Intramolecular lactone annulation of activated acids with Mn(III)

Intramolecular lactone annulation of activated carboxylic acids onto olefins by manganese(III) acetate yields bicyclo[3.3.0] and [4.3.O]lactones.     

Ruthenium-catalyzed alkylative lactonization and carbocyclization

[reaction: see text] The cationic ruthenium complex [CpRu(NCCH3)3]PF6 promotes the coupling of monosubstituted allene carboxylic acids and simple alpha,beta-unsaturated olefins to form five- and six-membered lactones. The mild reaction conditions allow for the presence of various functional groups.     

Efficient enantioselective synthesis of (+)-sclareolide and (+)-tetrahydroactinidiolide: chiral LBA-induced biomimetic cyclization

An efficient enantioselective synthesis of the lactones (+)-sclareolide and (+)-tetrahydroactinidiolide has been achieved through Lewis acid-assisted chiral Brønsted acid-induced enantioselective cyclization of terpenic carboxylic acids. The reaction sequence involved the [2,3] sigmatropic rearrangement of an allylic alcohol and biomimetic cyclization of terpenic acid in the presence of (R)-2-benzyloxy-2′-hydroxy-1,1′-binaphthyl and tin tetrachloride as key steps. The cyclization gave lactones in good yield and with high enantiomeric excess.     

13C NMR Chemical shifts in bicyclo[2.2.2]octanes—iii: Hydroxy acids and lactones

A number of hydroxybicyclo[2.2.2]octane carboxylic acids and the corresponding delta lactones have been prepared, and the ¹³C NMR spectra show trends that, together with some deuteration experiments, provide a self consistent and unambiguous assignment of the resonance peaks. The effects produced by the substituents and the changes in chemical shifts brought about by the lactonization process are analysed.     

Preparation of large ring acetylenic lactones by iodo lactonisation

Reaction of ω-ene-7-yne carboxylic acids with (biscollidine)iodine(I) hexafluorophosphate led to large ring acetylenic lactones. In the case of 5- or 6-yne carboxylic acids, iodo enol lactones were preferentially obtained.     

Ammonium Iodide–Promoted Cyclization of Aryl-Substituted Carboxylic Acids

An efficient procedure was developed for direct preparation of aryl-substituted lactones from corresponding aryl carboxylic acids, which was promoted by ammonium iodide. In this protocol, aryl carboxylic acids were treated with ammonium iodide, potassium bromide, and oxidant Oxone in a mixture of acetonitrile and 2,2,2-trifluoroethanol (6:4) at room temperature for 12 h, resulting in corresponding aryl lactones in moderate to good yields.     

亚甲基[6,6]-富勒(fullerene)[60]单羧酸的合成研究

亚甲基[6,6]-fullerene[60]单羧酸是一个具有化学反应活性的fullerene[60]衍生物,可以作它合成得到一些新的具有潜在生化应用价值的水溶性fullerene[60]衍生物。本文详细报道了常规量合成亚甲基[6,6]-fullerene[60]单羧酸的技术。     

[18O]-Studien zur Carboxylbeteiligung bei der sauren Hydrolyse von γ-substituierten Carbonsäuren. 1. Mitteilung: Zum Sauerstoffaustausch von γ-Lactonen in saurer Lösung

Specifically [¹⁸O]-labelled γ-valerolactone and 4-methyl-γ-valerolactone were submitted to tracer equilibration in dilute mineral acid at reflux temperature. Though under these conditions the two lactones are known to be hydrolyzed to the extent of about 25% to the corresponding γ-hydroxy acids only the «tertiary» 4-methyl derivative lost its alkoxyl label whereas the unsubstituted «secondary» one retained it. – This may be understood on the base of two alternative mecanisms possible for lactone reformation. The results permit a quantitative evaluation of the amount of carboxyl-participation during acid hydrolysis of 4-substituted carboxylic acids to 4-monoalkylated γ-butyrolactones.     

