Supramolecular systems based on cationic surfactants and amphiphilic macrocycles

The effect of the structure of mono- and dicationic surfactants and amphiphilic calixarenes on their aggregation properties, aggregate morphology, and catalytic activity in reactions of nucleophilic substitution in esters is analyzed.     

SILICON-PHOSPHORUS ANALOGIES THE MECHANISM OF NUCLEOPHILIC SUBSTITUTION AT SILICON AND PHOSPHORUS ACTIVATED BY EXTERNAL NUCLEOPHILES EXTENSION OF COORDINATION OF THE REACTIVE SPECIES

Abstract

A comparison is made concerning the mechanism of S_N2 reactions of silicon and phosphorus compounds, catalyzed by nucleophiles. The rate-law of the catalyzed solvolysis of halogenophosphorus esters corresponds to a mechanism with extension of coordination of the reactive species. The overall inversion observed with chlorophosphonates affords a distinction between a nucleophilic activated substitution S_NA (P) and a nucleophilic double displacement at phosphorus.     

Phosphorus stereochemistry : Mechanistic implications of the observed stereochemistry of bond forming and breaking processes at phosphorus in some 5- and 6-membered cyclic phosphorus esters

The stereochemistry of endocyclic and exocyclic bond forming and breaking processes in 5- and 6-membered cyclic phosphorus esters is summarised and comparisons are made with analogous reactions in acyclic phosphorus esters. The factors that determine which bonds are broken and whether reactions occur with inversion or retention of configuration at phosphorus are complex and usually have more obvious effects for reactions in cyclic than in acyclic phosphorus esters ; in particular conformational effects may be important. The stereochemistry of migration of phosphorus ester groups across 1,3-diols is also described. It is suggested that nucleophilic substitutions at phosphorus are inherently stereospecific in the sense that trigonal bipyramidal reaction intermediates break down either directly or following a single Berry Pseudorotation or Turnstile rotation process. Multiple Turnstile rotations which would lead to racemisation, and which apparently do occur in stable phosphoranes, are insignificant for reactions involving trigonal bipyramidal intermediates.     

Dynamic thermodynamic resolution of N-methylpseudoephedrine α-bromo esters for asymmetric syntheses of α-hydroxy carboxylic acid derivatives

An example of dynamic thermodynamic resolution in the nucleophilic substitution reactions of α-bromo esters with an oxygen nucleophile is described. Temperature controlled epimerization-substitution sequence provides a practical protocol for the preparation of highly enantioenriched α-hydroxy carboxylic acid derivatives up to 72% yield with 99:1 er.     

Functionally Substituted Amides and Esters of 3,4,4-Trichloro-3-butenoic Acid

Substituted amides and esters of 3,4,4-trichloro-3-butenoic acid were prepared by reactions of its chloride with appropriate amines and alcohols. Treatment of 3,4,4-trichloro-3-butenomorpholide and tert-butyl 3,4,4-trichloro-3-butenoate results in nucleophilic substitution of the internal chlorine atom with the morpholine residue, accompanied by prototropic allyl rearrangement.     

Nucleophilic substitution at phosphorus: stereochemistry and mechanisms

This review is devoted to the stereochemistry of nucleophilic substitution reactions at phosphorus. The study of the reactions of phosphoryl group transfer is important for biological and molecular chemistry. The stereochemistry and mechanisms of S_N1(P) monomolecular and S_N2(P) bimolecular nucleophilic substitution reactions of organophosphorus compounds are discussed. It has been shown that hydrolysis of many natural phosphates proceeds according to the monomolecular S_N1(P) mechanism via the formation of metaphosphate intermediate (PO₃^?). S_N2(P) nucleophilic substitution at chiral trivalent or pentavalent phosphorus compounds proceeds via the formation of penta-coordinated transition state or pentacoordinate intermediate.     

Correlations of the rate constants of phosphorylation reactions with the empirical parameters of the solvent polarity

Regression analysis of the solvent effects on the rate constants of nucleophilic substitution at the phosphoryl group was performed with the use of the empirical parameters of solvent polarity which characterize the ability of the solvents to electrophilic and nucleophilic solvation. The nucleophilic solvation of reagents by solvents, as a rule, favors the phosphorylation reactions. In the phosphorylation reactions of anionic nucleophiles, the electrophilic solvation of anions influences negatively the reactions rates. The phosphorylation of amines by chlorides of phosphorus acids is facilitated by the electrophilic solvation of a separated anion. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 271–274, February, 1998.     

