Regiocontrolled Ru-catalyzed addition of carboxylic acids to alkynes: practical protocols for the synthesis of vinyl esters

The catalytic activity of commercially available, air and water stable ruthenium complexes in the addition of carboxylic acids to terminal alkynes was found to be drastically enhanced by the addition of small quantities of base. Moreover, the regioselectivity of the reaction can be controlled by the choice of the base so that both the Markovnikov (Na2CO3) and the anti-Markovnikov products (DMAP) are now easily accessible in excellent selectivities.     

Accelerated microdroplet synthesis of benzimidazoles by nucleophilic addition to protonated carboxylic acids

We report a metal-free novel route for the accelerated synthesis of benzimidazole and its derivatives in the ambient atmosphere. The synthetic procedure involves 1,2-aromatic diamines and alkyl or aryl carboxylic acids reacting in electrostatically charged microdroplets generated using a nano-electrospray (nESI) ion source. The reactions are accelerated by orders of magnitude in comparison to the bulk. No other acid, base or catalyst is used. Online analysis of the microdroplet accelerated reaction products is performed by mass spectrometry. We provide evidence for an acid catalyzed reaction mechanism based on identification of the intermediate arylamides. Their dehydration to give benzimidazoles occurs in a subsequent thermally enhanced step. It is suggested that the extraordinary acidity at the droplet surface allows the carboxylic acid to function as a C-centered electrophile. Comparisons of this methodology with data from thin film and bulk synthesis lead to the proposal of three key steps in the reaction: (i) formation of an unusual reagent (protonated carboxylic acid) because of the extraordinary conditions at the droplet interface, (ii) accelerated bimolecular reaction because of limited solvation at the interface and (iii) thermally assisted elimination of water. Eleven examples are shown as evidence of the scope of this chemistry. The accelerated synthesis has been scaled-up to establish the substituent-dependence and to isolate products for NMR characterization.

We report a metal-free novel route for the accelerated synthesis of benzimidazole and its derivatives in the ambient atmosphere.     

Gold(I)-catalyzed intermolecular addition of phenols and carboxylic acids to olefins

Ph3PAuOTf can catalyze efficient intermolecular addition of phenols and carboxylic acids to olefins under relatively mild conditions.     

Ruthenium complex catalyzed selective addition of carboxylic acids to acetylenes giving enol esters

Carboxylic acids react with acetylenes in the presence of a catalytic amount of bis(η⁵-cyclooctadienyl)ruthenium-PR₃-maleic anhydride in toluene to give enol esters in good to excellent yields with high regioselectivity.     

Metal-free synthesis of aryl esters by coupling aryl carboxylic acids and aryl boronic acids

A facile synthesis of aryl esters is developed by coupling aryl carboxylic acids and aryl boronic acids in the presence of PhI(OAc)₂ and carbonyl diimidazole. A wide range of functional groups were tolerant to the metal-free reaction condition that led to the desired products in good yields.     

One-pot synthesis of homoallylic ketones from the addition of vinyl grignard reagent to carboxylic esters

Fifteen homoallylic ketones have been synthesized in 26-77% yields on treatment of aromatic, aliphatic, and alpha-amino methyl carboxylates with excess vinylmagnesium bromide and catalytic amounts of a copper salt in THF. Alpha-amino homoallylic ketones derived from N-protected alpha-amino esters possessing aliphatic and alcohol side chains were synthesized in > or =98% enantiomeric purity. [reaction: see text]     

Phase-transfer catalyzed synthesis of 2-propenyl esters of carboxylic acids

Summary The tetrabutylammonium bromide catalyzed esterification of salts of carboxylic acids1 a–e with 2-propenyl halides2 a,b is described.

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Phasentransferkatalysierte Synthese von 2-Propenylestern von Carbonsäuren (Kurze Mitt.)