Selective homogeneous hydrogenation of biogenic carboxylic acids with [Ru(TriPhos)H]+: a mechanistic study

Selective hydrogenation of biogenic carboxylic acids is an important transformation for biorefinery concepts based on platform chemicals. We herein report a mechanistic study on the homogeneously ruthenium/phosphine catalyzed transformations of levulinic acid (LA) and itaconic acid (IA) to the corresponding lactones, diols, and cyclic ethers. A density functional theory (DFT) study was performed and corroborated with experimental data from catalytic processes and NMR investigations. For [Ru(TriPhos)H](+) as the catalytically active unit, a common mechanistic pathway for the reduction of the C═O functionality in aldehydes, ketones, lactones, and even free carboxylic acids could be identified. Hydride transfer from the Ru-H group to the carbonyl or carboxyl carbon is followed by protonation of the resulting Ru-O unit via σ-bond metathesis from a coordinated dihydrogen molecule. The energetic spans for the reduction of the different functional groups increase in the order aldehyde < ketone < lactone ≈ carboxylic acid. This reactivity pattern as well as the absolute values are in full agreement with experimentally observed activities and selectivities, forming a rational basis for further catalyst development.     

Novel functionalizations of [60]fullerene-fused lactones

Reactions of [60]fullerene-fused lactones with methylmagnesium bromide and diisobutylaluminum hydride afforded rare fullerene hemiketals and hemiacetals, which were dehydrated by p-toluenesulfonic acid monohydrate or polyphosphonic acid to the corresponding [60]fullerene-fused dihydrofurans. Thus obtained alkyl-substituted and especially unsubstituted [60]fullerene-fused dihydrofurans are difficult to prepare by other methods. The unsubstituted [60]fullerene-fused lactone could react with aliphatic amines to give fullerols.     

Synthesis of disubstituted [60]fullerene-fused lactones: ferric perchlorate-promoted reaction of [60]fullerene with malonate esters

The ferric perchlorate-mediated reaction of [60]fullerene with substituted malonate esters in the presence of acetic anhydride afforded the rare disubstituted [60]fullerene-fused lactones. A possible reaction mechanism is proposed.     

Preparation and aluminum trichloride-induced cationic rearrangements of bicyclo[2.2.0]hexene carboxylic esters

Reaction between the tetramethyl[4]annulene aluminum trichloride σ-complex and α, β-alkenic esters gave the corresponding 1,4,5,6-tetramethylbicyclo[2.2.0]hex-5-one-2-endo-carboxylic esters. AlCl₃-induced cationic rearrangements of these bicyclic esters yielded a number of bicyclo[3.1.0]hexene carboxylic esters and related lactones which were isolated and identified. The isomerization seems to proceed via stereospecific endo protonation and subsequent rearrangement to 2-methoxycarbonyl-1,4,5,6-exo-tetramethylbicyclo(3.1.0]hex-4-yl carbocations.     

Asymmetric intramolecular [2 + 2] photocycloadditions: alpha- and beta-hydroxy acids as chiral tether groups

Chiral alpha- and beta-hydroxy acids such as (S)-lactic acid, (S)-phenyllactic acid, (S)-mandelic acid, or (3R)-3-hydroxybutyric acid have been used as tether groups for intramolecular and diastereoselective [2 + 2] photocycloaddition of 3-oxocyclohexene carboxylic acid derivatives. Total regiocontrol toward the straight adduct and high diastereoselectivities (up to 94%) were observed in the case of butenyl lactate 11. After separation of the two diastereoisomers, cleavage of the chiral tether under basic conditions afforded cyclobutane lactones in good yield and enantiomeric pure form. An X-ray structure has been recorded that confirmed the relative and absolute configuration of the three contiguous stereogenic centers assigned according to CD spectra.     

