Spatial effects in polymer chemistry

• Helmut Ritter

Beilstein J. Org. Chem. 2017, 13, 2015–2016, doi:10.3762/bjoc.13.198

• tacticity of a polymeric chain is a result of spatial interactions between the active growing chain end and the free monomer or a monomer–metal complex. Moreover, the preferred head-to-tail chain growth of vinyl monomers can be a result of such spatial effects. The spatial arrangement of polymer chains in

Mechanochemical synthesis of thioureas, ureas and guanidines

• Vjekoslav Štrukil

Beilstein J. Org. Chem. 2017, 13, 1828–1849, doi:10.3762/bjoc.13.178

• : corrugated chains of head-to-head or head-to-tail aligned molecules and discrete centrosymmetric dimers based on the R22(8) supramolecular synthon in the case of sterically hindered thioureas (Figure 2). The crystal structures of N,N'-diarylthioureas linked in chains via N–H···S hydrogen bonds can further be

Pd(OAc)₂/Ph₃P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

• Dominik Kellner,
• Maximilian Weger,
• Andrea Gini and
• Olga García Mancheño

Beilstein J. Org. Chem. 2017, 13, 1807–1815, doi:10.3762/bjoc.13.175

• formed: tail-to-tail, head-to-tail, tail-to-head and head-to-head (Figure 1). In addition to the linear dimeric products, cyclic monoterpenes such as limonene can also be formed as byproducts. A number of transition metal complexes can be used as catalysts in the dimerization of isoprene. In one hand

• the tail-to-tail linkage [15][29]. Moreover, the naturally occurring head-to-tail 2-HT dimers, myrcene and ocimene, can be obtained in allylic alcohol when employing Pd(NO3)2/Ph3P/KOPh as catalytic system [30]. The head-to-head 2-HH dimer could also be prepared as major isomer under catalysis with the

A new member of the fusaricidin family – structure elucidation and synthesis of fusaricidin E

• Marcel Reimann,
• Louis P. Sandjo,
• Luis Antelo,
• Eckhard Thines,
• Isabella Siepe and
• Till Opatz

Beilstein J. Org. Chem. 2017, 13, 1430–1438, doi:10.3762/bjoc.13.140

• -resin head-to-tail macrolactamization instead [11]. A similar strategy had been used by Cudic and co-workers to synthesize analogs of fusaricidin A with an on resin coupling of a 12-aminododecanoic acid combined with a late stage guanidinylation to give the unnatural 12-guanidinyldodecanoic acid side

Opportunities and challenges for the sustainable production of structurally complex diterpenoids in recombinant microbial systems

• Katarina Kemper,
• Max Hirte,
• Markus Reinbold,
• Monika Fuchs and
• Thomas Brück

Beilstein J. Org. Chem. 2017, 13, 845–854, doi:10.3762/bjoc.13.85

• the comparably short chains of dolichols [39]. The vast majority of terpenes, steroids and other isoprenoids like cholesterols and carotenoids are obtained from E-condensations [35]. Head-to-tail connection of single IPP and DMAPP by geranyl diphosphate synthase (GPPS) results in geranyl diphosphate

Polyketide stereocontrol: a study in chemical biology

• Kira J. Weissman

Beilstein J. Org. Chem. 2017, 13, 348–371, doi:10.3762/bjoc.13.39

• synthases (PKSs), in a process resembling fatty acid biosynthesis by the mammalian fatty acid synthase (FAS) [8] from which the PKSs likely evolved [9]. In both cases, simple acyl-CoA building blocks are concatenated head-to-tail to construct linear chains. Several features distinguish these two pathways

A new class of organogelators based on triphenylmethyl derivatives of primary alcohols: hydrophobic interactions alone can mediate gelation

• Wangkhem P. Singh and
• Rajkumar S. Singh

Beilstein J. Org. Chem. 2017, 13, 138–149, doi:10.3762/bjoc.13.17

• gelator molecules may be arranged linearly in a head-to-tail (end-to-end) direction. These linear arrays can then interact laterally with two triphenylmethyl groups in close proximity to neighbouring octyl chains resulting in a roughly two-dimensional planar packing arrangement. The distance between any

Radical polymerization by a supramolecular catalyst: cyclodextrin with a RAFT reagent

• Kohei Koyanagi,
• Yoshinori Takashima,
• Takashi Nakamura,
• Hiroyasu Yamaguchi and
• Akira Harada

