Selective Late‐Stage Sulfonyl Chloride Formation from Sulfonamides Enabled by Pyry‐BF4

Reported here is a simple and practical functionalization of primary sulfonamides, by means of a pyrylium salt (Pyry‐BF₄), with nucleophiles. This simple reagent activates the poorly nucleophilic NH₂ group in a sulfonamide, enabling the formation of one of the best electrophiles in organic synthesis: a sulfonyl chloride. Because of the variety of primary sulfonamides in pharmaceutical contexts, special attention has been focused on the direct conversion of densely functionalized primary sulfonamides by a late‐stage formation of the corresponding sulfonyl chloride. A variety of nucleophiles could be engaged in this transformation, thus permitting the synthesis of complex sulfonamides, sulfonates, sulfides, sulfonyl fluorides, and sulfonic acids. The mild reaction conditions and the high selectivity of Pyry‐BF₄ towards NH₂ groups permit the formation of sulfonyl chlorides in a late‐stage fashion, tolerating a preponderance of sensitive functionalities.     

Lattice Opening upon Bulk Reductive Covalent Functionalization of Black Phosphorus

The chemical bulk reductive covalent functionalization of thin‐layer black phosphorus (BP) using BP intercalation compounds has been developed. Through effective reductive activation, covalent functionalization of the charged BP by reaction with organic alkyl halides is achieved. Functionalization was extensively demonstrated by means of several spectroscopic techniques and DFT calculations; the products showed higher functionalization degrees than those obtained by neutral routes.     

Antifungal activity against Botrytis cinerea of labdane-type diterpenoids isolated from the resinous exudate of Haplopappus velutinus Remy (Asteraceae)

Two labdane diterpenoids were isolated, from the resinous exudate of Haplopappus velutinus Remy (Asteraceae); the main compound was identified as 7,13-(E)-labdadien-15,18-dioic-acid-18-methyl ester (1) and the minor compound identified as 7-labden-15,18-dioic-acid-18-methyl ester (2). Their structures were obtained using FTIR, MS, HRMS and NMR data: 1D NMR (¹H, ¹³C and DEPT-135), 2D homonuclear NMR (COSY and NOESY) and heteronuclear NMR (HSQC and HMBC). The trans stereochemistry of the decalin moiety of compounds 1 and 2 was established through NOESY experiments of the reduction product of 1; 7-labden-15,18-diol (1a). Diterpenoids 1 and 1a are described for the first time and showed antifungal activity, inhibiting approximately 40% mycelial growth of Botrytis cinerea.     

Stereospecific Synthesis of α‐Hydroxy‐Cyclopropylboronates from Allylic Epoxides

Herein, we report a catalytic and stereospecific method for the preparation of enantioenriched α‐hydroxy cyclopropylboronates with control in four contiguous stereocenters. The reaction involves the borylation of readily available allylic epoxides using an inexpensive Cu(I) salt and a commercially available phosphine ligand. High diastereocontrol is achieved and different diastereomers can be selectively prepared. Functionalization of the carbon–boron bond provides access to different enantiomerically enriched trisubstituted cyclopropanes from a common intermediate.     

A Stochastic Version of the Noether Theorem

A stochastic version of the Noether theorem is derived for systems under the action of external random forces. The concept of moment generating functional is employed to describe the symmetry of the stochastic forces. The theorem is applied to two kinds of random covariant forces. One of them generated in an electrodynamic way and the other is defined in the rest frame of the particle as a function of the proper time. For both of them, it is shown the conservation of the mean value of a random drift momentum. The validity of the theorem makes clear that random systems can produce causal stochastic correlations between two faraway separated systems, that had interacted in the past. In addition possible connections of the discussion with the Ives Couder’s experimental results are remarked.     

A Numerical Study of the Flow Around a Model Winged Seed in Auto-Rotation

In this study the flow around a winged-seed in auto-rotation is characterized using direct numerical simulations (DNS) at Reynolds number in the range 80–240, based on the descent speed and a characteristic chord length. In this range, the flow is approximately steady when observed from a reference frame fixed to the seed. For all cases, the flow structure consists of a wing tip vortex which describes a helical path, a vortex shed behind the nut of the seed and a stable leading edge vortex above the wing surface which merges with the tip vortex. With increasing Reynolds number, the leading edge vortex becomes more intense and gets closer to the wing surface. The simulation results also show the formation of a spanwise flow on the upper surface of the wing, moving fluid towards the wing tip in a region downstream and beneath the leading edge vortex. This spanwise flow is rather weak inside the core of the leading edge vortex, and the analysis of the streamlines show a very weak transport of vorticity along the vortex for the cases under consideration. The analysis of the flow suggests that the stabilization of the leading edge vortex is mainly due to non-inertial accelerations, although viscous effects may contribute, specially at lower Re. Furthermore, the leading edge vortex has been characterized by analysing the flow variables averaged along cross-sections of the vortex. While some quantities, like the spanwise velocity or the pressure inside the vortex, are rather insensitive to the threshold used to define the leading edge vortex, the same is not true for the circulation of the vortex or its averaged spanwise vorticity, due to the viscous nature of the vortex. Finally, it is observed that the spanwise vorticity scales with the angular rotation of the seed for the different Re.     

Base-controlled mechanical systems and geometric phases

In this paper, we carry a detailed study of mechanical systems with configuration space Q?Q/G$Q?Q/G$ for which the base Q/G$Q/G$ variables are being controlled. The overall system’s motion is considered to be induced from the base one due to the presence of general non-holonomic constraints. It is shown that the solution can be factorized into dynamical and geometrical parts. Moreover, under favorable kinematical circumstances, the dynamical part admits a further factorization since it can be reconstructed from an intermediate (body) momentum solution, yielding a reconstruction phase formula. Finally, we apply this results to the study of concrete mechanical systems.     

Propagation of non-diffracting intense ultraviolet beams

Ultraviolet pulses of 200 ps duration are focused in vacuum, and launched into the atmosphere through an aerodynamic window. Instead of diffracting, above a threshold of 100 mJ, the beam propagates in a self-induced waveguide in air. The peak electric field and beam profile are consistent with the eigenfunction of a modified nonlinear Schrödinger equation. The evolution of the beam waist with distance is calculated by a combination of the nonlinear Schrödinger equation and an equation for the nonlinear losses.     

Phase recovery in temporal speckle pattern interferometry using the generalized S-transform

We propose a novel approach based on the generalized S-transform to retrieve optical phase distributions in temporal speckle pattern interferometry. The performance of the proposed approach is compared with those given by well-known techniques based on the continuous wavelet, the Hilbert transforms, and a smoothed time-frequency distribution by analyzing interferometric data degraded by noise, nonmodulating pixels, and modulation loss. The advantages and limitations of the proposed phase retrieval approach are discussed.     

Stochastic hard-sphere dynamics for hydrodynamics of nonideal fluids

A novel stochastic fluid model is proposed with a nonideal structure factor consistent with compressibility, and adjustable transport coefficients. This stochastic hard-sphere dynamics (SHSD) algorithm is a modification of the direct simulation Monte Carlo algorithm and has several computational advantages over event-driven hard-sphere molecular dynamics. Surprisingly, SHSD results in an equation of state and a pair correlation function identical to that of a deterministic Hamiltonian system of penetrable spheres interacting with linear core pair potentials. The fluctuating hydrodynamic behavior of the SHSD fluid is verified for the Brownian motion of a nanoparticle suspended in a compressible solvent.