Atom-economic Reaction Research Articles

Cover Picture: From Allylic Alcohols to Aldols through a New Nickel‐Mediated Tandem Reaction: Synthetic and Mechanistic Studies (Chem. Eur. J. 12/2006)

Atom economical reactions that involve mild and neutral reaction conditions are currently an important challenge in synthesis. In their Full Paper on page 3261 ff., R. Grée et al. describe a new tandem isomerization–aldolization process. The cover highlights 1) the novelty of using allylic alcohols as partners for the preparation of aldols, 2) the key role of free enols as intermediates, and 3) (in the middle) the postulated transition state of this reaction. The picture behind the scheme shows the high tide at St. Malo, a famous port and city near Rennes where this research has been performed.

A direct, efficient synthesis of unsymmetrically substituted bis(arylidene)alkanones

A direct method to unsymmetrically substituted bis(arylidene)alkanones by sequential, selective condensation reactions is reported. Analytically pure compounds were obtained in high yield using atom-economical reactions and without the need for purification of the final products. Although a two-step process could be conducted in one pot by three different methods, recrystallisation was required.

Th-W53:6 The effect of N-3 fatty acids on heart rate variability in patients treated with chronic hemodialysis

Classical cycloaddition reactions are highly atom-economical reactions toward cyclic systems, often proceeding with impressive efficiency and selectivity. Still, the development of higher-order cycloadditions (HOCs), which involve rehybridization of >6π-electrons, have presented more pronounced challenges due to the necessity of employing extended, more reactive cycloaddends. Catalytic generation of such π-systems allows for their controlled, enantioselective usage, and organocatalysis has in recent years proven a potent tool in this regard. Here, hitherto successful organocatalytic HOCs are classified based on the generated cycloaddends, and the factors that play a crucial role to the feasibility of their formation and usage are analyzed. For these reactions, aminocatalysis remains the most applied activation strategy, and the lessons obtained therefrom may provide a foundation for the elaboration of other organocatalytic strategies, of which sporadic examples demonstrate the potential for the continued growth of catalytic HOCs as a field.

Alkoxy- and hydroxycyclization of enynes catalyzed by Pd(II) and Pt(II) catalysts

Abstract The development of a novel reaction ideal in terms of atom economy was achieved. The scope of the reaction was evaluated in the presence of Pd and Pt catalysts. The first enantioselective Pt-promoted enyne carboalkoxycyclization was developed in up to 85 % stereoselectivity. This ideal atom-economical reaction afforded the corresponding functionalized five-membered carbo- and heterocycles in good to excellent yields. The use of silver salts combined with (R)-Ph-BINEPINE, a monophosphane atropisomeric ligand, was found to be the best-suited combination for moderate to high enantioselectivities on carbonated and nitrogenated substrates.

Investigation of Physicochemical Properties of Lactam-Based Brønsted Acidic Ionic Liquids

Novel lactam-cation-based Brønsted acid ionic liquids (ILs) were prepared through a simple and atom-economic neutralization reaction between a lactam, such as caprolactam and butyrolactam, and a Brønsted acid, HX, where X is BF4-, CF3COO-, phCOO-, ClCH2COO-, NO3-, or H2PO4-. The density, viscosity, acidic scale, electrochemical window, temperature dependency of ionic conductivity, and thermal property of these ILs were measured and investigated in detail. The results show that protonated caprolactam tetrafluoroborate (CPBF) has a relatively strong acidity with -0.22 of Hammett acidic scale H0 and caprolactam trifluoroacetate (CPTFA) and pyrrolidonium trifluoroacetate (PYTFA) ILs possess very low viscosities, that is, 28 cP and 11 cP, respectively. An investigation of thermal property showed that a wide liquid range (up to -90 degrees C), moderate thermal stability (up to 249 degrees C for 10% of decomposition), and complex polymorphism were observed in these ILs. In comparison to imidazolium-cation-based ILs, the lactam-cation-based Brønsted acid ILs have a relatively lower cost, lower toxicity, and comparable ion conductivity and heat storage density (more than 200 MJ/m3). They have wide applicable perspectives for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media and catalysts as replacements of conventional inorganic acids.

Microwave-Assisted Suzuki Coupling on a KF-Alumina Surface: Synthesis of Polyaryls.

Abstract A range of conjugated polyaryls has been synthesized through one-pot microwave assisted palladium-catalyzed consecutive Suzuki coupling reactions on a KF–alumina surface with notable features including rapid reaction times, solvent-free conditions, high yields, atom economic and air-insensitive reactions.

Efficient Barbier reaction of carbonyl compounds improved by a phase transfer catalyst in waterElectronic supplementary information (ESI) available: experimental procedure for allylation and spectral data for the allylation products. See http://www.rsc.org./suppdata/gc/b2/b206452a/

A phase transfer catalyst (PTC) is employed in allylation mediated by tin. This atom economical reaction was performed in water at room temperature without any assistance. In addition, the influence of PTC on diastereoselectivity of the allylation was studied.

Atom-economical synthesis of the N(10)-C(17) fragment of cyclotheonamides via a novel Passerini reaction-deprotection-acyl migration strategy.

[reaction: see text]. A novel variant of the atom-economical Passerini reaction between suitably protected argininal, dipeptide isonitrile, and proline components afforded adduct 13. Orthogonal N-deprotection of 13 led, via a smooth O- to N-acyl migration, to 14, which constitutes the N(10)-C(17) fragment of the cyclotheonamide family of serine protease inhibitors. Each reaction in this three-step protocol proceeds in good yield and under very mild conditions.

When Is a Proton Not a Proton?

In spite of the large number of protonated complexes, their use in catalytic cycles has been little explored. The existing examples suggest that catalytic processes initiated by the protonation of a low-valent metal hold promise for the development of selective, efficient, and atom-economical addition reactions under very mild conditions, if the protonation occurs with weak acids. The acidity required depends upon the basicity of the metal, and the latter can be increased by the use of more electron-rich ligands (see figure).

N-hydroxypyridine-2(1 H)-thione derivatives of carboxylic acids as activated esters. Part II. Applications in peptide synthesis

The N-hydroxypyridine-2(1 H)-thione derivatives of two urethane-protected α-amino acids readily reacted with free α-amino acid esters or the corresponding benzenesulfenamides to give simple dipeptides in reasonable yields. The benzenesulfenamides are the reagents of choice since they allowed for neutral reaction conditions and exhibited superior reactivity in sterically demanding instances. The atom-economical reaction between a Barton PTOC ester and a benzenesulfenamide afforded products of synthetic and biological value and proceeds in a concerted fashion, thereby maintaining chirality in couplings involving optically active α-amino acid residues.

Atom economical reactions help chemists eliminate waste

Atom economical reactions help chemists eliminate waste