Enantioselective carbonyl‐directable Heck reactions using aryldiazonium salts were developed with the aim to construct chiral quaternary spiro centers in an efficient manner. Five‐ and six‐membered ...spirooxindoles, spirolactones, and spirolactams (36 examples) were obtained in good to excellent isolated yields with diastereoselectivities ranging from 13:1 to >20:1, and enantiomeric excesses up to 99% in short reaction times (1.0–1.5 h) under mild conditions (40 °C). A rationale for the diastereo‐ and enantioselectivity based on an unprecedented non‐covalent carbonyl group directing effect is also presented, and supported by computational calculations.
Unprecedented enantioselective intramolecular Heck carbonylation reactions of arenediazonium salts were enabled by a chiral N,N ligand. This reaction constitutes the first enantioselective Heck ...carbonylation that proceeds through migratory insertion followed by CO insertion. The enantioenriched functionalized dihydrobenzofurans were obtained in good to high yields and enantiomeric ratios of up to 98:2 under mild and operationally simple reaction conditions.
Enantioselective intramolecular Heck carbonylations of arenediazonium salts are enabled by a palladium catalyst in combination with a chiral N,N ligand. Enantioenriched dihydrobenzofurans were obtained through an unprecedented sequence of migratory insertion followed by CO insertion.
ABSTRACT
Predictive wavefront control is an important and rapidly developing field of adaptive optics (AO). Through the prediction of future wavefront effects, the inherent AO system servo-lag caused ...by the measurement, computation, and application of the wavefront correction can be significantly mitigated. This lag can impact the final delivered science image, including reduced strehl and contrast, and inhibits our ability to reliably use faint guide stars. We summarize here a novel method for training deep neural networks for predictive control based on an adversarial prior. Unlike previous methods in the literature, which have shown results based on previously generated data or for open-loop systems, we demonstrate our network’s performance simulated in closed loop. Our models are able to both reduce effects induced by servo-lag and push the faint end of reliable control with natural guide stars, improving K-band Strehl performance compared to classical methods by over 55 per cent for 16th magnitude guide stars on an 8-m telescope. We further show that LSTM based approaches may be better suited in high-contrast scenarios where servo-lag error is most pronounced, while traditional feed forward models are better suited for high noise scenarios. Finally, we discuss future strategies for implementing our system in real-time and on astronomical telescope systems.
We describe herein a highly regio‐ and enantioselective Pd‐catalyzed Heck arylation of unactivated trisubstituted acyclic olefins to provide all‐carbon quaternary stereogenic centers. Chiral N,N ...ligands of the pyrimidine‐ and pyrazino‐oxazoline class were developed for that purpose, providing the desired products in good to high yields with enantiomeric ratios up to >99:1. Both linear and branched substituents on the olefins were well‐tolerated. The potential of this new method is demonstrated by the straightforward synthesis of several O‐methyl lactols and lactones containing quaternary stereocenters, together with a concise enantioselective total synthesis of the calcium channel blocker verapamil.
The combination of designed chiral N,N‐based ligands and aryldiazonium salts allowed the enantioselective construction of all‐carbon quaternary stereocenters through a Heck reaction with acyclic olefins. The molecular complexity provided by this new method enabled a concise total synthesis of (R)‐verapamil.
Optical image sensors are the most common remote sensing data acquisition devices present in Unmanned Aerial Systems (UAS). In this context, assigning a location in a geographic frame of reference to ...the acquired image is a necessary task in the majority of the applications. This process is denominated direct georeferencing when ground control points are not used. Despite it applies simple mathematical fundamentals, the complete direct georeferencing process involves much information, such as camera sensor characteristics, mounting measurements, attitude and position of the UAS, among others. In addition, there are many rotations and translations between the different reference frames, among many other details, which makes the whole process a considerable complex operation. Another problem is that manufacturers and software tools may use different reference frames posing additional difficulty when implementing the direct georeferencing. As this information is spread among many sources, researchers may face difficulties on having a complete vision of the method. In fact, there is absolutely no paper in the literature that explain this process in a comprehensive way. In order to supply this implicit demand, this paper presents a comprehensive method for direct georeferencing of aerial images acquired by cameras mounted on UAS, where all required information, mathematical operations and implementation steps are explained in detail. Finally, in order to show the practical use of the method and to prove its accuracy, both simulated and real flights were performed, where objects of the acquired images were georeferenced.
Context.
Cutting-edge, ground-based astronomical instruments are fed by adaptive optics (AO) systems that are aimed at providing high performance down to the visible wavelength domain on 10 m class ...telescopes and in the near infrared for the first generation instruments of Extremely Large Telescopes (ELTs). Both applications lead to a large ratio between the telescope diameter,
D
, and the coherence length or Fried parameter,
r
0
, that is
D/r
0
. As the parameter that defines the required number of degrees of freedom of the AO system,
D/r
0
drives the requirement to reconstruct the incoming wavefront with ever-higher spatial resolution. In this context, super-resolution (SR) appears as a potential game changer. Indeed, SR promises to dramatically expand the range of spatial frequencies that can be reconstructed from a set of lower resolution measurements of the wavefront.
Aims.
As a technique that seeks to upscale the resolution of a set of measured signals, SR retrieves higher-frequency signal content by combining multiple lower resolution sampled data sets. It is well known both in the temporal and spatial domains and widely used in imaging to reduce aliasing and enhance the resolution of coarsely sampled images. This study applies the SR technique to the bidimensional wavefront reconstruction. In particular, we show how SR is intrinsically suited for tomographic multi-wavefront sensor (WFS) AO systems, revealing many of its advantages with minimal design effort.
