E. V. Vorontsov

Regioselective Fries Rearrangement and Friedel−Crafts Acylation as Efficient Routes to Novel Enantiomerically Enriched ortho-Acylhydroxy[2.2]paracyclophanes

Two useful approaches to ortho-acylhydroxy[2.2]paracyclophanes, starting from 4-hydroxy[2.2]paracyclophane, have been developed. TiCl4-catalyzed Fries rearrangement and direct acylation occur regioselectively (to the ortho position with respect to the hydroxy group), leading to 4-acetyl-5-hydroxy[2.2]paracyclophane (3) and 4-benzoyl-5-hydroxy[2.2]paracyclophane (4) in high to excellent chemical yields. For compound 4, an X-ray investigation has been performed. ortho-Acylhydroxy[2.2]paracyclophanes 3 and 4 have been obtained in enantiomerically enriched forms (ee 92−99%) and the absolute configurations of their enantiomers have been determined.

In situ IR and NMR study of the interactions between proton donors and the Re(I) hydride complex [{MeC(CH2PPh2)3}Re (CO)2H]. ReH…H bonding and proton-transfer pathways

Abstract The reactions of various proton donors (phenol, hexafluoro-2-propanol, perfluoro-2-methyl-2-propanol, monochloroacetic acid, and tetrafluoroboric acid) with the rhenium (I) hydride complex [(triphos)Re(CO)2H] (1) have been studied in dichloromethane solution by in situ IR and NMR spectroscopy. The proton donors from [(triphos)Re(CO)2H…HOR] adducts exhibiting rather strong H…H interactions. The enthalpy variations associated with the formation of the H-bonds (−ΔH = 4.4–6.0 kcal mol−1) have been determined by IR spectroscopy, while the H…H distance in the adduct [(triphos)Re(CO)2H…HOC(CF3)3] (1.83 A) has been calculated by NMR spectroscopy through the determination of the T1min relaxation time of the ReH proton. It has been shown that the [(triphos)Re(CO)2H…HOR] adducts are in equilibrium with the dihydrogen complex [(triphos)Re(CO)2(η2-H2)]+, which is thermodynamically more stable than any H-bond adduct.

Symmetrically tetrasubstituted [2.2]paracyclophanes: their systematization and regioselective synthesis of several types of bis-bifunctional derivatives by double electrophilic substitution.

The possible number of chiral and achiral tetrasubstituted [2.2]paracyclophanes possessing different types of symmetry (C(2), C(i), C(s), C(2v), C(2h)) is evaluated and a unified independent trivial naming descriptor system is introduced. The reactivity and regioselectivity of the electrophilic substitution of the chiral pseudo-meta- and achiral pseudo-para-disubstituted [2.2]paracyclophanes are investigated in an approach suggested to be general for the synthesis of bis-bifunctional [2.2]paracyclophanes. The mono- and diacylation of chiral pseudo-meta-dihydroxy[2.2]paracyclophane 14 with acetylchloride occur ortho-regioselectively to produce tri- 22, 23 and symmetrically 21 tetrasubstituted acyl derivatives. The same reaction with benzoylchloride is neither regio-, nor chemoselective, and gives rise to a mixture of ortho-/para-, mono-/diacylated compounds 27-31. The double acylation of pseudo-meta-dimethoxy[2.2]paracyclophane 18 is completely para-regioselective. Electrophilic substitution of pseudo-meta-bis(methoxycarbonyl)[2.2]paracyclophane 20 regioselectively generates the pseudo-gem-substitution pattern. Formylation of this substrate produces the monocarbonyl derivatives 35 only, whereas the Fe-catalyzed bromination may be directed towards mono- 36 or disubstitution 37 products chemoselectively by varying the reactions conditions. The diacylation and dibromination reactions of the respective achiral diphenol 12 and bis(methoxycarbonyl) 40 derivatives of the pseudo-para-structure retain regioselectivities which are characteristic for their pseudo-meta-regioisomers. Imino ligands 26, 25, and 39, which were obtained from monoacyl- 22 and diacyldihydroxy[2.2]paracyclophanes 21, 38, are tested as chiral ligands in stereoselective Et(2)Zn addition to benzaldehyde producing 1-phenylpropanol with ee values up to 76 %.

Resolution and Novel Reactions of 4-Hydroxy[2.2]paracyclophane

The resolution of racemic 4-hydroxy[2.2]paracyclophane (1) by fractional crystallization of the diastereomeric esters 3 with (1S)-(−)-camphanic acid and the determination of the absolute configurations of (R)- and (S)-4-hydroxy[2.2]paracyclophanes by X-ray diffraction have been carried out. The Friedel−Crafts oxaloylation of 1 with AlCl3 was found to occur with formation of both ortho- and para-hydroxy[2.2]paracyclophanylglyoxylic acids, whereas in the presence of TiCl4, quantitative formation of 2,3-dioxo-2,3-dihydrofurano[4,5-d][2.2]paracyclophane (8) as a product of an unusual cooperative C- and O-acylation was observed. Replacement of the OH group in the substrate for OCH3 (compound 18) changes the regioselectivity of the oxaloylation, which now occurs with formation of a para-substituted α-diketone 19. A novel technique for the synthesis of 4-formyl-5-hydroxy[2.2]paracyclophane (FHPC, 15) involving stereoselective reduction of 8 followed by oxidative cleavage of the intermediate diol 14 is also presented.