Beilstein J. Org. Chem. 2016, 12, 2495–2502, doi:10.3762/bjoc.12.244

• condensed phase. Figure 2a shows the crystal structure of α-CD with DMA. α-CD formed a head-to-tail channel structure in the crystal. Figure 2b shows the schematic diagram of the crystal structure of α-CD/DMA. The stoichiometry of α-CD and encapsulated DMA was 1:1. The N,N-dimethylamino group was located at

Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

• ETH A7796 as well as by Streptomyces fulvissimus and consists of four nonactic acid units, which are assembled in a head-to-tail fashion giving a C2-symmetric (−)-(+)-(−)-(+) macrocycle [53]. Nonactin (70) biosynthesis has been extensively studied and shows multiple unusual features. Genes of an ACP

Cyclisation mechanisms in the biosynthesis of ribosomally synthesised and post-translationally modified peptides

• Andrew W. Truman

Beilstein J. Org. Chem. 2016, 12, 1250–1268, doi:10.3762/bjoc.12.120

• elimination step. Macrolactam and macrolactone formation A diverse array of macrolactams are found in RiPPs from bacteria [31], plants [83] and mammals [84]. These can arise from a variety of routes: (i) head-to-tail cyclisation by attack of the N-terminal amine of the core peptide onto the C-terminus [85

• identified [87][90]. The most well-studied member of the family is microcin J25 (Figure 7C) from E. coli AY25. Initial structural characterisation incorrectly identified microcin J25 as a conventional head-to-tail macrocyclic peptide [91], which was later revised to the lassoed structure by multiple groups

• formed by the head-to-tail cyclisation of two nonapeptides that are themselves derived from the C-terminal region of precursor peptides, and both heterodimers or homodimers can be formed in this process [84][144]. Along with their antimicrobial activity, these peptides can inhibit fusion of HIV-1 to host

Bi- and trinuclear copper(I) complexes of 1,2,3-triazole-tethered NHC ligands: synthesis, structure, and catalytic properties

• Shaojin Gu,
• Jiehao Du,
• Jingjing Huang,
• Huan Xia,
• Ling Yang,
• Weilin Xu and
• Chunxin Lu

Beilstein J. Org. Chem. 2016, 12, 863–873, doi:10.3762/bjoc.12.85

• environment of two nitrogen atoms and two oxyen atoms. The Cu–O bonds are in trans configuration and Cu–O distances are shorter than Cu–N distances. The two ligands are arranged in head-to-tail manner. And the Ntriazole did not participate in the corrdination. Single crystals of complex 3 suitable for an X

• two L2 ligands. The two ligands are arranged in head-to-tail manner. The copper ions are each tri-coordinated by one carbene carbon atom, one nitrogen from pyrimidine, and one nitrogen atom of the triazole rings from two different L2 ligands. The Cu–carbene bond distances are 1.896(6) and 1.899(5) Å

• . Complex 4 crystallizes in the triclinic space group P-1. The two ligands are also arranged in head-to-tail manner. Each copper ion is three-coordinate in a trigonal planar ligand environment of two nitrogen atoms and one NHC carbon center. The Cu–carbene bond distances are 1.888(6) and 1.899(5) Å which

Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes

• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 117–124, doi:10.3762/bjoc.12.13

• isomers of complex [M(cod){µ-C3H2N2(Mes)-κC2,κN3}]2). The latter two isomers display conformations head-to-head (H-H) and head-to-tail (H-T) of CS and C2 symmetry, respectively. The isomerization from the H-H to the H-T conformation is feasible, whereas next substitutions of the cod ligand by CO first

• , and PMe3 later confirm the H-T coordination as the thermodynamically preferred. It is envisaged the exchange of the metal, from iridium to rhodium, confirming here the innocence of the nature of the metal for such arrangements of the bridging ligands. Keywords: DFT; head-to-head; head-to-tail

• 3H-H and 3H-T (where H-H = head-to-head and H-T = head-to-tail). By DFT calculations here we contribute in the understanding of the thermodynamics of the subsequent C,N-bridged dinuclear iridium and rhodium complexes [59], and the facility for the interconversion between these latter dimeric species

Star-shaped tetrathiafulvalene oligomers towards the construction of conducting supramolecular assembly

• Masahiko Iyoda and
• Masashi Hasegawa

Beilstein J. Org. Chem. 2015, 11, 1596–1613, doi:10.3762/bjoc.11.175

• . The intramolecular through-bond interaction between the two TTF parts linked in a head-to-tail manner is calculated to be weak in the ground state [25]. Thus, the conjugation of the two neutral TTF parts in 16–19 is weak (Figure 6) [59]. In the cyclic voltammetry (CV) measurements, tetraethylthio-bi

