Synthesis of Levulinic Acids From Muconic Acids in Hot Water.

Levulinic acid is a key biorenewable platform molecule. Its current chemical production from sugars is plagued by limited yields, char formation and difficult separations. An alternative and selective route starting from muconic acid via simple heating in water at high temperature (180 °C) has been developed. Muconic acid can be obtained from sugars or catechol fermentation. Chemical oxidation of catechol is another possibility which advantageously can also be applied on substituted catechols, hereby providing substituted muconic acids. When applying the disclosed hydrothermal protocol on these substrates hitherto unknown substituted levulinic acids were accessed. In particular, 3-propyllevulinic acid has been synthesized from 4-propylcatechol, prepared from pine wood. This propylated derivative has been used for the synthesis of a 3-propyllevulinate diester, i.e. butane-1,4-diyl bis(4-oxo-3-propylpentanoate), via esterification with 1,4-butanediol. The diester showed superior performance as plasticizer in comparison to the corresponding levulinate diester in both PVC (polyvinyl chloride) and PLA (polylactic acid). It plasticizes equally effective as the notorious commercial phthalate-based benchmark DEHP (di-2-ethylhexyl phthalate) in PVC.

Polarization attractors driven by vector soliton rain.

Soliton rain is a bunch of small soliton pulses slowly drifting near the main pulse having the period of a round trip. For Er-doped fiber laser mode-locked by carbon nanotubes, for the first time, we demonstrate both experimentally and theoretically a new type of polarization attractors controllable by vector soliton rain. With adjusting the pump power, vector soliton rain takes the form of pulses with rotating states of polarization which enable transforming slowly evolving trajectories on the Poincaré sphere from the double-scroll spiral to the circle. The obtained results on controlling complex multisoliton dynamics can be of interest in laser physics and engineering with potential applications in spectroscopy, metrology, and biomedical diagnostics.

Selective Nickel-Catalyzed Hydrodeacetoxylation of Aryl Acetates.

Acetate serves as a renewable and easily installed leaving group for selective deoxygenation of phenolics (ArOH). Ni-catalyzed hydrodeacetoxylation of aryl acetates (Ar-OAc) with HBpin in a green carbonate solvent selectively delivers the corresponding deoxygenated arenes (ArH). The method is also applicable to highly challenging guaiacyl and syringyl acetates, leaving -OMe groups intact without arene reduction. Renewable 4-propylguaiacol obtained from pine can also be transformed without significant loss in yield versus oil derived feedstock. The observed chemoselectivity for Ar-OAc versus ArO-Ac bond cleavage was rationalized based on mechanistic experiments and DFT calculations. ArOH side-product formation is attributed to direct competitive Ni-catalyzed reduction of the C=O bond. Hydrodeacyloxylation of a set of aryl alkanoates featured interesting chemoselectivity with a dramatic influence of the length and structure of the alkyl chain on catalysis.

Brønsted Acid Catalyzed Tandem Defunctionalization of Biorenewable Ferulic acid and Derivates into Bio-Catechol.

An efficient conversion of biorenewable ferulic acid into bio-catechol has been developed. The transformation comprises two consecutive defunctionalizations of the substrate, that is, C-O (demethylation) and C-C (de-2-carboxyvinylation) bond cleavage, occurring in one step. The process only requires heating of ferulic acid with HCl (or H2 SO4 ) as catalyst in pressurized hot water (250 °C, 50 bar N2 ). The versatility is shown on a variety of other (biorenewable) substrates yielding up to 84 % di- (catechol, resorcinol, hydroquinone) and trihydroxybenzenes (pyrogallol, hydroxyquinol), in most cases just requiring simple extraction as work-up.

Fiber echo state network analogue for high-bandwidth dual-quadrature signal processing.

All-optical platforms for recurrent neural networks can offer higher computational speed and energy efficiency. To produce a major advance in comparison with currently available digital signal processing methods, the new system would need to have high bandwidth and operate both signal quadratures (power and phase). Here we propose a fiber echo state network analogue (FESNA) - the first optical technology that provides both high (beyond previous limits) bandwidth and dual-quadrature signal processing. We demonstrate applicability of the designed system for prediction tasks and for the mitigation of distortions in optical communication systems with multilevel dual-quadrature encoded signals.

Isolator-free switchable uni- and bidirectional hybrid mode-locked erbium-doped fiber laser.

An Erbium-doped fibre ring laser hybrid mode-locked with single-wall carbon nanotubes (SWNT) and nonlinear polarisation evolution (NPE) without an optical isolator has been investigated for various cavity conditions. Precise control of the state of polarisation (SOP) in the cavity ensures different losses for counter-propagating optical fields. As the result, the laser operates in quasi-unidirectional regime in both clockwise (CW) and counter-clockwise (CCW) directions with the emission strengths difference of the directions of 22 dB. Furthermore, by adjusting the net birefringence in the cavity, the laser can operate in a bidirectional generation. In this case, a laser pumped with 75 mW power at 980 nm generates almost identical 790 and 570 fs soliton pulses with an average power of 1.17 and 1.11 mW. The operation stability and pulse quality of the soliton pulses in both unidirectional regimes are highly competitive with those generated in conventional ring fibre lasers with isolator in the cavity. Demonstrated bidirectional laser operation can find vital applications in gyroscopes or precision rotation sensing technologies.

