Membrane transport of dicarboxylic and α-hydroxy carboxylic acids induced by α-amino phosphonates

New -amino phosphonates containing different alkyl and aryl substituents at the -carbon atom were synthesized in high yields by the Kabachnik—Fields and Pudovik reactions. These compounds were studied as carriers of several -hydroxy carboxylic and dicarboxylic acids through liquid impregnated membranes. These -amino phosphonates studied are capable of molecular recognition of oxalic acid among structurally similar -hydroxy carboxylic and dicarboxylic acids. The efficiency and selectivity of mass transfer of oxalic acid increase with an increase in the lipophilicity of the -amino phosphonate.     

An organocatalyzed facile and rapid access to α-hydroxy and α-amino phosphonates under conventional/ultrasound technique

In the present work, successful implementation of ultrasound irradiation for the rapid synthesis of α-hydroxy and α-amino phosphonates under solvent-free conditions is demonstrated. Use of a novel catalyst (i.e., camphor sulfonic acid) in combination with ultrasound technique is reported for the first time. Comparative study for the synthesis of α-hydroxy and α-amino phosphonates using conventional as well as ultrasonication method is discussed.     

Mechanistic approach for expeditious and solvent-free synthesis of α-hydroxy phosphonates using potassium phosphate as catalyst

An extremely simple, high yielding, highly rapid and solvent-free protocol has been described for hydrophosphylation of aldehydes using potassium phosphate as catalyst. Easy commercial availability of the reusable catalyst, operational simplicity at ambient temperature and avoidance of conventional work-up as well as purification procedure makes this solvent-free protocol a near-ideal synthesis.     

Organocatalytic synthesis of α-hydroxy and α-aminophosphonates

A new and highly flexible procedure is described for the synthesis of α-amino- and α-hydroxy phosphonates. In the presence of a catalytic amount of oxalic acid (10 mol %), trimethyl phosphite reacts with aldehydes or imines (generated in situ from an aldehyde and an amine) to yield the corresponding coupled products in good yield.     

Efficient synthesis of β-lactam containing α-hydroxy phosphonates using tartaric acid and fumaric acid as mild catalysts

A short and efficient protocol for the synthesis of β-lactam containing α-hydroxy phosphonate esters using inexpensive catalysts such as tartaric acid and fumaric acid is described.     

The first synthesis of β-amino phosphonates using cyclic sulfamidates

Cyclic sulfamidates (prepared from α-amino acids and β-amino alcohols) have been used for the first time for the synthesis of novel β-amino phosphonates (chiral and achiral) by treatment with dialkyl phosphites using sodium hydride. 2-Substituted and 1,2-disubtituted β-amino phosphonates have efficiently been prepared following this method. The products are formed in high yield (79-84%) within 8-12 h.     

Synthesis of cyclic α-amino ketones

Summary A simple method is described for synthesizing cyclic -amino ketones by intramolecular cyclization of azlactones under the action of aluminum chloride.     

Asymmetric α-oxyacylation of cyclic ketones

Reaction of cyclic ketones with chiral N-alkyl-O-acyl hydroxylamines leads to the corresponding α-oxyacylated carbonyl compound in up to 89% ee. The levels of asymmetric induction were influenced by solvent polarity, acid strength and, to a lesser extent, temperature. Increasing the steric bulk around the nitrogen atom of the hydroxylamine reagent led to increased levels of asymmetric induction, which was also found to be detrimental to the yield observed for the transformation. Examination of N- and O-substituents along with substrates revealed the scope and limitations of the procedure.     

Absolute configurational assignment of α-hydroxy acids and α-hydroxy esters from their Cupra A circular dichroism spectra

The in situ formed complexes of cuprammonium solution (Cupra A) with optically active α-hydroxy acids and α-hydroxy esters show circular dichroism spectra suitable for determination of the absolute configuration of both groups of compounds. In the long wavelength spectral region, compounds of R configuration at the α carbon atom display a positive Cotton effect of around 600 nm and a negative one at ca. 720 nm, whereas (S)-α-hydroxy acids and esters exhibit negative and positive Cotton effects, respectively, in the same spectral range.     