Methods.
We provide a direct space and Fourier optics description of the wavefront sensing operation and we demonstrate how SR can be exploited through signal reconstruction, especially within the framework of periodic non-uniform sampling. We investigate both meta-uniform and non-uniform sampling schemes and we show that under some conditions, both sampling schemes enable a perfect reconstruction of band-limited signals. We also provide a SR bi-dimensional model for a Shack-Hartmann (SH) WFS, along with an analysis of the characteristics of the sensitivity function. We validated the SR concept with numerical simulations of representative multi-WFS SH AO systems. Finally, we explored the extension of the method to pyramid WFSs.
Results.
Our results show that combining several WFS samples in a SR framework grants access to a greater number of modes than the native one offered by a single WFS (despite the fixed sub-aperture size across samples). We show that the wavefront reconstruction achieved with four WFSs can be equivalent to a single WFS providing a sampling resolution that is twice greater (linear across the telescope aperture). We also show that the associated noise propagation is not degraded under SR. Finally, we show that the concept can be extended to the signal produced by single pyramid WFS, with its four re-imaged pupils serving as multiple non-redundant samples.
Conclusions.
We find that SR applied to wavefront sensing and reconstruction (WFR) offers a new parameter space to explore, as it decouples the size of the sub-aperture from the desired wavefront sampling resolution. By shifting away from outdated assumptions, new and more flexible, better-performing AO designs have now become possible.
(E)-Cinnamaldehyde is very active against Meloidogyne incognita but has low persistence in soil. To circumvent this problem, esters of cinnamic acid were evaluated as a substitute for ...(E)-cinnamaldehyde. The best results under assays with M. incognita second-stage juveniles (J2) were obtained for the methyl esters of (E)-p-fluoro- (13), (E)-p-chloro- (14), and (E)-p-bromocinnamic acid (15), which showed lethal concentrations to 50% (LC50) J2 of 168, 95, and 216 μg/mL, respectively. Under the same conditions, the LC50 values for the nematicides carbofuran and fluensulfone were 160 and 34 μg/mL, respectively. Substances 13–15 were also active against nematode eggs, which account for most of the M. incognita population in the field. According to an in silico study, substances 13–15 can act against the nematode through inhibition of histone deacetylase. Therefore, esters 13–15 and histone deacetylase are potentially useful for the rational design of new nematicides for the control of M. incognita.
Enantioselective substrate directed Heck reactions are desirable for the stereoselective synthesis of complex molecules. However, due to the coordination requirements of both chiral ligands and ...directing groups, such methodologies are underdeveloped. We report herein the desymmetrization of meso (1R,2S)‐cyclohex‐4‐ene‐1,2‐diol in an enantioselective and substrate directed fashion. The method provides all cis substituted highly functionalized chiral allylic alcohols in a complementary fashion to other Heck protocols.The products were obtained in high enantioselectivities (higher than 95% ee) and moderate to high yields (38–87%). The noncovalent interactions responsible for the directing effect were elucidated through computational examination of relevant minima and transition structures.
This review highlights the potential and the versatility of arenediazonium salts as viable alternatives to conventional aryl halides and oxygen‐based electrophiles for Pd‐catalyzed Heck reactions. It ...also presents an overview of the field over the last decade, including some historical perspective of the Heck–Matsuda (HM) reaction with general considerations regarding reaction conditions, type of catalysts used, and the application of arenediazonium salts as reagents for the HM arylation of several types of alkenes. Throughout this review, the principal aspects related to reactivity and selectivity are discussed, and when applicable a comparison is made between the HM and the conventional Heck reactions. One‐pot procedures that involve generation of the arenediazonium salt in situ from the corresponding aniline have been presented as well as some useful heterogeneous catalytic protocols. Allylic alcohols, conjugated alkenes, unsaturated heterocycles, and unactivated alkenes are capable of being arylated with arenediazonium salts by using simple catalysts such as Pd(OAc)2 or Pd2(dba)3 at room temperature in air and in benign and conventional solvents. In addition to the intramolecular variant of the HM reaction, intermolecular tandem coupling–cyclization processes have also been developed for the construction of a range of oxygen and nitrogen heterocycles. Finally, several applications towards the total synthesis of biologically active natural and nonnatural compounds are highlighted as well as the use of the HM reaction in the synthesis of new chiral, nonracemic ligands.
This review highlights the synthetic potential and the versatility of arenediazonium salts as viable electrophiles for Pd‐catalyzed Heck reactions. The principal aspects related to reactivity and selectivity are discussed, and when applicable a comparison is made between the Heck–Matsuda and the conventional Heck reactions.
Increasing consciousness regarding the nutritional value of olive oil has enhanced the demand for this product and, consequently, the expansion of olive tree cultivation. Although it is considered a ...highly resilient and tolerant crop to several abiotic stresses, olive growing areas are usually affected by adverse environmental factors, namely, water scarcity, heat and high irradiance, and are especially vulnerable to climate change. In this context, it is imperative to improve agronomic strategies to offset the loss of productivity and possible changes in fruit and oil quality. To develop more efficient and precise measures, it is important to look for new insights concerning response mechanisms to drought stress. In this review, we provided an overview of the global status of olive tree ecology and relevance, as well the influence of environmental abiotic stresses in olive cultivation. Finally, we explored and analysed the deleterious effects caused by drought (e.g., water status and photosynthetic performance impairment, oxidative stress and imbalance in plant nutrition), the most critical stressor to agricultural crops in the Mediterranean region, and the main olive tree responses to withstand this stressor.
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