Bicyclic Unit Research Articles

Methyl 12-Methyl-3,9-dinitro-5,6,7,12-tetrahydro-13-oxodibenzo[b.g]bicyclo[3.3.1]nonane-6-carboxylate and Related Compounds

A synthesis of the title compound and related structures is reported. The procedure involves double alkylation of a β-ketoester followed by double SNAr ring closure from the γ carbon to give a dibenzo[3.3.1]bicyclic unit. This paper appears to be the first to generate a mid-sized bicyclic target by a double SNAr process. The synthesis can be performed in one step, but yields are superior (52–62%) when a two-stage procedure is used.

A different polynorbornene backbone by combination of two polymer growth pathways: vinylic addition and ring opening via β-C elimination.

A new polynorbornene skeleton has been found that contains bicyclic norbornane units and cyclohexenyl methyl linkages. The polymers have been synthesized using a nickel catalyst in the presence of a controlled amount of ligands with low or moderate coordination ability. The backbone structure is the result of a vinylic addition polymerization, via sequential insertions of norbornene into a Ni–C bond (bicyclic units) combined with an unusual ring opening of the norbornene structure by a β-C elimination (cyclohexenyl methyl units) to give a new Ni–C(alkyl) bond that continues the polymerization. The ring opening events are favored when the rate of propagation of the vinylic addition polymerization decreases, and this can be modulated by making the coordination of norbornene to the metal center less favorable using additional ligands.

On free products inside the unit group of integral group rings

We use bicyclic units to give an explicit construction of a subgroup of isomorphic to the free product of two free abelian groups of rank two, assuming that G is a finite nilpotent group and it contains an element g of odd prime order such that the subgroup is not normal in G. To do this we first construct a subgroup isomorphic to the desired free product inside and then we find a nontrivial matrix representation of a subgroup of generated by some bicyclic units and their conjugations under the involution of We show that for an arbitrary finite group G our construction need not lead to a free product. At the end we shortly discuss possibility of constructing subgroups isomorphic to the free product of two free abelian groups of rank p − 1 for p > 3 in a similar way.

Soluble ethane-bridged silsesquioxane polymer by hydrolysis–condensation of bis(trimethoxysilyl)ethane: characterization and mixing in organic polymers

Gel structure of ethane-bridged trialkoxysilsesquioxane has been investigated extensively. In contrast, only a few studies have focused on the characterization of soluble ethane-bridged silsesquioxane polymer (sEBSP) because of difficult preparation and isolation processes. The present study aims to characterize the sEBSP and investigate its mixing effect in an organic polymer. The sEBSP was prepared by the hydrolysis–condensation of bis(trimethoxysilyl)ethane under a nitrogen flow and characterized by nuclear magnetic resonance spectroscopy (NMR), Fourier-transform infrared (FTIR) spectroscopy, and gel permeation chromatography (GPC). Based on the NMR and FTIR results, sEBSP was characterized as a randomly structured polymer with hybridized linear, cyclic, branched, and bicyclic units. It was mixed with poly(methyl methacrylate) (PMMA) and poly(bisphenol A-co-epichlorohydrin) (PBE) to form PMMA–sEBSP and PBE–sEBSP, respectively, which were then characterized by FTIR spectroscopy. The results confirmed the formation of hydrogen bonds between sEBSP and the organic polymer. The thermal stabilities of PMMA–sEBSP were better than those of the pure polymers. PBE–sEBSP exhibited a lower 5% weight loss temperature (Td5) because of the transalkoxylation between PBE and sEBSP. The miscibility of organic polymers and sEBSP was confirmed by differential scanning calorimetry (DSC). Based on their glass transition temperature, PMMA–sEBSP and PBE–sEBSP were classified as a hybrid and nanocomposite, respectively. Therefore, sEBSP was miscible to PMMA and PBE and affected to thermal properties.

Fast motion of molecular rotors in metal-organic framework struts at very low temperatures.

The solid state is typically not well suited to sustaining fast molecular motion, but in recent years a variety of molecular machines, switches and rotors have been successfully engineered within porous crystals and on surfaces. Here we show a fast-rotating molecular rotor within the bicyclopentane-dicarboxylate struts of a zinc-based metal-organic framework-the carboxylate groups anchored to the metal clusters act as an axle while the bicyclic unit is free to rotate. The three-fold bipyramidal symmetry of the rotator conflicts with the four-fold symmetry of the struts within the cubic crystal cell of the zinc metal-organic framework. This frustrates the formation of stable conformations, allowing for the continuous, unidirectional, hyperfast rotation of the bicyclic units with an energy barrier of 6.2 cal mol-1 and a high frequency persistent for several turns even at very low temperatures (1010 Hz below 2 K). Using zirconium instead of zinc led to a different metal cluster-carboxylate coordination arrangement in the resulting metal-organic framework, and much slower rotation of the bicyclic units.