Vector self-pulsing in erbium-doped fiber lasers.

Insight into instabilities of fiber laser regimes leading to complex self-pulsing operations is an opportunity to unlock the high power and dynamic operation tunability of lasers. Though many models have been suggested, there is no complete covering of self-pulsing complexity observed experimentally. Here, I further generalized our previous vector model of erbium-doped fiber laser and, for the first time, to the best of my knowledge, map tunability of complex vector self-pulsing on Poincare sphere (limit cycles and double scroll polarization attractors) for laser parameters, e.g., power, ellipticity of the pump wave, and in-cavity birefringence. Analysis validated by extensive numerical simulations demonstrates good correspondence to the experimental results on complex self-pulsing regimes obtained by many authors during the last 20 years.

Stereochemistry of the Brivaracetam Diastereoisomers.

The stereochemistry of all four stereoisomers of brivaracetam was determined using vibrational circular dichroism (VCD) spectroscopy. By comparing experimentally obtained VCD spectra and computationally simulated ones, the absolute configurations can be confidently assigned without prior knowledge of their relative stereochemistry. Neither the corrected mean absolute errors analysis of the nuclear magnetic resonance (NMR) data, nor the matching of experimental and calculated infrared spectra allowed the diastereoisomers to be distinguished. VCD spectroscopy itself suffices to establish the absolute configurations of all diastereoisomers. The relative stereochemistry could also be statistically confirmed by matching experimental and computed NMR spectra using the CP3 algorithm. The combination of VCD and NMR is recommended for molecules bearing more than one chiral center, as the relative configurations obtained from NMR serve as an independent check for those established with VCD. Analysis of the calculated VCD spectra reveals that the localized NH2 scissoring mode at around 1600 cm(-1) is characteristic for intramolecular hydrogen bonding, while the orientation of the ethyl group is reflected by the delocalized modes between 1150 and 1050 cm(-1).

Polarization attractors in harmonic mode-locked fiber laser.

We report on a polarimetry of harmonic mode-locked erbium-doped fiber laser with carbon nanotubes saturable absorber. We find new types of vector solitons with locked, switching and precessing states of polarization. The underlying physics presents interplay between birefringence of a laser cavity created by polarization controller along with light induced anisotropy caused by polarization hole burning.

Phase noise tolerance study in coherent optical circular QAM transmissions with Viterbi-Viterbi carrier phase estimation.

We present a performance evaluation of a non-conventional approach to implement phase noise tolerant optical systems with multilevel modulation formats. The performance of normalized Viterbi-Viterbi carrier phase estimation (V-V CPE) is investigated in detail for circular m-level quadrature amplitude modulation (C-mQAM) signals. The intrinsic property of C-mQAM constellation points with a uniform phase separation allows a straightforward employment of V-V CPE without the need to adapt constellation. Compared with conventional feed-forward CPE for square QAM signals, the simulated results show an enhanced tolerance of linewidth symbol duration product (ΔνTs) at a low sensitivity penalty by using feed-forward CPE structure with C-mQAM. This scheme can be easily upgraded to higher order modulations without inducing considerable complexity.

Study of EEPN mitigation using modified RF pilot and Viterbi-Viterbi based phase noise compensation.

We propose--as a modification of the optical (RF) pilot scheme--a balanced phase modulation between two polarizations of the optical signal in order to generate correlated equalization enhanced phase noise (EEPN) contributions in the two polarizations. The method is applicable for n-level PSK system. The EEPN can be compensated, the carrier phase extracted and the nPSK signal regenerated by complex conjugation and multiplication in the receiver. The method is tested by system simulations in a single channel QPSK system at 56 Gb/s system rate. It is found that the conjugation and multiplication scheme in the Rx can mitigate the EEPN to within ½ orders of magnitude. Results are compared to using the Viterbi-Viterbi algorithm to mitigate the EEPN. The latter method improves the sensitivity more than two orders of magnitude. Important novel insight into the statistical properties of EEPN is identified and discussed in the paper.

Bound state vector solitons with locked and precessing states of polarization.

We report experimental observation of new tightly and loosely bound state vector solitons with locked and precessing states of polarization in a carbon nanotube mode locked fiber laser in the anomalous dispersion regime.

Single-shot dynamics of dual-comb generation in a polarization-multiplexing fiber laser.

Dual optical frequency combs have been a recurrent case of study over the last decade due to their wide use in a variety of metrology applications. Utilizing a single cavity laser to generate a dual comb reduces system complexity and facilitates suppression of common noise. However, a dual-comb regime in single cavity lasers tends to be more unstable and difficult to achieve. Therefore, having a better understanding about the way they are generated could improve and automate their generation and control. In this paper, we investigate the build-up dynamics and collision of dual comb in a polarization-multiplexing ring-cavity fiber laser using DFT (Dispersive Fourier Transform) method. We observe a bunch of meta-stable short-lived mode-locking states before the laser entered the dual-comb mode-locking state. The energy level of this short-lived initial pulses determines its evolution. If it decreases too much, the pulse will eventually collapse while if it stays above certain level, it will be successfully generated. The results presented in this paper increase the understanding of dual-comb generation inside a single cavity laser and may contribute in future attempts to increase the stabilization of this regime.

