Absence Of Strong Acids Research Articles

Direct β-Alkenylation of Ketones via Pd-Catalyzed Redox Cascade.

A direct β-alkenylation of simple ketones with alkenyl bromides is reported via a Pd-catalyzed redox cascade strategy. The reaction is redox neutral and directing-group-free, in the absence of strong acids or bases. Both cyclic and linear ketones are suitable substrates, and various alkenyl bromides can be coupled. The resulting β-alkenyl ketones are readily derivatized through diverse alkene functionalization.

CO2 Reduction Pathways on MnBr(N-C)(CO)3 Electrocatalysts

MnBr(N-ethyl-N′-2-pyridylimidazol-2-ylidine)(CO)3 reduces CO2 to CO in the absence of strong acids. Herein, we employ density functional theory and domain based local pair natural orbital coupled cluster theory to perform the first mapping of the catalytic pathway for this catalyst and various derivatives. The benzimidazole-containing derivative proceeds along the same pathway as its parent complex, but with an increased barrier to H+ reduction. The phenolated complex shows barrierless CO2 addition to the activated catalyst and facile C–O bond cleavage. All species exhibit a novel pyridine dissociation upon one-electron reduction of the tetracarbonyl species, but the active tricarbonyl catalysts can be regenerated with a small barrier. This novel step in the pathway presents a further consideration in the design of catalysts and provides insight into the potential degradation pathways of this catalyst.

ChemInform Abstract: Mild and Efficient TBAI‐Catalyzed Synthesis of 1,2,3‐Benzotriazine‐4‐(3H)‐ones from tert‐Butyl Nitrite and 2‐Aminobenzamides under Acid‐Free Conditions.

Abstract A facile and efficient annulation of 2-aminobenzamides and tert-butyl nitrite was developed, affording 1,2,3-benzotriazine-4-(3H)-ones in good yields under mild conditions. Notably, the reaction was carried out in the absence of strong acid and tert-butyl nitrite was employed as the nitrogen source.

Mild and efficient TBAI-catalyzed synthesis of 1,2,3-benzotriazine-4-(3H)-ones from tert-butyl nitrite and 2-aminobenzamides under acid-free conditions

A facile and efficient annulation of 2-aminobenzamides and tert-butyl nitrite was developed, affording 1,2,3-benzotriazine-4-(3H)-ones in good yields under mild conditions. Notably, the reaction was carried out in the absence of strong acid and tert-butyl nitrite was employed as the nitrogen source.

Synthesis and structure of stable water-soluble phosphonium alkanoate zwitterions derived from 1,3,5-triaza-7-phosphaadamantane

1,3,5-triaza-7-phosphaadamantane (PTA) was shown to form phosphonium alkanoate zwitterions with unsaturated dicarboxylic acids in water in the absence of strong acids. Solid-state structures of the phosphonium salt (1) derived from maleic or fumaric acids and that of the zwitterionic product (2) of the reaction of PTA with citraconic and mesaconic acids were determined by single-crystal X-ray diffraction. DFT calculations gave insight into the mechanism of the reaction, including the relative reactivity of the four dicarboxylic acids, and revealed the reasons for the lack of phosphonium salt formation by PTA in strongly acidic aqueous solutions.

Propargyl radical chemistry: renaissance instigated by metal coordination.

