH₂)OGaR₃}^?] ( 8 ) or [{ItBuH}⁺{Ph₂C=C=NGaR₃}^?] ( 12 ).     

SYNTHESIS OF NOVEL BIDENTATE (Te,N) LIGANDS-2-ARYLTELLUROETHYLAMINES AND THEIR COMPLEXATION WITH MERCURY (II)

Abstract

Sodium aryltellurolate (ArTe^?Na⁺, where Ar = 4-MeOC₆H₄ or 4-EtOC₆H₄) reacts with 2- bromoethylamine resulting in the (Te, N) ligands 2-aryltelluroethylamine (ArTeCH₂CH₂NH₂, 1) which have been characterized by elemental analyses, molecular weight, IR, ¹H and ¹³C NMR spectra. With HgCI₂, they form HgC1₂·1 type of complexes. IR, ¹H and ¹³C NMR spectra of the complexes suggest that 1 ligates as a bidentate ligand with respect to Hg(II). Osmometric molecular weight measurements suggest that on heating the mercury complex HgCl₂·lb (Ar = 4-EtOC₆H₄) in solution, relatively less soluble species result. It seems to have two Hg atoms bridged by two (Te, N) ligands. The HgC₂·la (Ar = 4-MeOC₆H₄) has very low solubility in organic solvents and. therefore, seems to be dimerized or polymerized during the synthesis. Analysis of CH₂ rocking bands in IR spectra suggests that two CH₂ groups of the ligands are most probably in a gauche conformation in the mercury complexes.     

Some reactions with ω-bromoacetophenone: Synthesis of Δαβ-butenolide and its transformation into pyrrole derivatives

ω-Bromoacetophenone reacts with the sodium salt of ethyl cyanoacetate to afford α-cyano-β-phenyl-Δ^αβ-butenolide. This butenolide undergoes azo coupling with diazotized aromatic amines (ArNH₂) to afford the hydrazo derivatives. These hydrazo derivatives (ArPh, 4-ClC₆H₄, 4-MeC₆H₄, 4-MeOC₆H₄) were transformed into the corresponding 3(2H)-pyridazinone derivatives on stirring in methanol in the presence of potassium hydroxide. These latter compounds were converted into the corresponding 3-cyano-2,5-dihydroxy-4-phenyl-N-arylpyrrole derivatives on reduction with zinc dust in refluxing acetic acid, presumably via reductive cleavage of the N N bond of the pyridazine followed by recyclization via loss of ammonia.     

Tris(5-bromo-2-methoxyphenyl)bismuth bisbenzenesulfonate solvate with toluene: Synthesis and structure

Tris(5-bromo-2-methoxyphenyl)bismuth bisbenzenesulfonate, which crystallizes from toluene in the solvate form (5-Br-2-MeOC₆H₃)₃Bi(OSO₂Ph)₂ ? TolH (I), has been synthesized by the reaction between tris(5-bromo-2-methoxyphenyl)bismuth and benzenesulfonic acid in the presence of hydrogen peroxide (1: 2: 1 mol/mol/mol) in ether. A crystal contains two types of crystallographically independent molecules (a and b), in which bismuth atoms have a trigonal bipyramidal coordination to benzenesulfonate substituents in axial positions. The axial OBiO angle is 175.4(3)° (Ia) and 175.5(3)° (Ib), and the equatorial CBiC angles are 111.2(3)°, 122.0(4)°, 126.7(4)° (Ia) and 111.3(4)°, 123.3(3)°, 125.2(4)° (Ib). The Bi–C distances are 2.189(9), 2.198(9), 2.200(10) Å (Ia) and 2.198(9), 2.202(9), 2.209(9) Å (Ib). The Bi–O bond lengths are 2.274(8), 2.306(8) Å (Ia) and 2.248(8), 2.303(8) Å (Ib). Intramolecular contacts between the bismuth atom and the oxygen atoms of methoxy and sulfonate groups take place in molecules.     

The first example of a complex of N-perfluoroarylated azacrown ether: The crystal structure of diaqua{<Emphasis Type="Italic">N,N′</Emphasis>-bis(tetrafluoropyridyl)diaza-18-crown-6}lead(II) perchlorate

Complex formation of lead(II) perchlorate with N,N′-diaryldiaza-18-crown-6 (aryl = C₆H₅, 4-MeOC₆H₄, 4-C₅F₄N) has been studied. The stability of the complexes decreases with an increase in the electron-withdrawing character of the aryl substituent in the series (logβ, methanol): 4-MeOC₆H₄ (4.7), C₆H₅ (2.7), 4-C₅F₄N (<0 in methanol, 0.9 in acetone-d ₆). The dihydrate complex of lead(II) perchlorate with N,N′-bis(tetrafluoropyridyl)diaza-18-crown-6 (L) [Pb(L)(H₂O)₂](ClO₄)₂ has been studied by X-ray crystallography. The crystals are monoclinic, a = 9.260(2) Å, b = 16.986(2) Å, c = 21.620(3) Å, β = 96.01(2)°, V = 3381.9(9) ų, Z = 4, space group P2₁/n, R = 0.0449 for 5126 reflections with I > 2σ(I). In the complex cation [Pb(L)(H₂O)₂]²⁺, the coordination geometry of the metal atom is determined by partial delocalization of the lone pair. The Pb atom is asymmetrically bound to four oxygen atoms of substituted diaza-18-crown-6 and two oxygen atoms of water molecules (Pb-O, 2.450–2.726 Å). The CN of the metal atom is completed to ten by two nitrogen atoms of the macrocycle and two ortho fluorine atoms of two tetrafluoropyridyl substituents of the ligand L at longer distances (Pb-N, 2.978 and 3.108 Å; Pb-F, 2.890 and 3.123 Å).     