Interlayer dielectrics based on copolyimides containing non-coplanar alicyclic-units for multilevel high-speed electronics

A series of copolyimides (CPIs) containing non-coplanar alicyclic units combined with fluorinated or rigid aromatic monomer segments is synthesized. The solid film samples display an elevated heat resistance as their degradation started at temperatures around 415 °C. Introduction into CPI backbone of bicyclic units, aromatic/aliphatic rings, angular bonds and/or low polarizable groups, determine the variation of the dielectric constant in the range 2.44–3.04 at 100 Hz. When using these CPIs as interlayer dielectrics (ILDs), it is revealed that resistance-capacitance delay is minimized (~10−11 s) determining faster response of the device. Atomic force microscopy scans of CPI samples show distinct macromolecular architectures, all containing nanopores with features depending on the chemical structure. Interfacial adhesion of investigated ILDs with copper wiring is highest for the samples lacking fluorine groups.

Stereoselective Synthesis of the A,E-Ring Bicyclic Core of Calyciphylline B-Type Alkaloids

A stereoselective synthesis of the bicyclic unit constituting the A and E rings of calyciphylline B-type alkaloids is disclosed. The propionate ester of (1R)-cyclohex-2-en-1-ol, obtained by enzymatic resolution, is subjected to an Ireland–Claisen rearrangement. Subsequent reduction of the acid, Mitsunobu reaction to introduce a nitrogen functionality, oxidative cleavage to a dialdehyde, and intramolecular aldol and aza-Michael reactions afford the bicyclic subunit.

Visible‐Light‐Promoted Polycyclizations of Dienynes

AbstractA variety of linear dienynes can deliver complex tetracyclic frameworks in the presence of an IrIII complex and visible light. Product formation involves the generation of four new C−C bonds and six contiguous stereocenters, which decorate two [3.1.0] bicyclic units tethered through their bridging quaternary carbon atoms. The internal alkyne acts as a formal dicarbenoid for the generation of two cyclopropanes in these radical cation cascades. This behavior has not been previously observed for organic reactive intermediates and can be extended to intermolecular reactions and diendiynes.

Visible-Light-Promoted Polycyclizations of Dienynes.

A variety of linear dienynes can deliver complex tetracyclic frameworks in the presence of an IrIII complex and visible light. Product formation involves the generation of four new C-C bonds and six contiguous stereocenters, which decorate two [3.1.0] bicyclic units tethered through their bridging quaternary carbon atoms. The internal alkyne acts as a formal dicarbenoid for the generation of two cyclopropanes in these radical cation cascades. This behavior has not been previously observed for organic reactive intermediates and can be extended to intermolecular reactions and diendiynes.

Amide nitrogen pyramidalization changes lactam amide spinning

Although cis-trans lactam amide rotation is fundamentally important, it has been little studied, except for a report on peptide-based lactams. Here, we find a consistent relationship between the lactam amide cis/trans ratios and the rotation rates between the trans and cis lactam amides upon the lactam chain length of the stapling side-chain of two 7-azabicyclo[2.2.1]heptane bicyclic units, linked through a non-planar amide bond. That is, as the chain length increased, the rotational rate of trans to cis lactam amide was decreased, and consequently the trans ratio was increased. This chain length-dependency of the lactam amide isomerization and our simulation studies support the idea that the present lactam amides can spin through 360 degrees as in open-chain amides, due to the occurrence of nitrogen pyramidalization. The tilting direction of the pyramidal amide nitrogen atom of the bicyclic systems is synchronized with the direction of the semicircle-rotation of the amide.

Synthesis of Fused Bicyclic [1,2,3]-Triazoles from γ-Amino Diazoketones

Triazoles are an important class of N-heterocycles that are well known for their broad biological activities. In this work, we would like to demonstrate a direct synthesis of the rare fused bicyclic [1,2,3]-triazoles, employing γ-N-protected amino diazoketones as useful synthetic platforms. The strategy was based on the deprotection of a trifluoroacetamide group for the intramolecular and in situ generation of an α-diazo imine intermediate, followed by a 5-endo-dig cyclization to construct the bicyclic unit. In this fashion, the synthesis of a series of fused bicyclic [1,2,3]-triazoles could be carried out in good to excellent yields (63–95%).

