Terminal Allyl Research Articles

Electron‐Assisted Deposition‐Polymerization in Vacuum of Polymethines with Terminal Allyl Group

AbstractPolymethines containing an allyl group have been synthesized. Their films are produced by physical vapor deposition (PVD) on glass, silicon (Si), gold (Au), polytetrafluoroethylene (PTFE), and nanostructured plastic substrates. Optical spectra recorded during the deposition showed no decomposition of molecules. The influence of dye structure and substrate on the morphology of the deposits is studied using atomic force microscopy (AFM). Depending on the dye structure and the substrate material, various nanostructures are grown. Dichroic nanowires (NWs) are formed by self‐assembly on Au and Si substrates. On the Si surface, NWs grow between the edges of neighboring Au stripes. Several methods are used for the selective opening of the allyl group. Smooth films are produced with optical spectra similar to those deposited by PVD. The morphology of the films is dependent on the activation conditions. The thermal stability of the films exceeds the stability of those deposited via PVD.

Polaronic Mechanism of Vibronic Localization in Mixed-Valence Cation Radicals with a Non-Conjugated Chromophore on the Bridge

In quest of a controllable intramolecular electron transfer (ET) across a bridge, we study the cation-radical form of the parent 1,4-diallyl-butane (I) and its derivatives (II)-(VI). In these mixed-valence (MV) compounds, the bridge of variable length connecting allyl redox sites can be either saturated (-CH2 CH2-) (I, III, and V) or unsaturated, modified by the π-spacer (-HC═CH-) (II, IV, and VI). Ab initio calculations for the charge delocalized transition structure and for fully optimized localized form of 1,ω-diallyl cation radicals I-VI allowed us to estimate the potential barriers for ET between the terminal allyl groups, vibronic coupling, and ET parameters. The ET barrier in all compounds with the π-fragment on the bridge is shown to be higher with respect to that in the systems with a saturated bridge. We propose a model based on the concept of a specific polaronic effect of the spacer. Charge localization at an allyl group creates an electric field polarizing the π-fragment and the bridge as a whole. The induced dipole moment interacts with the localized charge giving rise to the additional vibronic stabilization in a self-consistent manner without an appreciable change of localized charge. Utilization of this spacer-driven polaronic effect is expected to provide a route to a controllable ET in bridged MV compounds.

4-(All-yloxy)benzohydrazide.

The non-H atoms of the title compound, C10H12N2O2, are approximately coplanar with the exception of those at the ends: the terminal allyl carbon atom and terminal hydrazide nitro-gen atom are displaced from the mean plane by 0.67 (2) and 0.20 (2) Å, respectively. In the crystal, the mol-ecules are linked by N-H⋯O and N-H⋯N hydrogen bonds, which give rise a two-dimensional network propagating in the (001) plane.

Cooperative Catalyst-Enabled Regio- and Stereodivergent Synthesis of α-Quaternary α-Amino Acids via Asymmetric Allylic Alkylation of Aldimine Esters with Racemic Allylic Alcohols.

We describe cooperative bimetallic catalysis that enables regio-/stereodivergent asymmetric α-allylations of aldimine esters. By employing Et3 B as the key activator, racemic allylic alcohols can be directly ionized to form Pd or Ir-π-allyl species in the presence of achiral Pd or chiral Ir complexes, respectively. The less or more substituted allylic termini of the metal-π-allyl species are amenable to nucleophilic attack by the chiral Cu-azomethine ylide, the formation of which is simultaneously facilitated by Et3 B, affording α-quaternary α-amino acids with high regioselectivity and excellent stereoselectivity. The use of readily available allylic alcohols as electrophilic precursors represents an improvement from an environmental and atom/step economy perspective. Computational mechanistic studies reveal the crucial role of the Et3 B additive and the origins of stereo- and regioselectivities by analyzing steric effects, dispersion interactions, and frontier orbital population.