Micellization properties and the catalytic effect of the aqueous cetyltrimethylammonium bromide-Triton X-100 binary system in nucleophilic substitution in esters of phosphorus acids

The aggregation properties and catalytic effect of the cetyltrimethylammonium bromide-Triton X-100 binary system in nucleophilic substitution in esters of phosphorus acids are studied in the region of normal micelles and oil/water microemulsions. In the presence of phenol, the dissociation of O-alkyl-O-para-nitrophenyl chloromethyl phosphonates is up to 200 times more rapid than the same reaction in water. The efficiency of catalysis depends on the molar ratio of the surfactants and is determined by several factors: concentration, changes in the microenvironment of the reactants, and the shift of the pK _a of phenol.     

A Novel Approach to the Synthesis of Some 2-Aryl Alkanoic Acid Esters

A novel route to the synthesis of some 2-aryl alkanoic acid esters has been achieved. Aromatic nucleophilic substitution of various arene cyclopenta-dienyliron complexes with ethyl ethylacetoacetate and ethyl methylacetoacetate produced the complexed alkanoic acid esters. Photolysis of these complexes resulted in the liberation of the free esters in good yields.     

The effects of sulfur substitution for the nucleophile and bridging oxygen atoms in reactions of hydroxyalkyl phosphate esters

The effects of sulfur substitution on the reactions of hydroxyalkyl phosphate esters are examined. These compounds are models for the intramolecular phosphoryl transfer reaction involved in the cleavage of the internucleotide bond in RNA. The models studied here lack the ribose ring and their conformational flexibility results in greater stability and the availability of different reaction pathways. Sulfur in the nucleophilic position shows no nucleophilic reaction at phosphorus, instead rapidly attacking at the beta carbon atom, forming thiirane with departure of a phosphomonoester. Sulfur substitution at either of the two bridging positions leads to cleavage of the diester via formation of a cyclic intermediate, but with significant rate acceleration when compared to the oxygen analogues. The bridge-substituted models react substantially slower than the analogous ribose compounds with sulfur substitution at comparable positions. Kinetic isotope effects reveal significant differences in the transition state depending on which bridging position sulfur occupies. When sulfur is in the scissile bridging position, a highly associative transition state is indicated, with a largely formed bond to the nucleophile and the scissile P-S bond is little changed. When sulfur occupies the other bridging position, the isotope effects imply a very early transition state in a concerted reaction.     

Kinetics of the reactions of esters and primary amines in “oil-water” type microemulsions

The possibilities of using “oil-water” type microemulsions as a medium for reactions of nucleophilic substitution in esters have been considered. The kinetics of the reactions ofp-nitrophenyl acetate and caprylate with primary amines in the medium indicated has been studied. The hydrophoby factor, being of great importance for micellar solutions of surfactants, is not substantially manifested in detergent microemulsions: the rate constants of the reactions studied are in fact independent of the length of the alkyl radical of the nucleophile.     

Inter- and intramolecular pathways for the formation of tetrahydrofurans from beta-(Phosphatoxy)alkyl radicals. Evidence for a dissociative mechanism

beta-(Phosphatoxy)alkyl radicals generated by photolysis of Barton PTOC esters in the presence of allyl alcohol and tert-butyl mercaptan undergo nucleophilic substitution followed by 5-exo-trig radical ring closure leading to tetrahydrofurans in good yield and with high trans selectivity. beta-(Phosphatoxy)alkyl radicals obtained by intramolecular hydrogen 1,5-abstraction with an alkoxyl radical undergo nucleophilic displacement providing tetrahydrofurans. The ensemble of results, including the effects of leaving groups and substituents, strongly support a dissociative mechanism for these radical nucleophilic displacement reactions.     

Phosphorylation of aminomalonates

The reactions of chloroethynylphosphonates with aromatic secondary aminomalonates occur as classic nucleophilic substitution of chlorine atom at the sp-hybridizied carbon atom to form new phosphorylated 2-arylaminomalonates, diethyl esters of 2-(diethoxyphosphorylethynyl)-2-arylaminomalonic acids. Nonobservance of chemo- and regioselectivity was revealed when using cyclohexyl- and benzylaminomalonates.     