Synthesis of pyrrolizidines and indolizidines by multicomponent 1,3-dipolar cycloaddition of azomethine ylides

AbstractDifferent multicomponent 1,3-dipolar cycloadditions (1,3-DC) of cyclic α-amino acid derivatives with aldehydes and dipolarophiles have been described as efficient and simple methodologies for the synthesis of the pyrrolidine unit of pyrrolizidines and indolizidines. When free cyclic α-amino acids are used, a thermal promoted decarboxylative process generatesin situthe corresponding non-stabilized azomethine ylides, which afforded the corresponding pyrrolizidines and indolizidines with a hydrogen in the bicyclic units. This methodology has been employed to the synthesis of complex systems including spiro derivatives when ketones are used as carbonyl component. In addition, working with cyclic α-amino acid derived esters, the three-component 1,3-DC takes place under milder reaction conditions giving the corresponding pyrrolizidines and indolizidines with an alkoxycarbonyl group in the bridge adjacent carbon to the nitrogen. This methodology can be carried out by a double consecutive or stepwise 1,3-DC to provide pyrrolizidines via the precursor prolinates. The conformation of the azomethine ylide controls the endo/exo diastereoselectivity of the 1,3-DC.

Ethyl 3-amino-2-cyano-4-(4-methoxyphenyl)-6- methylthieno[2,3-b]pyridine-5-carboxylate

In the title molecule, C19H17N3O3S, the bicyclic core is planar [maximum deviation = 0.0205 (1) Å] In the crystal, the molecules stack along thea-axis direction through π–π-stacking interactions between the bicyclic units with a small alternation in the interplanar distances along the stack. The stacks are held together by N—H...N and C—H...O hydrogen bonds. The carboethoxy substituent is disordered over several closely spaced sites and was modeled as having two-component disorder [occupancy ratio 0.548 (16):0.452 (16)]. The final refinement was as a two-component twin.

Novel Multiblock Poly(ε-caprolactone) Copolyesters Containing D-Glucose Derivatives with Different Bicyclic Structures

For improving the thermal stability, glass transition temperature (Tg), stiffness, and hydrophilicity of poly(e-caprolactone) (PCL), two glucose-based bicyclic rigid structures, namely 1,4:3,6-dianhydrohexitols-D-glucidol (isosorbide, Is) and dimethyl 2,4:3,5-di-O-methylene-D-glucarate (glu-diester) have been introduced into PCL via chain extension. The two series of multiblock copolyesters obtained, PCL-b-PIS and PCL-b-PBG, have high number-average molecular weights in the range of 9.6 × 104 to 12.4 × 104 g mol–1 and small PDI values. The thermal and crystallization behaviors, hydrophilicity, as well as the mechanical properties of PCL-b-PIS and PCL-b-PBG have been well investigated. In comparison, the improved effect on thermal stability and Tg of PCL is more pronounced for PCL-b-PBG than for PCL-b-PIS. Both glucose-based units retard the crystallinity of PCL. However, the crystal structure and melting temperature of PCL remain unchanged. The rigidness of PCL is enhanced when glucose-based bicyclic unit...

Isohexide and Sorbitol-Derived, Enzymatically Synthesized Renewable Polyesters with Enhanced Tg.

Sugar-based polyesters derived from sorbitol and isohexides were obtained via solvent-free enzymatic catalysis. Pendant hydroxyl groups, coming from the sorbitol units, were present along the polyester backbone, whereas the two isohexides, namely, isomannide and isoidide dimethyl ester monomers, were selected to introduce rigidity into the polyester chains. The feasibility of incorporating isomannide as a diol compared to the isoidide dimethyl ester as acyl-donor via lipase-catalyzed polycondensation was investigated. The presence of bicyclic units resulted in enhanced Tg with respect to the parent sorbitol-containing polyester lacking isohexides. The different capability of the two isohexides to boost the thermal properties confirmed the more flexible character provided by the isoidide diester derivative. Solvent-borne coatings were prepared by cross-linking the sugar-based polyester polyols with polyisocyanates. The increased rigidity of the obtained sugar-based polyester polyols led to an enhancement in hardness of the resulting coatings.

Involutions and free pairs of bicyclic units in integral group rings of non-nilpotent groups

If ∗ : G → G is an involution on the finite group G, then ∗ extends to an involution on the integral group ring Z[G]. In this paper, we consider whether bicyclic units u ∈ Z[G] exist with the property that the group 〈u, u∗〉, generated by u and u∗, is free on the two generators. If this occurs, we say that (u, u∗) is a free bicyclic pair. It turns out that the existence of u depends strongly upon the structure of G and on the nature of the involution. The main result here is that if G is a non-nilpotent group, then for any involution, Z[G] contains a free bicyclic pair.