Cooperative Catalyst‐Enabled Regio‐ and Stereodivergent Synthesis of α‐Quaternary α‐Amino Acids via Asymmetric Allylic Alkylation of Aldimine Esters with Racemic Allylic Alcohols

AbstractWe describe cooperative bimetallic catalysis that enables regio‐/stereodivergent asymmetric α‐allylations of aldimine esters. By employing Et3B as the key activator, racemic allylic alcohols can be directly ionized to form Pd or Ir‐π‐allyl species in the presence of achiral Pd or chiral Ir complexes, respectively. The less or more substituted allylic termini of the metal‐π‐allyl species are amenable to nucleophilic attack by the chiral Cu‐azomethine ylide, the formation of which is simultaneously facilitated by Et3B, affording α‐quaternary α‐amino acids with high regioselectivity and excellent stereoselectivity. The use of readily available allylic alcohols as electrophilic precursors represents an improvement from an environmental and atom/step economy perspective. Computational mechanistic studies reveal the crucial role of the Et3B additive and the origins of stereo‐ and regioselectivities by analyzing steric effects, dispersion interactions, and frontier orbital population.

Kinetic, ESI-CID-MS and Computational Studies of π-Allyliridium C,O-Benzoate-Catalyzed Allylic Amination: Understanding the Effect of Cesium Ion.

The mechanism of π-allyliridium C,O-benzoate-catalyzed allylic amination was studied by (a) reaction progress kinetic analysis (RPKA), (b) tandem ESI-MS analysis, and (c) computational studies involving density functional theory (DFT) calculations. Reaction progress kinetic analysis (RPKA) reveals a zero-order dependence on allyl acetate, first-order dependence on catalyst and fractional-order dependence on amine. These data corroborate rapid ionization of the allylic acetate followed by turnover limiting C-N bond formation. To illuminate the origins of the 0.4 kinetic order dependence on amine, ESI-MS analyses of quaternary ammonium-labelled piperazine with multistage collision induced dissociation (CID) were conducted that corroborate intervention of cesium-bridged amine dimers that dissociate to form monomeric cesium amide nucleophiles. Computational data align with RPKA and ESI-CID-MS analyses and suggest early transition states mitigate the impact of steric factors, thus enabling formation of highly substituted C-N bonds with complete levels of branched regioselectivity. Specifically, trans-effects of the iridium complex facilitate nucleophilic attack at the more substituted allyl terminus trans to phosphorus with enantioselectivity governed by steric repulsions between the chiral bisphosphine ligand and the π-allyl of a dominant diastereomer of the stereogenic-at-metal complex. Beyond defining aspects of the mechanism of π-allyliridium C,O-benzoate-catalyzed allylic amination, these data reveal that a key feature of cesium carbonate not only lies in its enhanced basicity, but also its capacity for Lewis-acid enhanced Brønsted acidification of amines.

A Dipolar Cyclization/Fragmentation Strategy for the Catalytic Asymmetric Synthesis of Chiral Eight-Membered Lactams

A Dipolar Cyclization/Fragmentation Strategy for the Catalytic Asymmetric Synthesis of Chiral Eight-Membered Lactams

Synthesis of Ajoene Analogues by Novel Synthetic Strategies.

Ajoene is a compound found in garlic extracts exhibiting a large range of biological activity. Novel ajoene analogues have been prepared in the search of compounds with superior bioactivity. Modifications include the alteration of the sulfoxide, the central alkene and the terminal allyl groups.

An η3‐Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex

AbstractMilling two equivalents of K[1,3‐(SiMe3)2C3H3] (=K[A′]) with MgX2 (X=Cl, Br) produces the allyl complex [K2MgA′4] (1). Crystals grown from toluene are of the solvated species [((η6‐tol)K)2MgA′4] ([1⋅2(tol)]), a trimetallic monomer with both bridging and terminal (η1) allyl ligands. When recrystallized from hexanes, the unsolvated 1 forms a 2D coordination polymer, in which the Mg is surrounded by three allyl ligands. The C−C bond lengths differ by only 0.028 Å, indicating virtually complete electron delocalization. This is an unprecedented coordination mode for an allyl ligand bound to Mg. DFT calculations indicate that in isolation, an η3‐allyl configuration on Mg is energetically preferred over the η1‐ (σ‐bonded) arrangement, but the Mg must be in a low coordination environment for it to be experimentally realized. Methyl methacrylate is effectively polymerized by 1, with activities that are comparable to K[A′] and greater than the homometallic magnesium complex [{MgA′2}2].

An η3 -Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex.

