Volume 82, Issue 3

The 9th International Conference on Heteroatom Chemistry (ICHAC-9) was held in the Auditorio Príncipe Felipe of Oviedo, Spain, from 30 June to 4 July 2009. The conference was chaired by Prof. José Barluenga (University of Oviedo, Spain) and attracted about 210 participants, mainly organic and inorganic chemists, from 30 countries all around the world. The scientific program consisted of 9 plenary lectures, 21 invited lectures, 48 short communications, and 68 posters. This conference explored the state of the art of heteroatom chemistry and focused on the following major themes: - heteroatom ligands in catalysis - heteroatoms in organic (non-metal) catalysis - heteroatoms in medicine - heteroatom polymers and materials - heteroatom bonding and synthesis Besides the collection of 16 papers (based on plenary and invited lectures with the choice of oral contributions) included in this issue of Pure and Applied Chemistry , the ICHAC-9 Book of Abstracts remains available online and can be free downloaded from <http://www.uniovi.es/ichac9/> in pdf format. ICHAC will return to its origins for its 10th meeeting, and, therefore, ICHAC-10 will be held in Kyoto (Japan) in 2011 and will be hosted by Prof. Norihiro Tokitoh of Kyoto University. It is confidently expected that the conference will continue to fulfill its important scientific role in highlighting ongoing advances in heteroatom chemistry. The organizers are grateful to all who contributed to a successful scientific program, especially to the speakers and to our public and private sponsors: Ministerio de Ciencia e Innovación (Spain), Consejería de Educación y Ciencia del Principado de Asturias (by Plan de Ciencia, Tecnología e Innovación-PCTI Asturias), Ayuntamiento de Oviedo, Universidad de Oviedo, Fundación Universidad de Oviedo, Lilly, Bruker and Scharlab and the Organic Division of the Spanish Royal Society of Chemistry (Grupo Especializado en Química Orgánica de la RSEQ). Finally, in particular, we would like to thank all contributors to this issue for their timely efforts and the editorial staff for their help. Enrique Aguilar and Carlos Valdés Conference Editors

This paper describes the convenient method of isolating endohedral metallofullerenes by means of selective reduction from carbon soot extracts. Successful isolation in large amount by utilizing this method allows examination of the selective chemical modification of monometallofullerenes. Furthermore, isolation of missing metallofullerenes as their derivatives is also mentioned.

The search for molecular receptors capable of forming stable associates with fullerenes is a very active field of research in fullerene chemistry, with the purification from fullerite and the self-assembly of nanoscale electronic devices as driving forces. The construction of bivalent, tweezer-like receptors featuring two recognizing units connected through a spacer is one of the most successful design strategies employed in this field. Here, we present an overview of the most significant examples of these “molecular tweezers” for fullerenes.

Three different instrumental methods have been used to examine the organosulfur chemistry of intact and cut garlic and onions: X-ray fluorescence spectroscopic imaging (XFS), direct analysis in real time (DART) mass spec-trometry, and ultra-performance liquid chromatography-(Ag + )-coordination ion spray mass spectrometry (UPLC–(Ag + )CIS–MS). The first technique has been used to map the location of different chemical forms of sulfur in intact and damaged onion cells, the second technique, to identify the reactive, volatile sulfur compounds formed on cutting the plants, and the third technique, to identify members of families of polysulfides found in the distilled oil of garlic.

This review illustrates the ready availability of thioamide dianions and their versatility as carbon nucleophiles adjacent to the nitrogen atom. The products derived from the addition of thioamide dianions to a range of electrophiles can participate in a cyclization reaction to form nitrogen-containing heterocycles. The electronic properties of thioamide dianions are also considered.

The electrochemistry of m -terphenylthio-, seleno-, and telluroethers was studied using cyclic voltammetry in acetonitrile. All of the compounds studied showed irreversible oxidations. The first oxidation potentials for the thio- and selenoethers are less positive than expected. This facilitation in oxidation is ascribed to through-space S···π and Se···π inter-action, respectively, on removal of an electron. No evidence for a comparable effect was found for the phenyltelluro-ethers studied.

This account summarizes our recent results on transition-metal-catalyzed cleavage of C–Se bond and addition to unsaturated hydrocarbons such as alkynes and allenes. Pd(0)-catalyzed intramolecular carbamoselenation of alkynes forms four- to eight-membered α-alkylidenelactams. Interestingly, four-membered ring formation is faster than five- and six-membered ring formation. Intramolecular vinylselenation of suitably structured alkynes offers pathways to conjugated δ-lactam frameworks. Electron-withdrawing groups on the vinyl moiety are essential to promote this reaction. Intermolecular 1,2-addition of selenol esters onto allenes proceeds with excellent regioselectivity and high stereoselectivity in the presence of a Pd(0) catalyst, producing functionalized allyl selenides. In addition, Pd(0)-catalyzed intramolecular selenocarbamoylation of allenes gives α,β-unsaturated γ- and δ-lactams with perfect regioselectivity. The scope and limitations, as well as reaction pathways, are discussed.