Bass units as free factors in integral group rings of simple groups

Let G be a finite group, u a Bass unit based on an element a of G of prime order, and assume that u has infinite order modulo the centre of the units of the integral group ring ZG. It was recently proved that if G is solvable then there is a Bass unit or a bicyclic unit v and a positive integer n such that the group generated by un and vn is a non-abelian free group. It has been conjectured that this holds for arbitrary groups G. To prove this conjecture it is enough to do it under the assumption that G is simple and a is a dihedral p-critical element in G. We first classify the simple groups with a dihedral p-critical element. They are all of the form PSL(2,q). We prove the conjecture for p=5; for p>5 and q even; and for p>5 and q+1=2p. We also provide a sufficient condition for the conjecture to hold for p>5 and q odd. With the help of computers we have verified the sufficient condition for all q<10000.

Mechanistic insight into highly efficient gas permeation and separation in a shape-persistent ladder polymer membrane

A fully atomistic simulation study is reported to provide mechanistic insight into the superior performance experimentally observed for a polymer membrane (Carta et al., Science, 2013, 339, 303-307). The membrane namely PIM-EA-TB is produced by a shape-persistent ladder polymer of intrinsic microporosity (PIM) with rigid bridged bicyclic ethanoanthracene (EA) and Tröger's base (TB). The simulation reveals that PIM-EA-TB possesses a larger surface area, a higher fraction free volume and a narrower distribution of torsional angles compared to PIM-SBI-TB, which consists of less rigid spirobisindane (SBI). The predicted surface areas of PIM-EA-TB and PIM-SBI-TB are 1168 and 746 m(2) g(-1), close to experimental values of 1120 and 745 m(2) g(-1), respectively. For five gases (CO2, CH4, O2, N2 and H2), the solubility and diffusion coefficients from simulation match well with experimental data, except for H2. The solubility coefficients decrease in the order of CO2 > CH4 > O2 > N2 > H2, while the diffusion coefficients increase following CH4 < CO2 < N2 < O2 < H2. In terms of the separation for CO2/N2, CO2/CH4 and O2/N2 gas pairs, PIM-EA-TB exhibits higher permselectivities than PIM-SBI-TA, in good agreement with experiment. From a microscopic perspective, this simulation study elucidates that the presence of bridged bicyclic units in PIM-EA-TB enhances the rigidity of polymer chains as well as the capability of gas permeation and separation, and the bottom-up insight could facilitate the rational design of new high-performance membranes.

UNITS IN F2D2p

Let p be an odd prime, D2pbe the dihedral group of order 2p, and F2be the finite field with two elements. If * denotes the canonical involution of the group algebra F2D2p, then bicyclic units are unitary units. In this note, we investigate the structure of the group [Formula: see text], generated by the bicyclic units of the group algebra F2D2p. Further, we obtain the structure of the unit group [Formula: see text] and the unitary subgroup [Formula: see text], and we prove that both [Formula: see text] and [Formula: see text] are normal subgroups of [Formula: see text].

Transformation of a Phosphorus-Bound Cp* Moiety in the Coordination Sphere of Manganese Carbonyl Complexes

The reaction of Cp*PCl2 with K[Mn(CO)5] yields two novel anionic products, [Mn2(CO)8(μ-PC11H14O)]− (1–) and [Mn2(CO)8(μ-PHCp*)]− (2–), instead of the expected phosphinidene complexes with a delocalized Mn–P–Mn bond system. By treating these anionic complexes with [Ph3PAuCl], they are converted into corresponding neutral derivatives [Mn2(CO)8(μ-PC11H14O)(μ-AuPPh3)] (3) and [Mn2(CO)8(μ-PHCp*)(μ-AuPPh3)] (4). NMR investigations and X-ray structural analyses for 1–, 3, and 4 show that the compounds 1– and 3 as well as 2– and 4 reveal similar molecular structures in which the neutral complexes 3 and 4 contain AuPPh3 units bridging Mn–Mn bonds. In comparison to 1 and 3, complexes 2 and 4 possess one additional H atom bound at the P atom. The structures of 1 and 3 include a novel bicyclic unit consisting of a C5 ring of the former Cp* moiety conjugated to a CCC(O)P four-membered ring. The latter is built by a CO group of a former Mn carbonyl fragment connecting a P and a C atom of the cycle. One of the methyl groups of the Cp* ligand became a CH2 unit, resulting in two isomers containing an exocyclic CH2 moiety in the positions three or five of the C5 ring. Both isomers were found in the reaction mixture, with one as the major isomer. The proposed reaction pathway is based on XRD, NMR, and MS data and includes the reduction of a transient [Cp*P(Mn(CO)5)2] complex by [Mn(CO)5]−, a proton transfer from the neutral to the reduced complex, and a successive reduction of the protonated species. The neutral bicyclic compound 3, containing a 2-phosphacyclobutanone ring, is light sensitive and decomposes to tetramethylfulvene, possibly by a radical decarbonylation mechanism via a transient phosphacyclobutane derivative, [C5(CH3)4(CH2)P(Mn(CO)4)2AuPPh3] (5), detected by NMR spectroscopy.