Over the last two decades, radical chemistry of propargyl systems was developed into a potent synthetic field providing access to classes of organic compounds that are otherwise hardly accessible. The levels of diastereoselection thus achieved (up to 100%) are unprecedented for free propargyl radicals, as well as for organic radicals π-bonded to transition metals. These advances were enabled by the coordination of the triple bond to a Co2(CO)6 core that precluded an acetylene-allene rearrangement, stabilized requisite propargyl cations, created conformational constraints at the carbon-carbon bond formation site, configurationally altered the acetylenic moiety allowing for 1,3-steric induction upon the newly formed stereocenters, increased bulkiness of propargyl triads thus controlling the spatial orientation of converging radicals, and allowed for α-to-γ projection of the reaction site and alteration of the transiency of radical intermediates. In the course of these studies, a number of popular "beliefs" were proven to be untrue. First, cobalt-complexed propargyl cations, which have long been considered to be thermally labile species, were engaged in synthetically meaningful transformation at temperatures as high as 147 °C. Second, in radical dimerization reactions, higher reaction temperatures did not adversely impact the yields and levels of d,l-diastereoselectivity. Third, π-bonded organometallic radicals, deemed unruly, were effectively controlled with complementary mechanistic tools, thus achieving the highest levels of stereoselectivity (up to 100%) in inter- and intramolecular reactions. Fourth, meso stereoisomers, being thermally labile and kinetically disfavored, were discovered to be major products in intramolecular cyclizations induced by cobaltocene. Fifth, propargyl cations were synthesized in the absence of strong acids, thus increasing the functional tolerance and achieving a long sought after compatibility with acid-sensitive functionalities. A concept of sequestered propargyl radicals was introduced to explain disparity in diastereoselectivity data: heterogeneous reducing agents allegedly produce "free" radicals, while homogeneous reductants generate "sequestered" radicals associated with reductant-derived oxidized species. Among mechanistic tools, a 1,3-steric induction was found to be most efficient for controlling the stereoselectivity of radical reactions (up to 100% d,l). In intramolecular reactions, a d,l-to-meso reversal of stereoselectivity was discovered with zinc being replaced with cobaltocene as a reductant. Among efficient tools for controlling the stereoselectivity in intramolecular cyclizations is a rigidity of the carbon tether that provides for an exclusive formation of d,l-diastereomers. Two novel reactions that belong to a new field of unorthodox organometallic radical chemistry were discovered: the spontaneous conversion of cobalt-complexed propargyl cations to radicals and the THF-mediated process wherein a THF molecule assumes a new role of an initiator in radical reactions. A multistep mechanism involves a THF-induced alteration of propargyl cations that facilitates a redox process between metal clusters. Novel stereoselective methods provide access to topologically and functionally diverse 3,4-diaryl and 3,4-dialkyl-1,5-alkadiynes, 3,4-disubstituted 1,5-cycloalkadiynes (C8-C12), 3,4-dialkoxy-1,5-(cyclo)alkadiynes, and 3,7-diene-1,9-alkadiynes, which can be used in targeted syntheses of organic assemblies of relevance to medicinal chemistry, materials science, and natural product syntheses. Novel mechanistic tools and methodologies for controlling stereoselectivity in radical reactions can be expanded toward new types of π-bonded unsaturated units (dienes, arenes, diynes, and enynes) and transition metals other than cobalt (Fe, Cr, Mo, W, and Mn).

Scope of the allylation reaction with [RuCp(PP)]+ catalysts: changing the nucleophile or allylic alcohol

AbstractThe scope of the dehydrative allylation reaction using allyl alcohol as allyl donor with [RuCp(PP)]+ complexes as catalysts is explored. Aliphatic alcohols are successfully allylated with allyl alcohol or diallyl ether, obtaining high selectivity for the alkyl allyl ether. The reactivity of aliphatic alcohols is in the order of primary > secondary ≫ tertiary. The tertiary alcohol 1‐adamantanol reacts extremely slowly in the absence of strong acid, but when HOTs is added, reasonable yields of 1‐adamantyl allyl ether are obtained. The alkyl allyl ether is found to be the thermodynamically favored product over diallyl ether. Apart from alcohols, thiols and indole are also efficiently allylated, while aniline acts as a catalyst inhibitor. Allylation reactions with various substituted allylic alcohols give products with retention of the substitution pattern. It is proposed that a Ru(IV) σ‐allyl species plays a key role in the mechanism of these allylation reactions. Copyright © 2010 John Wiley & Sons, Ltd.

Catalytic Selectivity of Ketalization Versus Transesterification

Selective ketalization of levulinic acid esters (LAE’s) provides an industrial pathway for developing novel, renewable building blocks for the synthesis of novel polymers, functional oligomers, polymer additives, and solvents. Using a relatively low amount of moderate to strong protic acid catalyst resulted in selective formation of ketal at >95% and conversion >95%, without sacrificing reaction speed. The hydrostability of the ketal-ester was also studied in the presence or absence of strong acid. The ketals showed similar hydrostability compared to an ester and superior hydrostability relative to an anhydride in the absence of strong acid.