New approaches to asymmetric synthesis of α-, β- and γ-aminophosphonic acids using enantiopure p -toluenesulfinimines as key reagents are reported. The utility of the devised methods is illustrated by the syntheses of enantiomeric aminophosphonic acids such as AP4, AP3, and its 3-amino isomer.

Our recent studies on the synthesis, structures, and aromaticity of phosphole-containing porphyrins and their metal complexes are summarized. Core-modified P,X,N 2 -porphyrins (X = S, N) are accessible from a σ 4 -phosphatripyrrane and the corresponding 2,5-difunctionalized heteroles in a few steps. X-ray structural analysis of the σ 3 -P,N 3 porphyrin revealed that it possesses a slightly distorted 18π plane. The phosphorus atom incorporated at the core plays an important role in producing unprecedented reactivity and coordinating ability for the porphyrin ring. The P,N 3 free base reacts with [RhCl(CO) 2 ] 2 in dichloromethane, ultimately yielding an 18π P,N 3 –rhodium(III) complex, whereas the P,S,N 2 free base undergoes redox-coupled complexation with zero valent group 10 metals to afford the corresponding P,S,N 2 -isophlorin–metal(II) complexes. The aromaticity of the free-base porphyrins and the metal complexes was uncovered based on both experimental and theoretical results. It is of particular interest that the P,S,N 2 -isophlorin–metal complexes exhibit only a weak antiaromaticity in terms of the magnetic criterion.

An account is given of our efforts in the synthesis of homo- and heterocyclic silanes via occasionally stable unsymmetrically substituted disilene intermediates of the A 2 Si=Si(A)B type that are accessible from a disila analog of a vinyl lithium. This approach is particularly powerful in the preparation of three-membered rings such as cyclotrisilanes with a residual functionality that can be either electro- or nucleophilic in nature and can even give rise to ring-expanded products with preserved Si=Si moiety. The intermediacy of transient silylenes in some of these transformations is discussed as well as the structural effects of the electronic properties of the residual functional group. The relevance of these studies for the understanding of Si(100) surface annealed species during the epitaxial growth of elemental silicon is pointed out, and the potential of the methodology for the synthesis of unusual polycyclic silicon clusters is noted.

A novel 1,2-diaryldisilyne, BbtSi≡SiBbt (Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl), was synthesized as a stable compound by reduction of the corresponding 1,2-dibromodisilene, Bbt(Br)Si=Si(Br)Bbt. The spectral and structural features of this first stable 1,2-diaryldisilyne are revealed, and the Si≡Si triple-bond character is evaluated with the aid of detailed theoretical calculations. The triple-bond characters of BbtSi≡SiBbt and BbtGe≡GeBbt are compared based on experimental and theoretical results.

A summary of recent advances in the chemistry and photophysics of alternating dialkylsilylene-divinylarene copolymers is presented. The silicon moieties are considered to be insulating tetrahedral spacers in these copolymers. The substituents on silicon can readily be tuned, and the steric environment of these substituents around the silicon may dictate the conformation (or helicity) of the copolymers (the Thorpe–Ingold effect) and hence their photophysical properties. Because different chromophores can be regioregularly introduced into the polymeric chain, these copolymers have been used as models to study energy transfer and photoinduced electron transfer (PET), as well as chiroptical transfer.

Electrophilic metal carbenoids, readily available from diazo compounds, prove to be good reagents for the preparation of ylides under neutral conditions. We have extended the strategy to synthesize allenes from diazoacetates with both stable and unstable ketenes in the presence of PPh 3 and Fe(TCP)Cl (0.5 mol %), which provided an easy access to optically active 4,4-disubstituted allenic esters by employing enantiopure phosphines. The mechanism involving the generation of ylide through catalytic transfer of an iron(II) carbene to phosphine was confirmed. A tandem Wittig–Nazarov cyclization reaction was further developed based on these results, culminating in a straightforward method for the construction of β-methylenecyclopentenones in a multistep one-pot manner without isolation of inter-mediates. By combining AsPh 3 and iron carbenoids, a catalytic Wittig reaction in toluene/water biphasic system was accomplished, affording α,β-unsaturated esters in high yields with E / Z above 50/1. Surprisingly, crotonate-derived phosphorus ylide reacted with electrophilic iron carbenoid, affording 1,1,4-trisubstituted 1,3-butadienes with high regio- and stereo-selectivities, where a new ylide generated via formal intermolecular carbenoid insertion into olefinic C–H bonds of the crotonate-derived phosphorus ylide was proposed.