Vector solitons with locked and precessing states of polarization.

We demonstrate experimentally new families of vector solitons with locked and precessing states of polarization for fundamental and multipulse soliton operations in a carbon nanotube mode-locked fiber laser with anomalous dispersion laser cavity.

Activated polarization pulling and de-correlation of signal and pump states of polarization in a fiber Raman amplifier.

We report on a theoretical study of activated polarization pulling and de-correlation of signal and pump states of polarization based on an advanced vector model of a fiber Raman amplifier accounting for random birefringence and two-scale fiber spinning. As a result, we have found that it is possible to provide de-correlation and simultaneously suppress PDG and PMD to 1.2 dB and 0.035 ps/km(1/2) respectively.

Synthesis of 4-aminoquinazolines by palladium-catalyzed intramolecular imidoylation of N-(2-bromoaryl)amidines.

Compared with the widespread use of carbonylative Pd-catalyzed cross-coupling reactions, similar reactions involving isocyanide insertion are almost virgin territory. We investigated the intramolecular imidoylative cross-coupling of N-(2-bromoaryl)amidines, leading to 4-aminoquinazolines. After thorough optimization of the reaction with respect to palladium source and loading, ligand, base, temperature, and solvent, a small library of 4-aminoquinazolines was prepared to determine the scope of this method. Various substituents are tolerated on the amidine and the isocyanide, providing efficient access to a broad range of diversely substituted 4-aminoquinazolines of significant pharmaceutical interest.

Synthesis of functionalized pyridazin-3(2H)-ones via selective bromine-magnesium exchange and lactam directed ortho C-H magnesiation.

Selective bromine-magnesium exchange on 2-benzyl-5-bromo-4-methoxypyridazin-3(2H)-one could be achieved when MesMgBr was used as reagent. With more nucleophilic RMgCl species (R = Bu, i-Pr, Ph) both nucleophilic addition-elimination at C-4 and bromine-magnesium exchange at C-5 occurred. In 2-benzyl-5-bromopyridazin-3(2H)-one, which does not contain a substituent at C-4, addition could not be suppressed. Less nucleophilic Mg amides (TMPMgCl·LiCl) allowed regioselective C-H magnesiation at the C-4 position in such substrates, as exemplified for 2-benzyl-5-chloro- and 2-benzyl-6-chloropyridazin-3(2H)-one. Quenching of the magnesiated pyridazinones with electrophiles gives access to a variety of hitherto unknown pyridazin-3(2H)-one derivatives.

Coherence and anticoherence resonance in high-concentration erbium-doped fiber laser.

We report an experimental study of low-frequency (~10 kHz) self-pulsing of the output intensity in a high-concentration erbium-doped fiber laser. We suggest that the fast intensity fluctuations caused by multimode and polarization instabilities play the role of an external noise source, leading to low-frequency auto-oscillations through a coherence resonance scenario.

Symmetrical and nonsymmetrical chromophores with Tröger's base skeleton: chiroptical, linear, and quadratic nonlinear optical properties--a joint theoretical and experimental study.

We report on the novel chiral push-pull chromophores derived from 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (Tröger's base skeleton). The synthesis of symmetrical chromophores featuring two identical acceptors, as well as the synthesis of unsymmetrical chromophores featuring only one acceptor is given. Symmetrical chromophores were prepared in the enantiomerically pure form and their chiroptical properties were investigated. Second-order nonlinear optical (NLO) properties of new chromophores were investigated with the aid of hyper-Rayleigh scattering (HRS). The detailed theoretical analysis of the second-order NLO properties of the chromophores was also undertaken. The joint theoretical and experimental studies of chromophores derived from Tröger's base skeleton, in comparison with benchmark chromophores featuring a dimethylamino group as the donor, provided insight into the relationship between the structure of the new chromophores and their NLO properties.

Synthesis and supramolecular organization of regioregular polythiophene block oligomers.

The self-assembly of functional polythiophenes was studied by a bottom-up approach "from molecule to polymer". The synthesis and the X-ray structure of 2,5-dibromo-3-styryl and 3-2',3',4',5',6'-pentafluorostyryl-thiophenes revealed a supramolecular arrangement controlled by pi-pi interactions between the aromatic rings. A [2 + 2] photocyclization reaction in the solid state of (E)-1-2',5'-dibromo-3'-thienyl-2-pentafluorophenylethene triggers the formation of a rare cycloadduct comprising thiophene rings. The X-ray analysis confirmed its rctt stereochemistry. The synthesis of P3HT-b-P3ST and P3HT-b-P3STF block oligomers was achieved by a GRIM method in good yields. An indirect proof of well-defined nanostructured organization was provided by the partial photocyclization of pendant styryl moieties under UV irradiation.