Search

Pyrido[3,2-b][1,4]oxazine and pyrido[2,3-b][1,4]benzoxazine systems were synthesised by annelation reactions involving highly fluorinated pyridine derivatives and nitrogen and oxygen centred difunctional nucleophiles by sequential regioselective nucleophilic aromatic substitution processes.

Review: current state of the art in low temperature and high pressure crystallography of molecular organic and coordination compounds; 50 refs.

Novel polyfluorinated imidazolopyrazine scaffolds (III) and (IX) are obtained in a one-step procedure from tetrafluoropyrazine (I).

The method includes three sequential reactions with nucleophiles as amines and sodium alkoxides.

In the presence of KF-Al2O3 and Pd(PPh3)4 highly fluorinated nitrobenzenes undergo efficient and regioselective coupling to new 2-nitrobiphenyl derivatives like (III) and (V).

Fluorinated diphenyl ether systems are synthesized starting from 1,2- and 1,3-dibromotetrafluorobenzene with high regioselectivity.

Hexachloronorbornadiene forms a 1 : 1 adduct 3 with 5,6-bismethylenenorbornene, which, on reaction with 1,2,3,4-tetrachlorothiophene dioxide, yields by loss of SO2, cycloreversion and further cycloaddition two compounds shown by mass, 13C NMR and 1H NMR spectroscopy and a single-crystal X-ray structure determination to be the isomeric products of a rare type of specific diene-capture by perchlorothiophene dioxide; a rational explanation for this and other examples is proposed, and a further example of norbornene sp2C pyramidalisation is disclosed.

The efficient synthesis of a range of novel 1,4,2-dithiazine derivatives by ring expansion of the corresponding 1,3-dithiolium cations in the presence of iodine and aqueous ammonia is reported; the eight π-electron 1,4,2-dithiazine ring is folded about the S ⋯ S axis, as shown by single crystal X-ray analysis, and the heterocycle is electrochemically oxidised to yield, sequentially, the radical cation and dication species.

A range of derivatives of the 8 π-electron 1,4,2-dithiazine system, viz. compounds 11a–d and 19–24, have been synthesised by ring expansion of the corresponding 1,3-dithiolium salts 8a–d and 13–18, respectively, using a mixture of iodine and aqueous ammonia at room temperature. A mechanism is proposed for the reaction. Competing reaction of compound 14 yields the imine 26 as a minor product. Single crystal X-ray analyses of compounds 11a and 23 reveal that the 1,4,2-dithiazine ring adopts a boat conformation with fold angles about the S ⋯ S axis of 50 and 48°, respectively. The 1,4,2-dithiazine heterocycle is oxidised electrochemically to yield the cation radical at E1½ca. 1.0–1.2 V (versus Ag/AgCl); some derivatives are further oxidised to the dication at E2oxca. 1.4–1.7 V.

The syntheses of four new gibberellin vicinal epoxy alcohols are described. The 1α-hydroxy 2β,3β-epoxides 3 and 9 were prepared in good yield from the corresponding ring A iodo diol 2 or 8via dehydrohalogenation followed by a Payne-type rearrangement. The structure of compound 3 was confirmed by X-ray crystallography. Although the 2β,3β-epoxide GA611 is a natural product, neither of the 1α-hydroxy derivatives was found to be naturally occurring.

The reaction of mono-lithiated tetrathiafulvalene (TTF) with elemental sulfur or elemental selenium at –78 °C yields the transient species TTF-S– Li+ and TTF-Se– Li+, respectively, which have been trapped with a range of alkyl halides to yield new alkylthio- and alkylseleno-TTF derivatives. Reaction of the TTF-thiolate anion with 2-bromoethanol yields 4-(2-hydroxyethylthio)tetrathiafulvalene which is a particularly versatile building block for the synthesis of a range of new mono-functionalised TTF derivatives containing ether, ester, acrylate, urethane and vinylthio groups in the side chain. Onepot syntheses of ethylenedithio-TTF (EDT-TTF) and ethylenediseleno-TTF (EDS-TTF) from TTF are reported. The structure of EDS-TTF has been determined by single crystal X-ray analysis which reveals dimers with molecular planes orthogonal to each other.

The unusual four coordinate bis(imido) alkene complexes [Mo(NBut)2(CH2CHR)(PMe3)](R = H, Me) have been synthesised via treatment of [Mo(NBut)2Cl2(dme)](dme = dimethoxyethane) with two equivalents of RCH2CH2MgCl (R = H, Me) in the presence of PMe3; the molecular structure of the propene derivative is reported.

The synthesis and solution redox properties of several covalently attached ferrocene and tetrathiafulvalene units are reported, together with the X-ray crystal structure of a 1,1′-bis(1,3-dithiole-2-ylidene)-substituted ferrocene derivative.