Co(II) and Ni(II) complexes with imidazole-containing ligands: Synthesis,structural characterization,and magnetic property

Hydrothermal reaction of Co(II) salt with 1,4-di(1-imidazolyl)benzene (L¹) and 4,4’-oxydiphthalic acid (H₄OA) yields a new complex [Co₃(HOA)₂(L¹)₄(H₂O)₄] (I). [Ni(L²)₂SO₄] · 0.5H₂O (II) can be obtained via the hydrothermal reaction of NiSO₄ · 6H₂O with 1,3-di(1H-imidazol-4-yl)benzene (L²). Complexes I and II have been characterized by single-crystal and powder X-ray diffraction (CIF files CCDC nos. 1019291 (I) and 1019292 (II)), IR, elemental, and thermogravimetric analyses. Complex I exhibits the uninodal six-connected 3D pcu framework structure of I with (4¹² · 6³) topology; Complex II consists of the uninodal four-connected 2D sql (4⁴ · 6²) networks. In addition, magnetic property of I was investigated.     

peri-Interaction between diarylmethyl and diarylmethylium units in 1,8-disubstituted naphthalenes: preference of localized structure for the C-H bridged carbocation

(8-Diarylmethyl-1-naphthyl)bis(4-dimethylaminophenyl)methyliums (aryl=C₆H₅, 4-IC₆H₄, and 4-MeOC₆H₄) were generated by hydride shift from (4-dimethylaminophenyl)methyl group to the diarylmethylium unit at peri-positions of naphthalene. Successful isolation and low-temperature X-ray analysis indicated that they are novel C-H bridged carbocations, which prefer the localized structure with a short contact of C-H?C⁺ rather than the delocalized one with a three-centered-two-electron bond of (C?H?C)⁺.     

Synthetic access to optically active isoflavans by using allylic substitution

A general approach to the (S)- and (R)-isoflavans was invented, and efficiency of the method was demonstrated by the synthesis of (S)-equol ((S)-3), (R)-sativan ((R)-4), and (R)-vestitol ((R)-5). The key step is the allylic substitution of (S)-6a (Ar¹=2,4-(MeO)₂C₆H₃) and (R)-6b (Ar¹=2,4-(BnO)₂C₆H₃) with copper reagents derived from CuBr·Me₂S and Ar²-MgBr (7a, Ar²=4-MeOC₆H₄; 7b, 2,4-(MeO)₂C₆H₃; 7c, 2-MOMO-4-MeOC₆H₃), furnishing anti S_N2′ products (R)-8a and (S)-8b,c with 93-97% chirality transfer in 60-75% yields. The olefinic part of the products was oxidatively cleaved and the Me and Bn groups on the Ar¹ moieties was then removed. Finally, phenol bromide 9a and phenol alcohols 9b,c underwent cyclization with K₂CO₃ and the Mitsunobu reagent to afford (S)-3 and (R)-4 and -5, respectively.     

Stability and structure in solution of potassium and barium complexes with N,N’-diaryldiaza-18-crown-6: Crystal structure of N,N’-Bis(4-dimethylaminophenyl)diaza-18-crown-6 and its complex with barium perchlorate

It has been shown that N,N’-diaryldiaza-18-crown-6 ethers with p-dimethylamino-and p-methoxy groups in the benzene ring (aryl is 4-Mc₂NC₆H₄) (I) and 4-MeOC₆H₄ (II) form complexes with potassium and barium salts. The influence of these salts on the UV and ¹H NMR spectra of crown ethers I and II has been studied. The stability constants (logβ) of the complexes increase in the series II · Ba(ClO₄)₂ (2.0), I · Ba(ClO₄)₂ (2.3), II · KBr (2.8), I · KBr (3.0). N,N’-bis(4-dimethylphenylamine)diaza-18-crown-6 (L, I) and its complex with barium perchlorate Ba(ClO₄)₂ · L (III) are characterized by X-ray crystallography. The crystals of I are monoclinic: a = 13.778(2) Å, b = 5.9731(9) Å, c = 17.542(3) Å, β = 106.65(1)°, V = 1383.1(4) ų, Z = 2, space group P2₁/n, R = 0.0374 for 990 reflections with I > 2σ(I). The crystals of III are monoclinic: a = 17.275(4) Å, b = 8.017(2) Å, c = 26.935(4) Å, β = 100.47(2)°, V = 3669(1) ų, Z = 4, space group C2/c, R = 0.0320 for 1897 reflections with I > 2σ(I). The molecules of I and III are centrosymmetric. In III, the Ba atom is in the center of substituted diaza-18-crown-6 (DA18C6). The Ba atom is coordinated by all six donor atoms of diaza-18-crown-6 (av. Ba-O, 2.779(3) Å; Ba-N, 3.004(4) Å) and four oxygen atoms of two asymmetrically bound perchlorate groups (Ba-O, 2.832(4) and 3.031(4) Å) arranged below and above the plane of substituted diaza-18-crown-6. The conformations of the macrocycle in free and coordinated L are different.