Effect of acid catalysts and accelerated aging on the reaction of methanol with hydroxy-acetaldehyde in bio-oil

Bio-oil is a promising alternative source of energy produced from fast pyrolysis of biomass. Increasing the viscosity of bio-oil during storage is a major problem that can be controlled by the addition of methanol or other alcohols. This paper reports the results of our investigation of the reactions of short chain alcohols with aldehydes and acids in bio-oil. The reaction of methanol with hydroxyacetaldehyde (HA) to form the acetal was catalyzed by the addition of 7 x 10-4 M strong acids such as sulfuric, hydrochloric, p-toluene sulfonic acid, and methanesulfonic acid. HA formed 2,2-dimethoxyethanol (DME), and at 60 oC the equilibrium was reached in less than one hour. Smaller amounts of DME were formed in the absence of strong acid. HA, acetaldehyde, and propanal formed their corresponding acetals when reacted with methanol, ethanol, 1-propanol or 1-butanol. Esters of acetic acid and hydroxyacetic acid were observed from reactions with these same four alcohols. Other acetals and esters were observed by GC/MS analysis of the reaction products. The results from accelerated aging experiments at 90 oC suggest that the presence of methanol slows polymerization by formation of acetals and esters from low molecular weight aldehydes and organic acids.

Anionic Ring-opening Polymerization of Alkyl 1-Cyanocyclopropanecarboxylates

Poly(alkyl 1-cyanotrimethylene-1-carboxylate)s (CH2CH2C(CN)(COOR))n are the next higher chain homologues of poly(α-cyanoacrylate)s. They were synthesized via the anionic ring-opening polymerization of the corresponding alkyl 1-cyanocyclopropanecarboxylate monomers initiated with thiophenolate salts (PhSM, with M = Li, Na, K, and NBu4) and at temperatures above 50 °C. Precipitation of the growing polymer chains at an early stage during the polymerization did not prevent further propagation, probably via polymerization in the solid or at the solid surface. The propagating cyanoacetate carbanion is very stable in a normal air atmosphere, surviving for long periods of time in the absence of strong acids. Although monodisperse polymers were obtained in most experiments (M̄w/M̄n < 1.10), strong experimental evidence for a living polymerization could only be obtained when K+ and NBu4+ counterions were used. Nonquantitative initiations characterized polymerizations initiated by PhSLi and PhSNa. Attempted polymerizations of ethyl 1-cyanocyclobutanecarboxylate failed under similar or slightly more energetic experimental conditions, with the thiophenolate initiator attacking the pendant ester rather than the cyclic methylene group.

New Synthetic Reactions Based on the Onium Salts of Aza‐Arenes [New synthetic methods (29)

AbstractEffective syntheses employing 2‐halogenated pyridinium, benzoxazolium, benzothiazolium, and pyridinium salts have been accomplished in the absence of strong acids and bases. Activation of carboxylic acids or alcohols with these onium salts leads to 2‐acyloxy and 2‐alkoxy intermediates which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides isocyanates, isothiocyanates, nitriles, and isocyanates. The possibility of performing stereospecific syntheses (involving configurational inversion) with onium salts deserves attention.

Kinetics of the oxidation of ethylbenzene by cobaltic acetate in acetic acid

Under nitrogen and in the absence of strong acid, the reduction of cobaltic acetate by oxidation of ethylbenzene in acetic acid obeys kinetics that can be explained by assuming that cobalt are associated in the dinuclear species CoIII–CoIII and CoIII–CoII, only the former being active for oxidation. In the presence of trichloroacetic acid, similar kinetics are observed except that no inactivation of CoIII by CoII apparently takes place. In both cases, the experimental data are consistent with a mechanism whereby ethylbenzene is attacked by the cobaltic species to yield reversibly a benzylic radical. This scheme is further confirmed by the kinetics of oxygen uptake determined when the reaction is carried out in air.

Mechanisms of Acid Catalysis. The Kinetics and Mechanisms of the Acid-catalyzed Reactions of Ethyl Diazoacetate with Ethanol and Acetic Acid1

The p-toluenesulfonic acid-catalyzed reaction of ethyl diazoacetate with ethanol has been found to have different hydrogen isotope and solvent effects from the formally similar reaction with diphenyldiazomethane. Deuterium-exchange experiments have demonstrated that ethyl diazoacetate is involved in a rapid and reversible equilibrium with the corresponding diazonium ion with p-toluenesulfonic acid in ethanol, in the absence of strong acid in acetic acid or with acetic acid in benzene. It is concluded that the general-acid and “specific-oxonium” catalyzed reactions of diazo compounds involve different types of mechanisms.