Milling two equivalents of K[1,3-(SiMe3 )2 C3 H3 ] (=K[A']) with MgX2 (X=Cl, Br) produces the allyl complex [K2 MgA'4 ] (1). Crystals grown from toluene are of the solvated species [((η6 -tol)K)2 MgA'4 ] ([1⋅2(tol)]), a trimetallic monomer with both bridging and terminal (η1 ) allyl ligands. When recrystallized from hexanes, the unsolvated 1 forms a 2D coordination polymer, in which the Mg is surrounded by three allyl ligands. The C-C bond lengths differ by only 0.028 Å, indicating virtually complete electron delocalization. This is an unprecedented coordination mode for an allyl ligand bound to Mg. DFT calculations indicate that in isolation, an η3 -allyl configuration on Mg is energetically preferred over the η1 - (σ-bonded) arrangement, but the Mg must be in a low coordination environment for it to be experimentally realized. Methyl methacrylate is effectively polymerized by 1, with activities that are comparable to K[A'] and greater than the homometallic magnesium complex [{MgA'2 }2 ].

Synthesis, characterization and end-functionalization of a novel telechelic star: styrene hexamer core carrying polyisobutylene arms fitted with allyl termini

The synthesis and characterization of a new star consisting of a hard styrene hexamer (St6) core of which emanate long soft polyisobutylene (PIB) arms and fitted with allyl (A) termini is documented. The synthesis was accomplished by a core-first strategy in two steps: (a) creating the core by living anionic hexamerization of 3-(2-methoxyisopropyl)styrene in essentially quantitative conversion with nearly targeted molar mass (Mn = 1450 g/mol) of very low dispersity (1.06), and (b) using this hexamer to produce in one pot PIB-A arms by living cationic polymerization of isobutylene (> 99% conversion), and terminating with allyltrimethylsilane. This is the first example of a star synthesis by anionic-to-cationic site transformation. Intermediates and final products were characterized by 1H NMR spectroscopy and GPC according to which the star had ~ 4.61 arms. The star was end-functionalized by thiol-ene clicking with furfuryl mercaptan (~ 85% yield) for the preparation of a furan-telechelic star.

Reductive C-O, C-N, and C-S Cleavage by a Zirconium Catalyzed Hydrometalation/β-Elimination Approach.

A zirconium catalyzed reductive cleavage of Csp3 and Csp2 carbon-heteroatom bonds is reported that makes use of a tethered alkene functionality as a traceless directing group. The reaction is successfully demonstrated on C-O, C-N, and C-S bonds and proposed to proceed via a hydrozirconation/β-heteroatom elimination sequence of an in situ formed zirconium hydride catalyst. The positional isomerization of the catalyst further enables the cleavage of homoallylic ethers and the removal of terminal allyl and propargyl groups.

Preparation of multi-allylic dendronized polymers via atom-transfer radical polymerization

Atom-transfer radical polymerization (ATRP) was investigated to polymerize a styrene monomer carrying carbosilane dendrons with 6 terminal allyl branches. Polymers with a monomodal molar mass distribution and low polydispersity have been produced, while by comparison the free-radical polymerization technique led to chain transfer early in the polymerization. Steric effect brought by the dendrons result in a slow polymerization rate, leading to an apparent saturation of the degree of polymerization. By pushing up the polymerization conditions (eg. increase of temperature or concentration), interchain couplings started to take place, most likely from reactions at the allyl branches. These results are very similar to the ones previously reported for the anionic polymerization of this same multi-allylic dendronized monomer.

Oligodeoxynucleosides with Olefin Bridges

The synthesis and self-assembly studies of DNA/RNA-mimic artificial polymers have drawn extensive scientific attention since synthetic chemists can manipulate the functions of these modified nucleic acid molecules by varying their macromolecular backbone and nucleoside unit structures. In this paper, we report two types of modified nucleic acids with olefin bridges prepared by acyclic diene metathesis polymerization (ADMET). The 3′-OH and 5′-OH groups of deoxythymidine and deoxyadenosine analogue monomers are functionalized with either two terminal allyl units or allyl and acryloyl units, respectively. The consequent ADMET approaches provide either regio-uncontrolled oligodeoxynucleosides with poor E/Z selectivity or well-defined oligodeoxynucleosides built in a highly ordered head-to-tail addition manner. These two different macromolecular structures markedly influence the self-assembly morphologies of the corresponding oligodeoxynucleosides, which show spherical and filamentous helix nanostructures, respectively.