DBU 1 reacts as a (1,3) difunctional nucleophile with 2-H heptafluorobut-2-ene 2, giving the unusual product 8; a mechanism for the formation of 8 is proposed and an X-ray crystal structure of 8 is described.

Strong intramolecular charge-transfer which occurs in fluorenes 2 and 3 from the donor amino group(s) to the acceptor fluorene moiety leading to exceptionally easy rotation around the C(9)C(α) bond has been observed in solution by 1H NMR and UV–VIS spectroscopy; single crystal X-ray analysis of compound 2h shows significant π-bond delocalization along the C(9)–C(14)–N(2) fragment.

An efficient one-step procedure is described for the synthesis of 2-(trifluoromethyl)butyrolactone 1 and 4-substituted 2-(trifluoromethyl)butyrolactones by the photocatalytic conjugate addition of primary and secondary alcohols to 2-(trifluoromethyl)acrylic acid 6. With the exception of methanol, the reactions are conducted without a photosensitiser. The diastereoisomers of compounds 8 and 10 were separable by chromatography and their relative configurations were established unambiguously by X-ray analyses of suitable crystals.

Benzoaza-15-crown-5 ethers containing one or two nitrogen atoms in different positions of the macrocycle and bearing different substituents at these atoms were synthesized. The structures of azacrown ethers and their metal complexes were studied by X-ray diffraction. The stability constants of the complexes of azacrown ethers with Na+, Ca2+, Ba2+, Ag+, Pb2+, and EtNH3+ ions were determined by 1H NMR titration in MeCN-d3. In free benzoazacrown ethers containing secondary nitrogen atoms bound to the benzene ring, as well as in N-acetyl derivatives, the N atoms are sp2-hybridized and have a planar geometry. The nitrogen lone pairs on the p orbitals are efficiently conjugated to the benzene ring or the carbonyl fragment of the acetyl group, which is unfavorable for the complex formation. In addition, the formation of complexes with benzoazacrown ethers containing secondary nitrogen atoms is hindered because the hydrogen atoms of the NH groups are directed to the center of the macrocyclic cavity. In benzoazacrown ethers bearing N-alkyl substituents or secondary nitrogen atoms distant from the benzene ring, the N atoms show a substantial contribution of the sp3-hybridized state and have a pronounced pyramidal configuration, which promotes the complex formation. The lead and calcium cations form the most stable complexes due to the high affinity of Pb2+ ions for O,N-containing ligands, a high charge density on these ions, and the better correspondence of the cavity size of the 15-membered macrocycles to the diameter of the Ca2+ ion. An increase in the stability of the complexes is observed mainly in going from monoazacrown ethers to diazacrown ethers containing identical substituents at the N atoms and in the following series of substituents: C(O)Me < H < Me < CH2CO2Et. In the case of the CH2CO2Et substituents, the carbonyl oxygen atom is also involved in the coordination to the cation. The characteristic features of the complexing ability of N-alkylbenzomonoaza-15-crown-5 ethers bearing the nitrogen atom conjugated to the benzene ring show that macro-cyclic ligands having this structure are promising as selective and efficient complexing agents for metal cations.

Syntheses of the acenaphtho[1,2-b][1,4]dithiine derivatives 12, 25 and 29 are reported. Cyclic voltammetric studies reveal that these compounds undergo reversible single-electron oxidations at < 1.0 V, vs. Ag/AgCl. Lithiation of compound 12 with BuLi (2 equiv.) followed by addition of either methyl iodide or ethyl chloroformate yielded the unstable ring-opened acetylene derivatives 22a and 22b, respectively. A new synthesis of 1,2-diselenine derivative 33 is reported. Compound 25 formed 1 : 1 charge-transfer complexes with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and with 2,5-dibromo-TCNQ, both of which were electrical insulators. The X-ray crystal structures of compound 25, a charge-transfer complex 25:Br2TCNQ (1:1 stoichiometry) and compound 33 are reported. In the structure of 25:Br2TCNQ, molecules of 25 and Br2TCNQ form mixed stacks. The folding of the donor along the S ⋯ S vector in the complex is 17°(cf. 48° in pure 25) and the conformation of 25 is discussed in the light of previous studies on 1,4-dithiine derivatives. An interesting feature of the crystal structure of 33 is the formation of pseudo-dimers with two short intermolecular Se ⋯ Se contacts.

