Antimony Redox Catalysis: Hydroboration of Disulfides through Unique Sb(I)/Sb(III) Redox Cycling

The stibinidene ArSbI (Ar = [2,6-(tBuN═CH)2-C6H3], 1) reacts with S2Tol2 (Tol = p-tolyl) to form ArSbIII(STol)2 (2), which upon treatment with pinacolborane, regenerates 1. These processes unveil an unprecedented antimony redox catalysis involving Sb(I)/Sb(III) cycling for the hydroboration of organic disulfides. Elementary reaction studies and density functional theory calculations support that the catalysis mimics transition metal processes, proceeding through oxidative addition, ligand metathesis, and reductive elimination. The thiophenols and sulfidoborates generated from the hydroboration of disulfides react in situ with α,β-unsaturated carbonyl compounds with the assistance of 1 as a base catalyst. These tandem reactions establish a one-pot synthetic method for β-sulfido carbonyl compounds, in which a stibinidene functions as a redox catalyst and a base catalyst successively, illustrating the versatility and efficiency of antimony catalysis in organic synthesis.

Bismuth Redox Catalysis: An Emerging Main-Group Platform for Organic Synthesis

Bismuth has recently been shown to be able to maneuver between different oxidation states, enabling access to unique redox cycles that can be harnessed in the context of organic synthesis. Indeed, various catalytic Bi redox platforms have been discovered and revealed emerging opportunities in the field of main group redox catalysis. The goal of this perspective is to provide an overview of the synthetic methodologies that have been developed to date, which capitalize on the Bi redox cycling. Recent catalytic methods via low-valent Bi(II)/Bi(III), Bi(I)/Bi(III), and high-valent Bi(III)/Bi(V) redox couples are covered as well as their underlying mechanisms and key intermediates. In addition, we illustrate different design strategies stabilizing low-valent and high-valent bismuth species, and highlight the characteristic reactivity of bismuth complexes, compared to the lighter p-block and d-block elements. Although it is not redox catalysis in nature, we also discuss a recent example of non-Lewis acid, redox-neutral Bi(III) catalysis proceeding through catalytic organometallic steps. We close by discussing opportunities and future directions in this emerging field of catalysis. We hope that this Perspective will provide synthetic chemists with guiding principles for the future development of catalytic transformations employing bismuth.

Rational design of arsine catalysts for arsa-Wittig reaction

An acyclic arsine catalyst has been developed for the room-temperature catalytic arsa-Wittig reaction. The reaction mechanism has been computationally analyzed.

Larvicidal activity and in silico studies of cinnamic acid derivatives against Aedes aegypti (Diptera: Culicidae)

Cinnamic acid derivatives (CAD's) represent a great alternative in the search for insecticides against Aedes aegypti mosquitoes since they have antimicrobial and insecticide properties. Ae. aegypti is responsible for transmitting Dengue, Chikungunya, and Zika viruses, among other arboviruses associated with morbimortality, especially in developing countries. In view of this, in vitro analyses of n-substituted cinnamic acids and esters were performed upon 4th instar larvae (L4) of Ae. aegypti, as well as, molecular docking studies to propose a potential biological target towards this mosquitoes species. The larvicide assays proved that n-substituted ethyl cinnamates showed a more pronounced activity than their corresponding acids, in which p-chlorocinnamate (3j) presented a LC₅₀ value of 8.3 µg/mL. Thusly, external morphologic alterations (rigid and elongated body, curved bowel, and translucent or darkened anal papillae) of mosquitoes' group exposed to compound 3j, were observed by microscopy. In addition, an analytical method was developed for the quantification of the most promising analog by using high-performance liquid chromatography with UV detection (HPLC-UV). Molecular docking studies suggested that the larvicide action is associated with inhibition of acetylcholinesterase (AChE) enzyme. Therefore, expanding the larvicidal study with the cinnamic acid derivatives against the vector Ae. aegypti is important for finding search for more effective larvicides and with lower toxicity, since they have already shown good larvicidal properties against Ae. aegypti.

Catalyst- and Substituent-Controlled Regio- and Stereoselective Synthesis of Indolyl Acrylates by Lewis-Acid-Catalyzed Direct Functionalization of 3-Formylindoles with Diazo Esters

A facile and efficient In(OTf)₃- and BF₃·OEt₂-catalyzed direct transformation of 3-formylindoles with diazo esters has been developed for synthesizing diverse and functionalized indolyl acrylates. This one-pot protocol furnishes various (Z)-α-hydroxy-β-indolyl acrylates, (E)-β-(2-alkoxy-2-oxoethoxy)-α-indolyl acrylates, and (Z)-3-hydroxy-2-indolyl acrylates by a catalyst- and substituent-controlled, regio- and stereoselective cascade reaction. The protocol has several advantages, including low loading of the catalyst, mild reaction conditions, broad scope, and high functional group tolerance. The synthesized compounds can be further converted into diversely functionalized materials.