• , from the corresponding absorption maximum of 16•+, 17•+, and 18•+ due to the head-to-tail orientation of two TTF•+ (Davydov red shift) [25]. It is worth noting that the redox behavior of TTF dimers in CV measurements are sensitive to the concentration and the solvent used, and pristine bi-TTF 15b

Synthesis of racemic and chiral BEDT-TTF derivatives possessing hydroxy groups and their achiral and chiral charge transfer complexes

• Sara J. Krivickas,
• Chiho Hashimoto,
• Junya Yoshida,
• Akira Ueda,
• Kazuyuki Takahashi,
• John D. Wallis and
• Hatsumi Mori

Beilstein J. Org. Chem. 2015, 11, 1561–1569, doi:10.3762/bjoc.11.172

• the usual θ11-type has the +−+−+−... pattern [23]. In every (+) and (−)-stacking column, the alternate (R,R)–(S,S)–(R,R)–(S,S)- chiral donors indicated by blue–red–blue–red are stacked such as C’AC’A..., A’CA’C..., or BB’BB’... in head-to-tail fashion (Figure 2b). Moreover, the molecules with the same

• are four donors, two anions, and two H2O solvents in the unit cell. The enantiopure (R,R)-2 donors stack in a head-to-tail manner and twisted with respect to each other along the a-axis, namely the α’-type donor arrangement [25]. The hydroxymethyl groups project from the molecular BEDT-TTF plane in

Tetrathiafulvalene-based azine ligands for anion and metal cation coordination

• Awatef Ayadi,
• Aziz El Alamy,
• Olivier Alévêque,
• Magali Allain,
• Nabil Zouari,
• Mohammed Bouachrine and
• Abdelkrim El-Ghayoury

Beilstein J. Org. Chem. 2015, 11, 1379–1391, doi:10.3762/bjoc.11.149

• acceptor unit forming head-to-tail dimers. Moreover, the plane-to-plane distance between the donor and acceptor moieties is d = 3.39 Å, showing an evident overlap that is comparable to the reported intermolecular charge-transfer complexes [35]. This overlap develops along a-axis forming infinite columns

• (Figure 2). These columns are linked together along c-axis through hydrogen bonding occurring between TTF-C-H and NO2 (TTF-C–H1···O3-NO 2.493(6) Å). In the b-direction, the columns of stacked head to tail molecules are connected laterally through S···O heteroatom contacts (d = 3.16 Å, Figure S1

• : 794.8787; found: 794.8781. Crystal structure of ligand L1 with atom numbering scheme (top) and a side view of the molecule (bottom). Partial crystal packing of ligand L1 with formation of head to tail dimers that stack along a-axis forming columns that are connected through hydrogen bonding along c-axis

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

Regioselective synthesis of chiral dimethyl-bis(ethylenedithio)tetrathiafulvalene sulfones

• Flavia Pop and
• Narcis Avarvari

Beilstein J. Org. Chem. 2015, 11, 1105–1111, doi:10.3762/bjoc.11.124

• lengths range between 1.395(5) and 1.435(5) Å, while the central C5=C6 bonds have the same value of 1.347(7) Å for both A and B molecules, typical for neutral donors (Table 1). (S,S)-1 packs in pseudo-centrosymmetric head-to-tail dimers which are orthogonally disposed in an edge-to-face arrangement

Glycoluril–tetrathiafulvalene molecular clips: on the influence of electronic and spatial properties for binding neutral accepting guests

• Yoann Cotelle,
• Marie Hardouin-Lerouge,
• Stéphanie Legoupy,
• Olivier Alévêque,
• Eric Levillain and
• Piétrick Hudhomme

Beilstein J. Org. Chem. 2015, 11, 1023–1036, doi:10.3762/bjoc.11.115

• appeared in a head-to-tail arrangement and short TTF···TTF intermolecular distances (3.51 Å) were determined between two clips in the solid state. Binding properties In order to establish the influence of electronic and spatial properties of the clips towards binding ability of neutral electrodeficient

Synthesis and characterization of the cyanobenzene-ethylenedithio-TTF donor

• Sandrina Oliveira,
• Dulce Belo,
• Isabel C. Santos,
• Sandra Rabaça and
• Manuel Almeida

Beilstein J. Org. Chem. 2015, 11, 951–956, doi:10.3762/bjoc.11.106

• crystal structure is made by piling up molecules head to head forming stacks along the b axis (Figure 2) with short S–H contacts (S1–H1B; S4–H2B) in the range 2.751–2.824 Å. Neighbouring stacks are arranged head to tail in the a,c plane with several short contacts between molecules in neighbouring stacks

Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores

• Huixin Jiang,
• Virginia Mazzanti,
• Christian R. Parker,
• Søren Lindbæk Broman,
• Jens Heide Wallberg,
• Karol Lušpai,
• Adam Brincko,
• Henrik G. Kjaergaard,
• Anders Kadziola,
• Peter Rapta,
• Ole Hammerich and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104

• correspond to Davydov redshifts of head-to-tail TTF•+–TTF•+, signalling intramolecular interactions rather than face-to-face intermolecular interactions [2][30]. Additionally, although all investigated TTF dimers show quite analogous electrochemical and UV–vis–NIR spectroelectrochemical response, the EPR

• difficult to make unambiguous assignments of these to intra- and/or intermolecular mixed valence transitions. It is noteworthy, however, that the dications (TTF•+–TTF•+) experienced Davydov redshifts rather than blueshifts, which signal intramolecular head-to-tail interactions rather than face-to-face π

TTFs nonsymmetrically fused with alkylthiophenic moieties

• Rafaela A. L. Silva,
• Bruno J. C. Vieira,
• Marta M. Andrade,
• Isabel C. Santos,
• Sandra Rabaça,
• Dulce Belo and
• Manuel Almeida

Beilstein J. Org. Chem. 2015, 11, 628–637, doi:10.3762/bjoc.11.71

• -by-side chains of neutral α-tbtdt molecules. Within the chain the molecules are arranged head-to-tail, in a fashion that the cyanoethyl groups point outside the chain and the mean plane of neighbouring molecules is rotated by about 62°. The molecules are connected by several short S…S contacts

Synthesis and chemosensing properties of cinnoline-containing poly(arylene ethynylene)s

• Natalia A. Danilkina,
• Petr S. Vlasov,
• Semen M. Vodianik,
• Andrey A. Kruchinin,
• Yuri G. Vlasov and
• Irina A. Balova

Beilstein J. Org. Chem. 2015, 11, 373–384, doi:10.3762/bjoc.11.43

• of cinnoline units in both oligomer chains is not regular. Thus there are three types of hydroquinone spacers between head-to-head (red), tail-to-tail (blue) and head-to-tail (orange–purple) oriented cinnoline units in the irregular PAEs chains (Figure 5). Moreover for the hydroquinone moiety that

• connects head-to-tail oriented cinnoline units (orange–purple) the additional splitting was observed (for zoom copies of NMR spectra see Supporting Information File 2). Optical properties and metal-sensing ability of cinnoline-containing PAEs The absorption spectrum in the UV–vis range of THF solutions of

Inclusion of trans-resveratrol in methylated cyclodextrins: synthesis and solid-state structures

• Lee Trollope,
• Dyanne L. Cruickshank,
• Terence Noonan,
• Susan A. Bourne,
• Milena Sorrenti,
• Laura Catenacci and
• Mino R. Caira

Beilstein J. Org. Chem. 2014, 10, 3136–3151, doi:10.3762/bjoc.10.331

• packing is shown in Figure 7. The complex units pack in a head-to-tail manner in columns parallel to the crystal b-axis. Columns of complex units A propagate as rows parallel to the a-axis, alternating with analogous columns of B complex units. Structural analysis of the inclusion complex between

• parallel to the a-axis in a head-to-tail fashion (Figure 11a), adjacent columns being related by the two-fold screw axis along 1/2, y, 1/2. The view down the columns (Figure 11b) reveals a channel-like arrangement of the host molecules in this direction. Among the various isostructural classes of CD

• as well as numerous water–water O–H···O hydrogen bonds. The crystal packing is shown in Figure 15. Complex units stack in columns parallel to the a-axis in a head-to-tail fashion with (as noted above) a small extent of host self-inclusion (Figure 15a). Figure 15b illustrates the modified herringbone

Macrocyclic bis(ureas) as ligands for anion complexation

• Claudia Kretschmer,
• Gertrud Dittmann and
• Johannes Beck

Beilstein J. Org. Chem. 2014, 10, 1834–1839, doi:10.3762/bjoc.10.193

• head-to-tail arrangement with short intramolecular hydrogen bridges. An even stronger tilting of the molecule is expected for 2. Here, the distances are too large for any intramolecular N−H∙∙∙O bridging bonds. As a strong anion complexing agent 2 binds halide anions even in DMSO as solvent, despite

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50