Improved organometallic catalysts resulting from including ligands capable of proton transfer or hydrogen bonding are described. Pyridyl- and imidazolylphosphines accelerate anti -Markovnikov alkyne hydration and alkene isomerization and deuteration by factors of 1000 to more than 10 000. Evidence for proton transfer and hydrogen bonding in catalytic intermediates comes from computational, mechanistic, and structural studies, where 15 N NMR data are particularly revealing.

The tris(pyrazolyl)borate [HB(3,5-(CF 3 ) 2 Pz) 3 ] − prepared using highly fluorinated 3,5-bis(trifluoromethyl)pyrazole and BH 4 − is an excellent supporting ligand for the stabilization of a number of rare organometallic complexes of coinage metals. For example, it has enabled the isolation of Cu(I), Ag(I), and Au(I) complexes of CO and ethylene as crystalline solids. Syntheses, spectroscopic and structural features, and properties of [HB(3,5-(CF 3 ) 2 Pz) 3 ]ML (M = Cu, Ag, Au; L = CO, C 2 H 4 ) are the main focus of this discussion. Several metal adducts based on the tris(triazolyl)borate [HB(3,5-(CF 3 ) 2 Tz) 3 ] − supporting ligand as well as the cationic, coinage metal multi-alkene complexes containing the [SbF 6 ] − counterion are also discussed.

The selective synthesis of oxazoles, alkylidene oxazoles, and 1,3-oxazines from N -propargyl carboxamides by choosing gold(III) or gold(I) catalysts and selecting terminal or internal alkynes as substrates is discussed. The mechanistic studies based on labeling experiments and intensive in situ NMR studies indicate an anti -oxyauration step and a proto-deauration with retention of the sterical arrangement at the double bond. The synthetic scope for gold(I) catalysts is very broad, allowing selective conversions to products with properties of chelate ligands, reactions of bromoarenes and the formation of acceptor-substituted oxazoles. With N -heterocyclic carbene (NHC) ligands in the presence of a base, even the vinylgold intermediates of the reactions leading to 1,3-oxazines could be isolated, a reaction with a great potential for future mechanistic studies and future applications of gold catalysis.

The use of domino and multicomponent reactions in asymmetric synthesis is constantly increasing nowadays. This allows for the synthesis of complex molecules in a single synthetic sequence, usually with high atom economy. Herein, we report three examples of new asymmetric tandem reactions recently developed in our laboratories, giving rise to new families of enantiomerically enriched fluorinated and nonfluorinated heterocycles. Thus, 1,4-dihydropyridines (1,4-DHPs) bearing fluorinated substituents at C6 were assembled by means of a Hantzsch-type reaction; cyclic β-amino carbonyl derivatives were prepared using a cross-metathesis (CM)–intramolecular aza-Michael sequence; while fluorinated indolines were obtained, for the first time, in a tandem nucleophilic addition–intramolecular aromatic substitution.

The objective of the “Explanatory Dictionary of Key Terms in Toxicology” is to give full explanations of the meaning and usage of toxicological terms chosen for their importance and complexity with regard to the merging of chemistry into toxicology. This requires a full description of the underlying concepts, going beyond a normal dictionary definition. Often linguistic barriers lead to problems in obtaining a common understanding of terminology at an international level and between disciplines. The explanatory comments should help to break down such barriers. This dictionary is a follow-up and continuation of part I published in 2007. It consists of a collection of terms chosen from the IUPAC “Glossary of Terms Used in Toxicology”. These terms are organized under 19 main headings. The authors hope that this explanatory dictionary will be helpful to chemists, pharmacologists, toxicologists, risk assessors, regulators, medical practitioners, regulatory authorities, and everyone with an interest in the application of chemistry to solving toxicological problems. It should be of particular value to those involved in risk assessment and management.

A joint IUPAC/IUPAP Working Party (JWP) has confirmed the discovery of the element with atomic number 112. In accord with IUPAC procedures, the discoverers proposed a name, copernicium, and symbol, Cn, for the element. The IUPAC Inorganic Chemistry Division Committee recommended this proposal for acceptance, and it has now been approved by the IUPAC Bureau as delegated to act by the IUPAC Council meeting on 12 August 2007.