Direct conversion of esters, lactones, and carboxylic acids to oxazolines catalyzed by a tetranuclear zinc cluster

The tetranuclear zinc cluster Zn4(OCOCF3)6O catalyzes the direct conversion of esters, lactones, and carboxylic acids to oxazolines with remarkable chemoselectivity.     

High-performance CE: an effective method to study lactonization of alpha2,8-linked oligosialic acid

A sensitive and efficient method using high-performance CE (HPCE) and neuraminidase hydrolysis was developed to study the lactonization and hydrolysis of alpha2,8-pentasialic acid. Eleven lactone species of pentasialic acid formed in glacial acetic acid were detected and classified into three groups based on the number of carboxylic acids: monolactones with four carboxylic acids, dilactones with three carboxylic acids, and trilactones with two carboxylic acids. These lactones eluted between the original pentamer (with five carboxylic acids) and the fully lactonized species (with one carboxylic acid) in HPCE. Eight of the isomers were identified by hydrolysis with neuraminodase. Results obtained from previous reports and from this study together reveal a general rule for predicting the subtle difference in the acidity of each carboxylic acid in oligosialic acids: the closer the carboxylic acid is to the nonreducing end, the more acidic it is. Therefore, the elution order of lactone isomers having the same number of carboxylic groups can be predicted from the position of the free carboxylic groups in pentasialic acid. We used this principle and the results of hydrolysis with neuraminidase to identify hexamer lactone isomers separated by HPCE.     

Synthesis of 1, 2-diazabicyclo [2.2.2] octane, 1, 2-diazabicyclo [3.2.1]-octane,and their derivatives

1, 2-Diazabicyclo [2.2.2] octane, its 6-methyl homolog, and 1, 2-diazabicyclo [3.2.1] octane are synthesized by a general method involving nitrosation of piperidine carboxylic acids, subsequent reduction to 1-aminopiperidine carboxylic acids, cyclization to 3-keto-1, 2-diazabicycloalkanes, reduction of the latter to 1, 2-diazabicycloalkanes. A number of 2-substituted 1, 2-diazabicyclo [2.2.2] octanes are synthesized.     

1-[2-(2-hydroxyalkyl)phenyl]ethanone: a new photoremovable protecting group for carboxylic acids

[reaction: see text] A new photoremovable protecting group for carboxylic acids is introduced. The protecting group 1-[2-(2-hydroxyalkyl)phenyl]ethanone, HAPE, is used to protect various carboxylic acids. When photolyzed, the protected compound releases the acid in 70-85% isolated yields. The synthesis and the results of photorelease of the protected acids are presented here.     

Nucleophilic cleavage of lactones and esters with zinc selenolates prepared from diselenides in the presence of Zn/AlCl3

The utility of zinc selenolates for effecting nucleophilic cleavage of simple lactones and esters has been investigated. When zinc selenolate generated via Zn/AlCl₃-promoted cleavage of diselenides was reacted with simple lactones and esters, efficient nucleophilic alkyl-oxygen bond cleavage proceeded generating the corresponding carboxylic acids in moderate to excellent yields.     

Colorimetric determination of organic compounds by formation of hydroxamic acids

Carboxylic acids, their chlorides, anhydrides, esters, lactones, amides, lactams and imides react with hydroxylamine to give hydroxamic acids which are then treated with iron(III). Other compounds or groups of compounds can also be determined after a prior conversion into hydroxylamine-reactive derivatives. The calorimetric applications of these reactions are reviewed. The effect of various factors is discussed. A selective procedure for determination of acid chlorides and anhydrides and an improved procedure for determination of carboxylic esters and lactones are presented.     

Synthesis of α-trifluoromethyl unsaturated acids and derivatives

A one pot synthesis of α-trifluoromethyl unsaturated acids via a [3,3]-sigmatropic rearrangement of allyl (or propargyl) fluorovinyl ethers is described. By proto- and iodolactonization, these acids lead to the corresponding trifluoromethylated lactones.