An effective method for the synthesis of carboxylic esters and lactones using substituted benzoic anhydrides with Lewis acid catalysts

An efficient mixed-anhydride method for the synthesis of carboxylic esters and lactones using benzoic anhydride having electron withdrawing substituent(s) is developed by the promotion of Lewis acid catalysts. In the presence of a catalytic amount of TiCl₂(ClO₄)₂, various carboxylic esters are prepared in high yields through the formation of the corresponding mixed-anhydrides from 3,5-bis(trifluoromethyl)benzoic anhydride and carboxylic acids. The combined catalyst consisting of TiCl₂(ClO₄)₂ together with chlorotrimethylsilane functions as an effective catalyst for the synthesis of carboxylic esters from free carboxylic acids and alcohols with 4-(trifluoromethyl)benzoic anhydride. Various macrolactones are prepared from the free ω-hydroxycarboxylic acids by the combined use of 4-(trifluoromethyl)benzoic anhydride and titanium(IV) catalysts together with chlorotrimethylsilane under mild reaction conditions. The lactonization of trimethylsilyl ω-(trimethylsiloxy)carboxylates using 4-(trifluoromethyl)benzoic anhydride is also promoted at room temperature in the presence of a catalytic amount of TiCl₂(ClO₄)₂. An 8-membered ring lactone, a synthetic intermediate of cephalosporolide D, is successfully synthesized according to this mixed-anhydride method using 4-(trifluoromethyl)benzoic anhydride by the promotion of a catalytic amount of Hf(OTf)₄.     

An effective method for the synthesis of monoferrocenylbenzene derivatives

Three new ferrocenylbenzene derivatives, 1-ferrocenyl-2,3,4,5-tetramethylbenzene (1), 1-ferrocenyl-2,4-diphenylbenzene (2), and 1-ferrocenyl-2,4-ditrimethylsilylbenzene (3), were synthesized by cycloaddition of ferrocenylacetylene cobalt cluster with different alkynes and characterized by elemental analysis, FT-IR, NMR, and MS. The molecular structures of 2 and 3 were identified by single-crystal X-ray diffraction. The oxidation potentials of ferrocenyl unit in these compounds were investigated by cyclic voltammetry and theoretical calculations. The results indicated that the electron-donating or electron-withdrawing effect of substituents on the central phenyl was the key factor that influenced the oxidation potential of the ferrocenyl unit.     

Direct use of esters in the Mukaiyama aldol reaction: a powerful and convenient alternative to aldehydes

An indium triiodide catalyst promoted the direct transformation from esters to β-hydroxycarbonyl compounds using hydrosilanes and silyl enolates by a one-stage process. Various esters were applicable, and the high chemoselectivity of this system brings compatibility to many functional groups: alkenyl, alkynyl, chloro, and hydroxy.     

Preparation and physical properties of chitosan benzoic acid derivatives using a phosphoryl mixed anhydride system

Direct benzoylation of the two hydroxyl groups on chitosan was achieved using a phosphoryl mixed anhydride system, derived from trifluoroacetic anhydride (TFAA), benzoic acids (BAs), and phosphoric acid (PA). The reaction is operated as a one pot process under mild conditions that does not require neither an inert atmosphere nor dry solvents. The structures of the synthesized compounds were confirmed by NMR and IR spectroscopy. Solubility tests on the products revealed that they were soluble in organic solvents such as N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), and acetone. In the meantime, a morphological study by scanning electron microscopy (SEM) evidently indicated that the chitosan benzoates underwent significant structural changes after the benzoylation.     

A new method for the synthesis of 2-pyridinethiol carboxylic esters

An effective and convenient synthesis of 2-pyridinethiol esters of carboxylic esters has been developed which involves the interaction of a carboxylate salt with the S-chloroformyl derivative of 2-pyridinethiol.     

Synthesis of (9E)-isoambrettolide, a macrocyclic musk compound, using the effective lactonization promoted by symmetric benzoic anhydrides with basic catalysts

Two alternative methods for the synthesis of (9E)-isoambrettolide are established via the rapid lactonization of the free threo-aleuritic acid or its protected seco-acid using substituted benzoic anhydrides with basic catalysts. The most efficient lactonization of the threo-aleuritic acid is performed using 2-methyl-6-nitrobenzoic anhydride (MNBA) with a catalytic amount of 4-dimethylaminopyridine N-oxide (DMAPO).     

The effective use of substituted benzoic anhydrides for the synthesis of carboxamides

Various carboxamides are synthesized from the corresponding carboxylic acids and amines with high product-selectivities using 2-methyl-6-nitrobenzoic or 2,4,6-trichlorobenzoic anhydride in the presence of 4-(dimethylamino)pyridine.     