'Beta version' of neuroplasticity or absolute beta power in preterm infants as electroencephalographic correlate of synaptogenesis

Although numerous Schiff base complexes have been synthesized and characterized, reports on Schiff base ligands and complexes derived from amines containing terminal allyl group are rare. In this work, four halogenated Schiff base compounds were synthesized by reaction of halogenated salicylaldehydes (3,5-dichlorosalicylaldehyde, 3,5-dibromosalicylaldehyde, 3,5-diiodosalicylaldehyde and 3-bromo-5-chlorosalicylaldehyde) with allyl amine in water as green solvent at ambient temperature and characterized by elemental analyses, NMR (1H and 13C), and FT-IR spectroscopy. In continue, their Cu(II) complexes were synthesized and characterized by elemental analyses, FT-IR and single-crystal X-ray diffraction. All complexes show halogen-halogen, π–π, CH–π interactions and also metal–halogen secondary bonds in crystal packing. The coordination geometry around the Cu(II) in all reported compounds is best described as square planar with two axially elongated interactions named metal–halogen secondary bond (Cu…X), all beyond the sum of the corresponding vdW radii (3.421 Å for Cu…Cl in (Cl2L)2Cu, 3.463 Å for Cu…Br in (Br2L)2Cu, 3.486 Å for Cu…I in (I2L)2Cu and 3.467 Å for Cu…Cl in (BrClL)2Cu). The crystal structures have also been subjected to Hirshfeld surface analysis which reveals that approximately most of the close contacts correspond to relatively weak interactions. Also, all of the interactions in crystal packing have been analyzed by theoretical calculations.

Enantioselective Synthesis of Tertiary Allylic Fluorides by Iridium‐Catalyzed Allylic Fluoroalkylation

AbstractFew allylic electrophiles containing two different substituents at a single allyl terminus and none in which one of the two substituents is a heteroatom, have been shown previously to react with iridium catalysts to form substitution products. We report that iridium‐catalysts are uniquely suited to form tertiary allylic fluorides enantioselectively by the addition of a diverse range of carbon‐centered nucleophiles at the fluorine‐containing terminus of 3‐fluoro‐substituted allylic esters. The products contain tertiary stereogenic centers bearing a single fluorine, which are isosteric with common tertiary stereocenters containing a single hydrogen. Computational studies reveal the principal steric interactions influencing the stability of endo and exo π‐allyl intermediates formed from 3,3‐disubstituted allylic electrophiles.

A close insight into the nature of intra- and intermolecular interactions in new Cu(II) Schiff base complexes derived from halogenated salicylaldehydes and allylamine: Theoretical and crystallographic studies

Although numerous Schiff base complexes have been synthesized and characterized, reports on Schiff base ligands and complexes derived from amines containing terminal allyl group are rare. In this work, four halogenated Schiff base compounds were synthesized by reaction of halogenated salicylaldehydes (3,5-dichlorosalicylaldehyde, 3,5-dibromosalicylaldehyde, 3,5-diiodosalicylaldehyde and 3-bromo-5-chlorosalicylaldehyde) with allyl amine in water as green solvent at ambient temperature and characterized by elemental analyses, NMR (1H and 13C), and FT-IR spectroscopy. In continue, their Cu(II) complexes were synthesized and characterized by elemental analyses, FT-IR and single-crystal X-ray diffraction. All complexes show halogen-halogen, π–π, CH–π interactions and also metal–halogen secondary bonds in crystal packing. The coordination geometry around the Cu(II) in all reported compounds is best described as square planar with two axially elongated interactions named metal–halogen secondary bond (Cu…X), all beyond the sum of the corresponding vdW radii (3.421 Å for Cu…Cl in (Cl2L)2Cu, 3.463 Å for Cu…Br in (Br2L)2Cu, 3.486 Å for Cu…I in (I2L)2Cu and 3.467 Å for Cu…Cl in (BrClL)2Cu). The crystal structures have also been subjected to Hirshfeld surface analysis which reveals that approximately most of the close contacts correspond to relatively weak interactions. Also, all of the interactions in crystal packing have been analyzed by theoretical calculations.

