Facile synthesis of optically active imidazole derivatives

Five optically active imidazole derivatives have been synthesized via a facile 4-step reaction sequence starting from commercially available and inexpensive N-Cbz amino acids. While microwave assisted condensation was unsuccessful, the condensation of the corresponding alpha-bromoketones with formamidine acetate in liquid ammonia was revealed to be a useful method for the synthesis of such imidazole derivatives. The derivatives thus prepared are structurally-related to histamine.     

Synthesis of optically active verrucarinic acid derivatives

Two syntheses of verrucarinic acid highlighting an oxidative cleavage of hydroxysulfides and use of mandelate esters for chromatographic resolution are reported.     

Synthesis of optically active amphiphilic tetrathiafulvalene derivatives

The synthesis and characterization of novel chiral tetrathiafulvalenes bearing two long alkyl chains at one end of the π-electron rich unit and different functional groups—ester, acid or thiolate—at the other extreme is described. The synthetic method requires the preparation of 1,3-dithiol derivatives with two stereogenic centers. Different routes and reaction conditions were explored to form these compounds, whose optimized synthesis involved the nucleophilic substitution of a chiral bromo methylene derivative with tetrabutylammonium bis(2-thioxo-1,3-dithiole-4,5-dithiolate)zincate. The tetrathiafulvalenes were prepared by coupling the 1,3-dithiol derivative with 4,5-bis(methoxycarbonyl)-1,3-dithiol-2-one or 4,5-bis(2-cyanotehylthio)-1,3-dithiol-2-thione. The products were fully characterized, including by circular dichroism spectroscopy, which confirmed their optical activity. They are promising candidates to be used as building blocks in supramolecular materials for molecular electronics, to produce systems with unique electrical, magnetic or optical properties that stem from their chirality.     

Organocatalytic conversion of arylglyoxals into optically active mandelic acid derivatives

A novel protocol for the organocatalytic conversion of arylglyoxals into the corresponding α-hydroxy arylacetic acid methyl esters has been developed. The catalyst consists of a combination of a commercially available cinchona alkaloid derivative and an achiral thiol and leads to enantiomerically enriched products (ee_max 83%) under mild reaction conditions. The alkaloid can be easily recovered and reused without loss in activity and selectivity.     

Palladium complexes based on optically active terpene derivatives of ethylenediamine

Novel chiral palladium diamino complexes with the asymmetric donor N atom Pd(En*)X₂ (where En* = N,N′-bis{[(1S,5R)-6,6-dimethylbicyclo[3.1.1]hept-2-en-2-yl]methyl}-1,2-ethylenediamine; X = Cl and Br) were obtained and characterized. Nitrogen-containing derivatives of the natural monoterpene a-pinene were studied as accessible optically active ligands.     

Liquid-crystalline quinoline derivatives

A number of novel liquid crystals have been synthesized. 2-Phenylquinolines with alkyl or alkoxyl substituents in positions 6 and 4' show a texture typical of nematic mesophases and are characterized by a greater thermal stability than Schiff bases bearing the same substituents. The possibility of lowering the melting temperatures by means of eutectic mixtures is discussed.     

Chiral proton donor reagents: tin tetrachloride--coordinated optically active binaphthol derivatives

The Lewis acid–assisted chiral Brønsted acids (chiral LBAs), which are prepared from tin tetrachloride and optically active binaphthol derivatives, are highly effective chiral proton donor reagents for enantioselective protonation and biomimetic polyene cyclization. These chiral LBAs can directly protonate various silyl enol ethers and ketene disilyl acetals to give the corresponding α‐aryl or α‐halo ketones and α‐arylcarboxylic acids, respectively, with high enantiomeric excess (up to 98% ee). A catalytic version of enantioselective protonation was also achieved using stoichiometric amounts of 2,6‐dimethylphenol and catalytic amounts of monomethyl ether of optically active binaphthol in the presence of tin tetrachloride. The biomimetic cyclization of simple isoprenoids to polycyclic isoprenoids using chiral LBA is also described. This is the first example of a chiral Brønsted acid–induced enantioselective ene cyclization in synthetic chemistry. Geranyl phenyl ethers, o‐geranylphenols, and homogeranylphenol derivatives were directly cyclized in the presence of (R)‐binaphthol derivatives and tin tetrachloride (up to 90% ee). Compounds bearing a farnesyl group could also be cyclized under the same conditions to give the natural products (?)‐ambrox^® and (?)‐chromazonarol, and (?)‐tetracyclic polyprenoids of sedimentary origin. These chiral LBAs recognize the prochiral face of a trisubstituted terminal olefin and site selectively generate carbocations on the substrates. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2: 177–188,2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10020     

Two furo­pyridine complexes of nickel(II) iso­thio­cyanate

Pyridine fused with a furan ring (fupy), and its di­methyl derivative, have been used for the first time as ligands to synthesize potentially new Werner clathrates. The extended aromatic system of pyridine‐like ligands influences considerably the molecular structure of prepared nickel complexes. The molecular structure of tetrakis­(furo­[3,2‐c]­pyridine)­bis(iso­thio­cyanato)­nickel(II) tetra­hydro­furan (THF) solvate, [Ni(NCS)₂(C₇H₅NO)₄]·C₄H₈O or [Ni(NCS)₂(fupy)₄]·THF, (I), reveals a `four‐blade propeller' arrangement of ligands, with the angles between the fupy planes and the basal octahedron plane spanning the range 38.7–55.3°. These angles are much larger (69.9–78.8°) in the centrosymmetric complex tetrakis(2,3‐di­methyl­furo­[3,2‐c]­pyridine)­bis­(iso­thio­cyanato)nickel(II) 6.6‐hydrate, [Ni(NCS)₂(C₉H₉NO)₄]·6.6H₂O or [Ni(NCS)₂(Me₂fupy)₄]·6.6H₂O, (II), in which crystallographically imposed inversion symmetry is present.     