Synthesis of α-hydroxy(polyprenyl) bisphosphonates

Bisphosphonates derived from natural terpenes were synthesized by phosphonylation of corresponding aldehydes. The general strategy of introduction of the phosphonate groups into the polyprenol molecule involves successive treatment of a hydroxyl compound by Swern reagent to oxidize the C-OH group into C=O and a (EtO)₃P/[PyH]⁺ClO _? ⁴ mixture to phosphylate the resulting carbonyl compound.     

Electrophilic asymmetric syntheses of α-hydroxy carboxylic acids

Asymmetric electrophilic synthesis of α-hydroxy carboxylic acids from chiral amide derivatives of tert-butyl- and trialkylsilyl- protected glycolic and lactic acids are described which lead to chiral α-hydroxy carboxylic acids in 60–95% diastereomic excess.     

Enantioselective organocatalytic α-fluorination of cyclic ketones

The first highly enantioselective α-fluorination of ketones using organocatalysis has been accomplished. The long-standing problem of enantioselective ketone α-fluorination via enamine activation has been overcome via high-throughput evaluation of a new library of amine catalysts. The optimal system, a primary amine functionalized Cinchona alkaloid, allows the direct and asymmetric α-fluorination of a variety of carbo- and heterocyclic substrates. Furthermore, this protocol also provides diastereo-, regio-, and chemoselective catalyst control in fluorinations involving complex carbonyl systems.     

A simple protocol for the synthesis of α-substituted phosphonates

An efficient, easy-to-handle, and mild substitution reaction approach has been developed for the synthesis of phosphonate derivatives, which are very important in the field of industrial, agricultural, and medicinal chemistry. A large number of nucleophiles, including arylamines, alkylamines, heteroarylamines, primary amines and secondary amines, sulfides, and carbides were attempted to react with α-tosyloxyphosphonate 1. The reaction proceeded under catalyst-free and neat conditions and the corresponding phosphonates 2 were afforded in good yields.     

Oxidation of enamines to α-hydroxy ketones and α-amino ketones using N-sulfonyloxaziridines

Tri-substituted enamines are oxidized to α-hydroxy ketones by N-sulfonyloxaziridines while di-substituted enamines are oxidized to α-amino ketones. A unified mechanism for the formation of both α-hydroxy ketones and α-amino ketones is proposed.     

Rate constants for cyclizations of α-hydroxy radical clocks

The 1-hydroxy-1-methyl-6,6-diphenyl-5-hexenyl radical (4a) and the 1-hydroxy-1-methyl-7,7-diphenyl-6-heptenyl radical (4b) were prepared from the corresponding PTOC esters (anhydrides of a carboxylic acid and N-hydroxypyridine-2-thione). The key step in the synthetic method for the precursors was a coupling reaction of the respective carboxylic acids with the thiohydroxamic acid, which was conducted for ca. 5 min and followed rapidly by chromatography. Rate constants for cyclizations of radicals 4a and 4b in acetonitrile and in THF were measured directly between -30 and 60 °C by laser flash photolysis methods. The Arrhenius functions in acetonitrile are log k = 9.9-2.6/2.303RT and log k = 8.9-4.4/2.303RT (kcal mol(-1)) for 4a and 4b, respectively. Rate constants for cyclizations at room temperature of 9 × 10(7) s(-1) and 4 × 10(5) s(-1) are somewhat larger than the rate constants for cyclizations of analogous alkyl radicals. Crude rate constants at room temperature for H-atom trapping of 4a by thiophenol and 4b by t-butylthiol were k(T) = 1.2 × 10(9) M(-1) s(-1) and k(T) = 2 × 10(7) M(-1) s(-1), respectively, which are modestly larger than rate constants for reactions of alkyl radicals with the same trapping agents.     

Facile synthesis of α-hydroxy carboxylic acids from the corresponding α-amino acids

An effective and improved procedure is developed for the synthesis of α-hydroxy carboxylic acids by treatment of the corresponding protonated α-amino acid with tert-butyl nitrite in 1,4-dioxane–water. The amino moiety must be protonated and located α to a carboxylic acid function in order to undergo initial diazotization and successive hydroxylation, since neither β-amino acids nor acid derivatives such as esters and amides undergo hydroxylations. The method is successfully applied for the synthesis of 18 proteinogenic amino acids.