Elaboration of a novel type of planar-chiral methylene bridged biphenols based on [2.2]paracyclophanes

Abstract A new class of chiral methylene bridged biphenols with planar chirality has been designed and elaborated. The synthetic approach is based on the use of 4-hydroxy-5-hydroxymethyl[2.2]paracyclophane 9 derived from either racemic or enantiomerically pure ( S ) - 4 - formyl-5-hydroxy[2.2.]paracyclophane (FHPC) by reduction with LiAlH 4 . The condensation of 9 with chiral racemic 4-hydroxy[2.2]paracyclophane 4 and achiral phenols, such as 2,5-dimethylphenol 10 and 2-isopropyl-5-methylphenol 11 , afforded the target bridged biphenols 6 , 12 and 13 , respectively. The preliminary results on the asymmetric addition of Et 2 Zn to benzaldehyde promoted by ( S,S ) - 6 are reported.

A new family of planar-chiral symmetric and unsymmetric salens based on the [2.2]paracyclophane skeleton

Planar-chiral ortho-hydroxy[2.2]paracyclophanyl ketones as well as ortho-hydroxy[2.2]paracyclophanyl aldehyde were employed as building blocks for the design of a new family of chiral salen type ligands in which the chiral environment can be organized by the planar chiral fragments of [2.2]paracyclophane and modified by introduction of the chiral diamine part. A new family of four different types of chiral salens was successfully synthesized using both direct and stepwise approaches.

A novel class of bidentate ligands with a conformationally flexible biphenyl unit built into a planar chiral [2.2]paracyclophane backbone

Abstract We report the synthesis of a novel class of planar chiral bidentate aryl[2.2]paracyclophane ligands. For the first time in the [2.2]paracyclophanyl series the Pd-catalyzed Suzuki cross-coupling was employed for the formation of the arylparacyclophanyl skeleton. From the two possible approaches: (a) cross-coupling of [2.2]paracyalophanylboronic acids with aryl halides; (b) cross-coupling of [2.2]paracyclophanyl halides with arylboronic acids, the latter was found to be more efficient. This approach was successfully used for the synthesis of a wide range of aryl[2.2]paracyclophanes with different types of substitution patterns (ortho-, pseudo-ortho- or pseudo-gem-arrangement of the functionally-substituted aryl fragment with respect to the substituent in the paracyclophane ring).

Asymmetric synthesis of (R,S)- and (R,R)-4-hydroxy-5-(α-substituted)-hydroxymethyl[2.2]paracyclophane and derivatives by stereoselective addition to (R)-4-hydroxy-5-formyl[2.2]paracyclophane and derivatives

Abstract Highly diastereoselective nucleophilic addition reactions of organometallic reagents to formyl[2.2]paracyclophane derivatives which were ortho-substituted by hydroxy-, alkoxy- and trimethylsilyloxy-groups are reported. The absolute configuration of the newly formed secondary alcohols is assigned on the basis of the X-ray diffraction study as well as chemical correlation. The magnitude of the asymmetric induction and even the sense of chirality of the forming asymmetric carbon atoms of the alcohols depended on the nature of the ortho-substituents.

Protonation of triosmium clusters Os3(CO)9(μ−CO)(μ3−2σ,η2−HCCR) and Os3(μ−H)(CO)9(μ3−σ,2η2−CCR) (R = CH2OH, CMe2OH, C(Me) = CH2

Abstract Protonation of Os3(CO)(μ−CO(μ3−2σ,η2−HCCR) (R = CH2OH (1) R = CMe2OH (2) and Os3(μ−H)(CO)9(μ3−σ,2η2−CCR) (R = CH2OH (3), R = CMe2OH (4), R = C(Me) = CH2 (5)) affords cationic complexes with the 5e-and 6e-propargyl ligands [Os3(CO)9(μ−CO)(μ3−3σ,η2−HCCCR′2)]+ (R′ = H (6), R′ = Me ( 7 ) and [Os3(μ−H)(CO)9(μ3−2σ,2η2−CCR′2)+ ( R′ = H ( 8 ) , R′ = Me ( 9 ) respectively. Reactrions of the cationic complexes with PPh3 were studied. The treatment of solutions of complexes 6–9 with triphenylphosphine leads to the phosphonium derivatives of the Os3 clusters Os 3 ( CO ) 9 (μ 2 −2σ,η 2 - HC  CCR ′ 2 P + Ph 3 ) ( R ′ = H , (10); R ′ = Me, ( 11 )) as well as complexes Os 3 (μ- H(CO ) 9 (μ 3 −σ,2η 2 − P + Ph in3 CCCR ′ 2 ) ( R = H ( 12 , R ′ = Me ( 13 )) with the novel phosphonium allenyl ligand. The cluster Os3(CO)8(μ−CO){HC2[C(Me)CH2]COC[C(Me)CH2]CH} (4) synthesized and its X-ray study was carried out (R = 0.0504 for 5510 observed reflections). Crystals of 14 are triclinic, at 20°C: a = 8.591(2), b = 11.437(2), c = 12.642(3) A , α = 93.17(2), β = 104.67(2), γ = 101.83(2)°, V = 1168.6(4) A , d calc = 2.793 g cm −3 , Z = 2 , space group P 1 .

Hydrogen bonding and proton transfer involving the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) and fluorinated alcohols: the competitive role of the hydride ligands and metal

The protonation of complexes Cp*M(dppe)H3 (dppe is ethylenebis(diphenylphosphine), M = Mo (1), W (2)) by a variety of fluorinated alcohols of different acid strength (FCH2CH2OH, CF3CH2OH, (CF3)2CHOH, and (CF3)3COH) was investigated experimentally by the variable temperature spectroscopic methods (IR, NMR) and stopped-flow technique (UV-Vis). The structures of the hydrogen-bonded and proton transfer products were studied by DFT calculations. In agreement with the calculation results, the IR data suggest that the initial hydrogen bond is established with a hydride site for complex 1 and with the metal site for complex 2. However, no intermediate dihydrogen complex found theoretically was detected experimentally on the way to the final classical tetrahydride product.