Zusammenfassung Es wird die tetrabutylammoniumkatalysierte Veresterung von Carbonsäuresalzen1 a–e mit 2-propenylhalogeniden2 a,b beschrieben

     

Metal-free synthesis of aryl esters from carboxylic acids and diaryliodonium salts

An efficient arylation of carboxylic acids with diaryliodonium salts has been developed, giving aryl esters in high yields within short reaction times for both aromatic and aliphatic substrates. The transition-metal-free conditions are compatible with a range of functional groups, and good chemoselectivity is observed with unsymmetric diaryliodonium salts. Furthermore, steric hindrance in the ortho positions is well tolerated both in the carboxylic acid and in the diaryliodonium salt, yielding aryl esters that cannot be obtained via other esterification protocols.     

Asymmetric synthesis of protected arylglycines by rhodium-catalyzed addition of arylboronic acids to N-tert-butanesulfinyl imino esters

A new method for the Rh(I)-catalyzed addition of arylboronic acids to N-tert-butanesulfinyl imino esters has been developed for the asymmetric synthesis of arylglycine derivatives. This method provides high yields (61-90%) and diastereoselectivities (>98:2) for a variety of functionalized arylboronic acids. The N-sulfinyl arylglycine ester products are versatile intermediates for further transformations, including selective protecting group removal, conversion to beta-amino alcohols, and direct incorporation into peptides.     

Free-radical addition of aliphatic carboxylic acids to dialkyldiallylsilanes

Summary When reaction is initiated with t-butyl peroxide, carboxylic acids add to one double bond of dialkyldially lsilanes with subsequent homolytic intramolecular cyclization of the intermediately formed free radical with formation of a compound containing a silicon atom in a six-membered ring.     

Novel intermolecular carbon radical addition to a nitrone: asymmetric synthesis of alpha-amino acids

A nitrone was used as a synthetically useful radical acceptor in carbon-carbon bond-forming radical reactions; the intermolecular addition of alkyl radicals to chiral glyoxylic nitrone was studied; a high degree of stereocontrol in radical addition to glyoxylic nitrone was achieved to provide a new method for asymmetric synthesis of alpha-amino acids.     

Free radical addition of carboxylic esters to unsaturated epoxy compounds

Conclusion The addition of esters to unsaturated epoxy compounds, initiated by di-t-butyl peroxide, forms esters containing an epoxy group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, pp. 2297–2300, October, 1969.     

Advances in the synthesis of aromatic and heteroaromatic carboxylic acids and their esters

Modern approaches to the synthesis of aromatic and heteroaromatic carboxylic acids and their esters based on the latest advances in organic chemistry are compiled and systematized in this review.     

Synthesis of diesters by addition of saturated carboxylic acids to tricyclodecenyl formate

Reaction of addition of C₁-C₅-saturated monobasic acids to tricyclo[5.2.1.0^2.6]dec-3-en-8(9)-yl for-mate in the presence of a catalyst, boron trifluoride etherate (BF₃·OEt₂), was used to synthesize homo- and mixed tricyclo[5.2.1.0^2.6]decane-3(4),8(9)-diol diesters. The synthesized formic-acetic and formic-propionic acid diesters have a pleasant odor and can be used as components for preparation of perfume formulations.     

A synthesis of trisubstituted alkenes by a Ru-catalyzed addition

Catalyzed by ruthenium trisacetonitrile hexafluorophosphate 4, the Alder-ene type reaction of alkenes and internal alkynes provides an effective way to synthesize trisubstituted alkenes. Unlike most typical olefination protocols, this reaction is atom economical, and affords trisubstituted alkenes with defined olefin geometry. The regioselectivity can be explained invoking a steric argument based on the proposed mechanism. The first C-C bond formation generally involves sterically less hindered carbons of the alkenes and alkynes. Modest to very high regioselectivity can be achieved depending on the steric difference of the two substituents of alkynes.     

Rhodium-catalyzed selective anti-Markovnikov addition of carboxylic acids to alkynes

The selective intermolecular anti-Markovnikov addition of carboxylic acids to terminal alkynes yielding valuable Z-enol esters has been achieved for the first time under rhodium-catalyzed conditions. The catalyst system is applicable to a broad substrate scope and displays a wide functional group tolerance.