Main Group Redox Catalysis of Organopnictogens: Vertical Periodic Trends and Emerging Opportunities in Group 15

A growing number of organopnictogen redox catalytic methods have emerged-especially within the past 10 years-that leverage the plentiful reversible two-electron redox chemistry within Group 15. The goal of this Perspective is to provide readers the context to understand the dramatic developments in organopnictogen catalysis over the past decade with an eye toward future development. An exposition of the fundamental differences in the atomic structure and bonding of the pnictogens, and thus the molecular electronic structure of organopnictogen compounds, is presented to establish the backdrop against which organopnictogen redox reactivity-and ultimately catalysis-is framed. A deep appreciation of these underlying periodic principles informs an understanding of the differing modes of organopnictogen redox catalysis and evokes the key challenges to the field moving forward. We close by addressing forward-looking directions likely to animate this area in the years to come. What new catalytic manifolds can be developed through creative catalyst and reaction design that take advantage of the intrinsic redox reactivity of the pnictogens to drive new discoveries in catalysis?

Systematic Study on the Catalytic Arsa-Wittig Reaction

Efficient catalytic arsa-Wittig reactions have been developed by using 1-phenylarsolane as a catalyst. A wide array of aldehydes was converted to the corresponding olefins in high yields with moderate to excellent E stereoselectivity in the presence of a catalytic amount of 1-phenylarsolane. Moreover, density functional theory calculations were carried out to afford insight into the E/Z selectivity.

C-As Bond Formation Reactions for the Preparation of Organoarsenic(III) Compounds

Potential widespread applications of organoarsenic chemistry have been limited by the inherent lack of safe and effective As-C bond formation reactions. Several alternative reagents and methods have been developed in the last few decades to address the hazards and drawbacks associated with traditional arsenic synthetic strategies. Herein, this minireview summarizes the advances made in nucleophilic, electrophilic, radical and metal-mediated As(III)-C bond formations while specifically highlighting the behavior of arsenic synthons with various well-established reagents (eg. Grignard reagents, organolithium compounds, organometallic reagents, radical initiators and Lewis/Brønsted bases). Avenues for asymmetric synthesis are also discussed, as are recent advances in organoarsenic chemistry suggesting that arsines exhibit novel reactivities independent from that of other relatively more well explored Group V cogeners.

Catalytic Wittig and aza-Wittig reactions

This review surveys the literature regarding the development of catalytic versions of the Wittig and aza-Wittig reactions. The first section summarizes how arsenic and tellurium-based catalytic Wittig-type reaction systems were developed first due to the relatively easy reduction of the oxides involved. This is followed by a presentation of the current state of the art regarding phosphine-catalyzed Wittig reactions. The second section covers the field of related catalytic aza-Wittig reactions that are catalyzed by both phosphine oxides and phosphines.

Iron-catalyzed transformations of diazo compounds

Although iron-promoted diazo transformations were only discovered during the 1990s, iron can undergo facile changes in its oxidation state and possesses distinct Lewis acid character, and these properties have afforded iron a privileged position as a catalyst in the transformations of diazo compounds. In this review, we have provided an overview of the iron-catalyzed diazo transformation reactions reported in the literature by the end of 2013 with the aim of stimulating further interest in this area of research.

"Nok": a phytosterol-based amphiphile enabling transition-metal-catalyzed couplings in water at room temperature

The third-generation designer amphiphile/surfactant, "Nok" (i.e., SPGS-550-M; β-sitosterol methoxypolyethyleneglycol succinate), soon to be commercially available from Aldrich, can be prepared in two steps using an abundant plant feedstock and β-sitosterol, together with succinic anhydride and PEG-550-M. Upon dissolution in water, it forms nanomicelles that serve as nanoreactors, which can be characterized by both cryo-TEM and dynamic light scattering analyses. Several transition-metal-catalyzed reactions have been run under micellar conditions to evaluate this surfactant relative to results obtained in nanoparticles composed of TPGS-750-M (i.e., a second-generation surfactant). It is shown that Nok usually affords yields that are, in general, as good or better than those typically obtained with TPGS-750-M, and yet is far less costly.

Organophosphorus catalysis to bypass phosphine oxide waste

The conversion of oxygen-containing compounds is often achieved by the use of phosphorus reagents. The newly formed phosphine oxide bond delivers the enthalpic gain that drives reactions, such as the Wittig, Mitsunobu, and Appel reaction, to completion. However, phosphine oxides are recognized as undesirable waste products and in the past decade several methods have emerged that address this issue by in situ regeneration of the phosphorus reagent. This Minireview outlines the two distinct strategies and underpinning research that led to these advances. The potential of the emerging field of phosphorus catalysis in chemistry is shown and new developments that may stimulate further research are described.