Electrophilic and nucleophilic addition reactions of Ir(1-2,5-η-CH2CHCHCHSO2)(PMe3)3 with HBF4, acetonitrile, CO, pyridine and methanol: Haptotropic behavior of the butadienesulfonyl ligand

Reaction of IrCl(PMe3)3 with one equivalent of K(SO2CHCHCHCH2) led to the formation of Ir(1-2,5-η-CH2CHCHCHSO2)(PMe3)3 (1). The reaction of 1 with HBF4⋅Et2O takes place rapidly at low temperature to give the metallacycle [Ir(2,5-η-MeCHCHCHSO2)(PMe3)3]BF4 (2). Complex 2 reacts with CH3CN, CD3CN and CO to give the corresponding adducts [Ir(2,5-η-MeCHCHCHSO2)(PMe3)3(L)]BF4 (L = CH3CN, 3; CD3CN, 3D; CO, 4). Interestingly, compound 2 in the presence of pyridine or deuterated pyridine isomerizes to the terminal allyl compound [Ir(1-3,5-η-CH2CHCHCH2SO2)(PMe3)3]BF4 (5), while in the presence of oxygenated solvents, such as methanol, acetone and water, or their corresponding deuterated solvents, affords a mixture of cationic internal allyl isomers [Ir(2-4,6-η-MeCHCHCHSO2)(PMe3)3]BF4 (6a) and [Ir(2-4,5-η-MeCHCHCHSO2)(PMe3)3]BF4 (6b), being 6a always the major isomer. The iridium center is coordinated to an oxygen atom of the sulfone moiety in 6a, while for 6b coordination through the sulfur atom is proposed. Single-crystal X-ray diffraction studies of 5 and 6a confirm the unprecedented formation of novel sulfone-pentenyl ligands bonded to the iridium center through an η3 interaction and also by S and O coordination affording six-membered pseudo-ring structures. The mechanism of the formation of 5 and the mixture of isomers 6a and 6b is discussed. A comparative study with the thiapentadienyl analogue Ir(1-2,5-η-CH2CHCHCHS)(PMe3)3 (1S) is also considered.

NHC-Copper-Catalyzed Tandem Hydrocupration and Allylation of Alkenyl Boronates

A tandem hydrocupration/allylation of alkenyl boronates efficiently proceeds with NHC-copper catalysts using hydrosilane and allyl phosphate as reagents. In the presence of IMes–Cu catalyst, the allylation of in situ generated Β-α-copper intermediates smoothly occurs to give homoallylic boronates in high yields, despite competitive side reaction pathways. Mono- and disubstituted alkenyl boronates were effective in the reaction with terminal allyl phosphates, but trisubstituted substrates showed limited reactivity.

Predictive Bioinformatic Assignment of Methyl-Bearing Stereocenters, Total Synthesis, and an Additional Molecular Target of Ajudazol B.

Full details on the evaluation and application of an easily feasible and generally useful method for configurational assignments of isolated methyl-bearing stereocenters are reported. The analytical tool relies on a bioinformatic gene cluster analysis and utilizes a predictive enoylreductase alignment, and its feasibility was demonstrated by the full stereochemical determination of the ajudazols, highly potent inhibitors of the mitochondrial respiratory chain. Furthermore, a full account of our strategies and tactics that culminated in the total synthesis of ajudazol B, the most potent and least abundant of these structurally unique class of myxobacterial natural products, is presented. Key features include an application of an asymmetric ortholithiation strategy for synthesis of the characteristic anti-configured hydroxyisochromanone core bearing three contiguous stereocenters, a modular oxazole formation, a flexible cross-metathesis approach for terminal allyl amide synthesis, and a late-stage Z,Z-selective Suzuki coupling. This total synthesis unambiguously proves the correct stereochemistry, which was further corroborated by comparison with reisolated natural material. Finally, 5-lipoxygenase was discovered as an additional molecular target of ajudazol B. Activities against this clinically validated key enzyme of the biosynthesis of proinflammatory leukotrienes were in the range of the approved drug zileuton, which further underlines the biological importance of this unique natural product.