Synthesis of optically active trifluoromethylated indolizidine derivatives via stereoselective radical cyclization

[reaction: see text]. Asymmetric Michael reaction of lithiated trifluoroacetone SAMP-hydrazone with alkylidenemalonates gave addition products stereoselectively. Hydrolyzed enantiomerically pure ketoacids were cyclized to dihydropyridinones. N-Iodopropylation followed by radical cyclization gave optically active trifluoromethylated indolizidinones stereoselectively.     

Methylidyne tricobalt nonacarbonyl clusters; optically active silicon and germanium derivatives,and substitutions at silicon

The preparation and alcoholysis of chiral chlorosilanes containing the nonacarbonyltricobaltcarbon cluster, RR′Si(Cl)CCo₃(CO)₉, is described. The alkoxy derivatives react with i-Bu₂AlH or BF₃ · Et₂O to give the corresponding silicon hydride or fluoride. Reaction of methylidynetricobalt nonacarbonyl with optically active silanes of germane gave the optically active cluster complexes R¹R²R³M^*CCo₃(CO)₉ (M^* = Si, Ge). These compounds react with phosphine to give the monosubstituted R¹R²R³M^*CCo₃(CO)₈(PR₃ (M^* = Si, Ge). The diastereomers have been resolved in the case of the MePhSi (Obornyl) CCo₃(CO)₉ complex.     

Investigation of quinoline derivatives

The dehydrogenation of mononitro-1,2,3,4-tetrahydroquinolines and several of their N-acyl derivatives to the corresponding aminoquinolines was accomplished with various dehydrogenating agents. The maximum yields of aminoquino lines (15–20%) can be obtained when palladium on carbon is used as the dehydrogenating agent.See [1] for communication I.DeceasedTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 103—104, January, 1972     

Syntheses of quinoline derivatives

In order to study the relationship between structure and biological activity we have synthesized 5-alkoxymethyl- and 5-aryloxymethyl-7-bromo-8-quinolinols.For part II, see [1].     

Investigation of quinoline derivatives

Some dinitro derivatives of 1,2,3,4-tetrahydroquinoline and its N-acyl analogs were synthesized. The structures of the dinitro isomers obtained were confirmed by NMR, UV, and IR spectroscopic data.See [1] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 80–83, January, 1973.     

Enzymatic preparation of optically active 7-oxabicyclo[2.2.1] heptane derivatives

Enzymatic resolution of endo-7-oxabicyclo [2.2.1] hept-2-yl butyrates 3 and 5 using lipase from Candida cylindracea led to optically pure bicyclic alcohols and esters being important intermediates for the synthesis of biologically active compounds.     

Revisiting optically active quaternary derivatives made from prolinol as phase transfer catalysts

New non-racemic ammonium salts derived from prolinol have been prepared which are stereogenic both at N and at C. Absolute configurations rest on X-ray structures for 3c and 7a. The new compounds have been tested in a number of known enantioselective phase transfer catalytic (PTC) reactions to gain insight into steric control factors in such processes. Only very moderate e.e.s were observed. A SAMP hydrazone related catalyst (7a) reported by other authors was fully characterized. Racemic reaction products were obtained in two alkylations of diphenylmethylene benzylimine in the presence of this pure catalyst 7a. Very high e.e.s reported previously by others could not be reproduced.     

Circular dichroism of polyethylenimine containing optically active thymine derivatives as grafted pendants

Optical properties of linear polyethylenimine containing optically active (+)- or (?)-2-(thymin-1-yl)propionyl group as grafted pendant were investigated by circular dichroism (CD) and compared with those of the related monomer and dimer model compounds. CD spectra of the polymer in neutral aqueous solution were different from those of related model compounds, which suggest that the polymer exists in some ordered conformation (at least locally) to allow exciton coupling of π–π^* (B_2u) transition in the base chromophores along the polymer chain. This ordered conformation tends to be randomized on heating. The effects of complementary base pairing on the CD spectra have also been studied by using a linear polyethylenimine containing (±)-2-(adenin-9-yl) propionyl grafts and its related monomer and dimer models.     

Ferrocene derivatives, LXXI; Stereochemistry of metallocenes, LVI Synthesis and structure of optically active ferrocenylaminoalcohols

The reaction of enantiomerically pure 1,2-(-N,N-dimethylamino)-tetramethylene ferrocene (4) with butyllithium and subsequent treatment with either benzophenone or paraformaldehyde has yielded the aminoalcohols 6–11. The absolute configurations of 4 and 6–11 were deduced from the X-ray structures of the (R,R)-tartrate of 4 (4-T) and the aminoalcohol 6. In addition the optical purity of 4 was shown to be at least 95% by transformation into the ketone 2. In solution the annelated six-membered ring in compounds 4 and 6–11 was found to adopt a preferred half-chair conformation very similar to that found in the solid state structures of 4-T and 6.