The reaction of 5,6-dimethyl-3-(4-bromophenyl)-1,4,2-dithiazine 1b with dimethyl acetylenedicarboxylate (DMAD) at 180 °C in o-dichlorobenzene affords a mixture of thiophene derivative 5 and isothiazole derivative 6: the former probably via the zwitterionic adduct 3 and dithiine derivative 4, neither of which are isolable; the latter by sulfur extrusion from 1b. Reaction of norbornene with 1b affords dithiine derivative 7. Oxidation of 1b with meta-chloroperoxybenzoic acid yields the 1,1-dioxide derivative 8, the X-ray crystal structure of which is reported. The efficient synthesis of 3-aryl-6-methylthio-1,4,2,5-dithiadiazine derivatives 12a–c by ring expansion of 1,4,2-dithiazolium salts 11a–c with an iodine–ammonia reagent is described. Reaction of 12c with DMAD at 180 °C affords the stable dithiine derivative 14, probably via the intermediate 1,4,2-dithiazine 13. Electrochemical oxidation of 12a–c is irreversible, yielding 1,4,2,5-dithiadiazinium cation radicals at potentials [E ox = 1.55–1.73 V (vs. Ag/AgCl)] which are sensitive to the electronic nature of the para-substituent on the aryl ring. The X-ray crystal structure of 12b is reported.

A three step stereoselective route to the fluorinated natural product (2S,3S)-4-fluorothreonine is described; the route is amenable to the preparation of (2S,3S)-4-fluoro[3- 2 H]threonine and (2S,3R)-[4,4,4- 2 H 3 ]threonine.

The synthesis of 1,4-dithiafulvene-substituted ferrocene derivatives 7, 11 and 12 by reaction of formyl-, diformyl- and diacetyl-ferrocene, respectively, with the carbanion generated from reagents 4a–c and the ylide prepared from reagent 5 is reported. Upon reaction with HCl–diethyl ether, compounds 7a–c undergo an oxidative dimerisation to yield extended tetrathiafulvalene (TTF) derivatives 8a–c. The solution electrochemistry of compounds 7, 8, 11, 12, 14 and 16 has been studied by cyclic voltammetry. The X-ray crystal structures of compounds 8b and 12a are presented.

Reaction between hydroxylamine (1) and ethyl trifluoromethylacetoacetate (2) is reported. A crystal structure of the resultant isoxazolidin-3-one (3) was obtained.

Ferrocene derivatives 1, 2a, 2b and 5 act as electrochemical sensors of Mg2+ and Ca2+ ions in acetonitrile solution in concentrations as low as 10 mol%: a new redox peak appears in the cyclic voltammogram, anodically shifted by 160–360 mV, with no interference from a large excess of several other metal salts; the single crystal X-ray structure of ligand 5 is reported.

The solid-state 199Hg MAS NMR spectra of [Hg(SCN)2], [Hg(SeCN)2], M[Hg(SCN)3], M2[Hg(SCN)4] (M = K, Cs), and K2[Hg3(NCO)8] have been measured, and the (monoclinic) crystal structure of [Hg(SeCN)2] has been determined to assist in the interpretation of the NMR data. The asymmetric unit of Hg(SeCN)2 contains one molecule at an inversion center which shows linear Se−Hg−Se bonding (Hg−Se = 2.4738(10) A, Se−Hg−Se = 180°, Hg−Se−C = 97.5(3)°). Secondary Hg---Se and Hg---N contacts are 3.4246(9) and 2.835(12) A, respectively; this arrangement differs from that in Hg(SCN)2 where there are no secondary Hg---S contacts. A redetermination of the monoclinic crystal structure of K[Hg(SCN)3] is also reported, revealing substantial differences from the earlier work. Spinning sideband analysis has been used to determine the 199Hg shielding anisotropy and asymmetry parameters Δσ and η from the solid-state 199Hg MAS NMR spectra. The effects of changes in the mercury coordination number and of distortion of the coordination ...

Pentafluorophenol reacts with sodium trichloroacetate in monoglyme in a Reimer-Tiemann reaction to give not only pentafluorophenyl orthoformate (6) but also a previously unknown ‘abnormal’ type of product, tetrakis(pentafluorophenoxy)ethene (5). one possible formation of which could be by dimerisation of an intermediate carbene.

New 1,3-dithiol-2-ylidene derivatives, notably π-extended systems, have been synthesised by Wittig reactions of phosphorane and phosphonate ester derivatives of 1,3-dithiole with activated ketones and α,β-unsaturated ketones. Nitrosation reactions of a range of these π-extended systems, results in the formation of nitroalkenes, via unstable nitrosoalkene intermediates, which, in general, could not be isolated. The X-ray crystal structure of 1-(4,5-dicarbomethoxy-1,3-dithiol-2-ylidene)-1-cyano-1-phenyl-methane reveals a small degree of intramolecular electron transfer from the dithiole ring to the conjugated cyano group.