Production of Tartrates by Cyanide-Mediated Dimerization of Glyoxylate: A Potential Abiotic Pathway to the Citric Acid Cycle

An abiotic formation of <i>meso</i>- and dl-tartrates in 80% yield via the cyanide-catalyzed dimerization of glyoxylate under alkaline conditions is demonstrated. A detailed mechanism for this conversion is proposed, supported by NMR evidence and ¹³C-labeled reactions. Simple dehydration of tartrates to oxaloacetate and an ensuing decarboxylation to form pyruvate are known processes that provide a ready feedstock for entry into the citric acid cycle. While glyoxylate and high hydroxide concentration are atypical in the prebiotic literature, there is evidence for natural, abiotic availability of each. It is proposed that this availability, coupled with the remarkable efficiency of tartrate production from glyoxylate, merits consideration of an alternative prebiotic pathway for providing constituents of the citric acid cycle

Palladium-Catalyzed Suzuki Reactions in Water with No Added Ligand: Effects of Reaction Scale, Temperature, pH of Aqueous Phase, and Substrate Structure

The heterogeneous palladium-catalyzed Suzuki reactions between model aryl bromides (4-bromoanisole, 4-bromoaniline, 4-amino-2-bromopyridine, and 2-bromopyridine) and phenylboronic acid have been successfully conducted in water with no added ligand at the 100 mL scale using 20–40 mmol of aryl bromide. The product yields associated with these substrates were optimized, and key reaction parameters affecting the yields were identified. The results clearly indicate that the reaction parameters necessary to achieve high yields are substrate-dependent. In addition, it is demonstrated that aqueous Suzuki reactions of substrates containing basic nitrogen centers can produce quantitative yields of desired products in the absence of added ligand

Aqueous Suzuki Coupling Reactions of Basic Nitrogen-Containing Substrates in the Absence of Added Base and Ligand: Observation of High Yields under Acidic Conditions

A series of aqueous heterogeneous Suzuki coupling reactions of substrates containing basic nitrogen centers with phenylboronic acid in the absence of added base and ligand is presented. High yields of products were obtained by employing aryl bromides containing aliphatic 1°, 2°, and 3° amine substituents, and good to high yields were obtained by employing a variety of substituted bromopyridines. In the former series, the pH of the aqueous phase changed from basic to acidic during the course of the reaction, while in the latter series the aqueous phase was on the acidic side of the pH scale throughout the entire course of reaction. A mechanistic interpretation for these observations, which generally preserves the oxo palladium catalytic cycle widely accepted in the literature, is presented

Mechanism of Acid-Catalyzed Decomposition of Dicumyl Peroxide in Dodecane: Intermediacy of Cumene Hydroperoxide

Acid-catalyzed decomposition of dicumyl peroxide in dodecane from 60 to 130 °C produces α-methylstyrene and phenol as the major products. Pseudo-first-order rate constants were determined as a function of the temperature for the reaction of DCP with dodecylbenzenesulfonic acid in dodecane and resulted in an <i>Arrhenius plot exhibiting two distinct kinetic regimes</i> with differing activation energies: 76.9 kJ/mol at low temperatures (measured from 60 to 90 °C) and 8.50 kJ/mol at higher temperatures (measured from 90 to 130 °C). With employment of a combination of kinetics, product analysis, and trapping experiments, evidence is presented to show the intermediacy of <i>cumene hydroperoxidea reactive intermediate absent from previous mechanistic descriptions of this process.</i> The yield of cumene hydroperoxide production is discussed, and the mechanistic pathways for formation of the observed products are presented

COSMO-RS Studies: Structure–Property Relationships for CO₂ Capture by Reversible Ionic Liquids

The quantum-chemical approach COSMO-RS was used to develop structure–property relationships of reversible ionic-liquid (RevIL) solvents for CO₂ capture. Trends predicted for the thermodynamic properties of the RevILs using COSMO-RS, such as CO₂ solubility, solvent regeneration enthalpy, and solvent reversal temperature, were verified by experimental data. This method was applied to a range of structures, including silylamines with varying alkyl chain lengths attached to the silicon and amine functionality, silylamines with fluorinated alkyl chains, sterically hindered silylamines and carbon-based analogues. The energetics of CO₂ capture and release and the CO₂ capture capacities are compared to those of the conventional capture solvent monoethanolamine. The results of this study suggest that the simple COSMO-RS computational approaches reported herein can act as a guide for designing new RevILs. COSMO-RS allows for the determination of the relative thermodynamic properties of CO₂ in these and related systems

A Tandem, Bicatalytic Continuous Flow Cyclopropanation-Homo-Nazarov-Type Cyclization

Continuous flow processing represents an emerging technology in the chemical and pharmaceutical industries. Herein, we describe a tandem, bicatalytic continuous flow cyclopropanation-homo-Nazarov-type ring-opening cyclization to form hydropyrido­[1,2-<i>a</i>]­indoles, which represents a naturally occurring chemical scaffold present in many bioactive and therapeutically relevant molecules. The tandem flow reactions provided high conversions (>97%) with product throughputs on the order of 3–5 g h^–1. The individual transformations (cyclopropanation and ring-opening cyclization) were separately optimized in the batch then successfully transferred to the flow. Significantly, this represents the first literature example of continuous flow cyclopropane ring-opening cyclizations; hydropyrido­[1,2-<i>a</i>]­indoles are formed on a multigram scale (>4 g h^–1 throughput) in near-quantitative yields from <i>N</i>-indolyl-1,1-cyclopropyl β-amidoesters. Overall, the continuous flow technology exhibited superior yields, relative to the batch reactions, for both the ring-opening cyclizations and the tandem, bicatalytic reactions. These results provide the basis for large-scale implementation of bicatalytic cyclopropanation-ring-opening cyclization reactions for complex synthesis and represent initial efforts toward the development of an industrially viable, four-step continuous flow synthesis of hydropyrido­[1,2-<i>a</i>]­indoles