Azidation of anomeric nitro sugars: application in the synthesis of spiroaminals as glycosidase inhibitors

6,5-Fused sugar-derived spiroaminals have been synthesized from the azido esters obtained via the nucleophilic substitution reactions of unstable Michael adducts derived from 1-nitro sugars. Most of the spiroaminals synthesized showed moderate but selective inhibitory activities toward some glycosidases.     

Synthesis and characterization of new 1,1′-diester,diketone, and dinitrile derivatives of 2,2′-biimidazole

Substituted 1,1′-diester, diketone and dinitrile derivatives are prepared from 2,2′-biimidazole. The reactions involved include: Michael addition with halogenated olefins; nucleophilic substitution with ketones, nitriles, and esters; and condensation with amines.     

Dynamic kinetic resolution of α-chloro esters in asymmetric nucleophilic substitution using diacetone-D-glucose as a chiral auxiliary

Diacetone-D-glucose mediated dynamic kinetic resolution of α-chloro-α-aryl esters in nucleophilic substitution reactions has been investigated. Reactions of various amine nucleophiles in the presence of TBAI and DIEA can provide the substitution products 2-10 up to 97% yield and 97:3 dr. This simple procedure with easy removal of the chiral auxiliary provides a practical protocol for asymmetric syntheses of α-amino acid derivatives up to 97:3 er.     

One-Pot Synthesis and Fungicidal Activity of Pyrimidinylidenamido- and Thiazolinylidenamidomonothiophosphoric Esters

A novel one-pot synthesis of four new classes of amidothiophosphoric esters and trisamidothiophosphoric esters is developed. (1-Alkyl-2-pyrimidinylidenamido)bis(diethylamido)thiophosphates, (1-alkyl-2-pyrimidinylidenamido)bis (O-2/4-methylphenyl)thiophosphates, (3-alkyl-2-thiazolinylidenamido)bis (diethylamido)thiophosphate and (3-alkyl-2-thiazolinylidenamido)bis(O-2/4-methylphenyl)thiophosphates are obtained from the nucleophilic substitution and oxidation of N-alkyl-2-cycloiminylidenaminodichlorophosphines generated in situ from the reaction of the corresponding N-alkyl-2-aminocycloiminium halide with phosphorus trichloride and triethylamine. The synthesized thiophosphoric esters have been investigated for fungicidal properties.     

有机磷化合物的研究 X:五价膦(磷)酸酯与卤代烷在卤化钠存在下的酯烷基交换反应

A detailed study on the ester alkyl exchange reaction of various types of quinique-valent phosphorus esters with alkyl halide in the presence of sodium bromides was reported. This ester alkyl exchange reaction was evidently influenced by the structure of phosphorus esters and alkyl halides as well as by the nature of the halides of metal ions. In contrast with the reaction without sodium hadlide, the alkyl phosphinmate is more reactive than phosphonate and phosphate by treatment with alkyl halide in the presence of sodium halide. This is consistent with the high nucleophilicity of >P(CO)O- as leaving group. The reactivity of butyl halides was decreased in the following order: n-BuBr>i-BuBr=s-BuBr>t-BuBr. Alkyl iodide was proved to be more reactive than the corresponding bromide and chloride. However, the use of iodioe is limited by the formation of alkene resulted from the elimination of HI. These structural effects show the general characteristics of a nucleophilic substitution reaction. A reaction mechanism involving the formation of sodium salt intermecutiate was proposed based on the concept of HSAB principle. This reaction may, however, be used as a convenient method for the preparation of mixed esters of quinque-valent phosphorus acids.     

Unusual reactivity patterns in bis-triphenylalkoxyphosphonium salts

Alkoxyphosphonium triflates have been prepared and reacted with a number of nucleophiles. Only negatively charged nucleophiles initiate substitution reactions. Nucleophile association with the phosphorus entity, prior to nucleophilic displacement, is implied.     

Stereoselective reactions of trivalent phosphorus compounds

The data on stereoselective reactions of achiral compounds of trivalent phosphorus with chiral nucleophiles (derivatives of secondary alcohols, amines, and amino acids) are analyzed and discussed. In certain cases, these reactions enable preparation of optically active aminophosphines and phosphinites, precursors in the synthesis of chiral organophosphorus compounds and phosphine ligands. The reactions are suitable for elucidation of mechanism and stereochemistry of nucleophilic substitution at trivalent phosphorus atom.