Carbonylation of diols and their ethers and esters with ruthenium catalysts: synthesis of lactones and hydroxyacids ethers and esters

Diols and their formic or acetic esters can be carbonylated to give lactones or the corresponding hydroxyacid esters of ethers in the presence of carbonylruthenium iodide systems, [Ru(CO)₃I₃]⁻/alkyl or metal iodide, at a temperature of 200°C and CO pressure of 10-20 MPa. The reaction in the case of 1,3-propanediol gives γ-butyrolactone, with a selectivity of 60-% . Side reactions of homologation to 1,4-butanediol derivatives and hydrogenolysis to n-propyl derivatives by H₂ produced by the water gas shift reaction (WGSR) also occur, together with acid-catalyzed dehydration to give linear polypropylene glycols, α,ω-diols with more than 3 carbon atoms in the chain preferentially give hydroxyacid esters and ethers.The cyclic ether by-products and linear polyether by-products can be further activated and carbonylated under the reaction conditions to give lactones or hydroxy-acid derivatives thus increasing the total yield of carbonylation products. The formation of H₂ by WGSR involving water produced by the acid-catalyzed dehydration reactions, and the subsequent hydrogenolysis and homologation reactions cannot be avoided.     

An effective method for the synthesis of unsymmetrical difurylmethane derivatives and 1,1-difuryl olefins

Unsymmetrical difurylmethane derivatives 9 and the unknown difuryl alkenes 10 were selectively obtained from carbinols 1a and 1b in two steps and with excellent yields.     

The free radical chemistry of carboxylic esters of 2-selenopyridine-N-oxide: a convenient synthesis of (L)-vinylglycine

Optically pure (L)-vinylglycine has been synthesised by two different methods. The first of these involves protected (L)-glutamate esters of $\text{N}$-hydroxy-2-seleno-pyridine. Such esters are shown to undergo the same decarboxylotive rearrangement as their thio-analogues. Oxidative elimination of the selenopyridine residue with ozone, and with the aid of hex-1-ene as sacrificial olefin for the work-up, gave the desired (L)-vinylglycine derivatives. Similarly, the modified Hunsdiecker reaction on the terminal carboxyl of suitably protected (L)-glutamic derivatives gave the nor-bromide which readily afforded the corresponding phenylselenides on treatment with phenylselenide anion. The sequence was then as above. Using the methyl ester with corbobenzyloxy protection for the amino-function an overall yield of crystalline optically pure (L)-vinylglycine of about 45% was obtained by either route.     

Boron trifluoride-catalyzed oxidation of glycal esters: An effective and mild method for their conversion into α,β-unsaturated lactones

An effective, one-step procedure for conversion of glycal and 2-acyloxyglycal esters to 2,3-unsaturated lactones has been developed, involving BF₃-induced removal of the allylic acyloxy function and oxidation with m-chloroperbenzoic acid or pyridinium chlorochromate.     

A convenient method to access long-chain and functionalised mixed methylphosphonate esters and their application in the synthesis of ionic liquids

A new method to synthesise long-chain and functionalised methylphosphonate esters and the corresponding ionic liquids is reported. The synthesis comprises the formation of dialkyl methylphosphonate esters in a S(N)2 reaction followed by the use of these esters as alkylating agents to form the corresponding, new alkyl methylphosphonate ILs.     

An improved method for the protection of carboxylic acids as 1,1-dimethylallyl esters

1,1-Dimethylallyl (DMA) esters of various N-protected amino acids have been synthesized using prenyldimethylsulfonium tetrafluroborate, a reagent that can be readily made and stored, in conjunction with catalytic CuBr. These reactions were complete within several hours and afforded DMA esters in high yields. As has been previously shown in our group, DMA esters represent a palladium-labile proctecting group for carboxylic acids that resists nucleophilic attack as a tert-butyl ester would.     

A convenient method for the synthesis of 6-enaminopurine derivatives by catalytic hydrogenation of 6-cyanomethylenepurines

6-Cyanomethylenepurines have been catalytically hydrogenated to the corresponding α-(aminomethylene)purine-6-acetic acid derivatives in good yields using dimethylformamide-benzene as solvent over Pd-C under medium pressure.     

A selective and convenient ruthenium mediated method for the synthesis of mixed acetals and orthoesters

Addition of alcohols and phenols to O-allyl compounds (allyl ethers and acrolein acetals), catalyzed by [RuCl₂(PPh₃)₃], was examined. Intramolecular addition of an OH group, leading to the formation of cyclic acetals and orthoesters, was also investigated. As a result, a new, selective and convenient method for the synthesis of symmetrical and unsymmetrical (mixed) acetals and orthoesters was developed.     

A mixed anhydride approach to the preparation of sulfinate esters and allylic sulfones: Trimethylacetic p-toluenesulfinic anhydride

A reagent combination of toluenesulfinic acid and trimethylacetyl chloride affords a putative trimethylacetic p-toluenesulfinic anhydride. This reagent has been used to prepare a series of sulfinate esters from primary and secondary alcohols. In addition, the reagent was used to convert Baylis-Hillman substrates into allylic sulfones. Attempts to use the reagent to convert amines to sulfinamides were unsuccessful. In contrast, the use of 2-pyrrolidinone afforded N-p-toluenesulfinyl pyrrolidinone in 64% yield. The use of a chiral 4-benzyl-1,3-oxazolidinone or 4-benzyl-1,3-oxazolidine-2-thione led to the isolation of S-p-tolyl p-toluenethiosulfonate.