Aravamudan S. Gopalan

Facile esterification of sulfonic acids and carboxylic acids with triethylorthoacetate

Triethylorthoacetate was found to be surprisingly more effective than triethylorthoformate in the esterification of sulfonic acids and carboxylic acids. Using this reagent, esters of sulfonic and carboxylic acids are prepared in high yields.

Synthesis and metal ion complexation properties of a novel polyethyleneimine N-methylhydroxamic acid water soluble polymer

A major goal of our research program is to develop water soluble chelating polymers for the selective separation of trivalent cations such as iron(III) and tetravalent actinide ions such as Th(IV) or Pu(IV) from aqueous, radioactive waste streams. As part of this effort, we have synthesized a new water soluble polyethyleneimine polymer that incorporates N-methylhydroxamic acid chelating groups. Both the synthesis of this chelating polymer, PEI-NMH, and its ability to achieve selective separation of target metal ions using ultrafiltration will be discussed. It is interesting to note that the PEI-NMH polymer selectively binds iron(III) over thorium(IV) at pH 1 in contrast to its primary hydroxamate analog PEI-H. The binding properties of these polymers have been evaluated using both potentiometric and spectrophotometric methods. A comparison of the binding properties of PEI-NMH and PEI-H reveals the importance of the nature of the ligand in the complexation process.

Chiral γ and δ Hydroxysulfones via lipase catalyzed resolutions - synthesis of (R)(+)-4-hexanolide and (2R,5S)-2-methyl-5-hexanolide using intramolecular acylation

Abstract Lipas PS-30 (Amano) was found to be an effective catalyst for enantioselective transesterification of a number of racemic γ and δ hydroxysulfones with isopropenyl acetate in ether. The intramolecular acylation of the ethyl carbonate derivatives obtained from the chiral hydroxysulfones 1d and 1b has been used for the preparation of R (+)-4-hexanolide, sex pheromone of the female dermestid beetle Trogoderma glabrum and (2 R , 5 S )-2-methyl-5-hexanolide, the sex pheromone of the carpenter bee.

Chiral non-racemic dihydroxysulfones via hydrolytic kinetic resolutions—synthesis of oxacyclic ring systems using intramolecular acylation strategies

Abstract A number of chiral non-racemic 1,2-dihydroxysulfones have been prepared in good yields and high enantiomeric excesses by hydrolytic kinetic resolution of the corresponding epoxysulfones with Jacobsens (S,S)-salen(Co)III(OAc) catalyst. The intramolecular cyclization reactions of the acyl and ethoxycarbonyl derivatives of these dihydroxysulfones have been exploited to access a variety of functionalized chiral non-racemic cyclic ethers and lactones in good yields.

Polyene cyclizations using mercury (II) triflate-N,N-dimethylaniline complex - participation by internal nucleophiles

Abstract The cyclization of a number of functionalized polyenes with mercuric triflate - N,N-dimethylaniline complex (Nishizawas reagent) to give bicyclic or tricyclic products has been studied. Suitably positioned internal nucleophiles, such as carbonyl, hydroxy and β-ketoester groups were found to participate to varying extent, in the termination of these cyclizations.

Syntheses of some new polyaminocarboxylate and CMPO calix[4]arene chelators for the selective extraction of actinide ions

The syntheses of two new calix[4]arene derivatives designed for the selective liquid-liquid extraction of actinide ions have been achieved. The first, is a novel organic soluble calix[4]arene chelator 2 having four iminocarboxylate ligand moieties anchored to the lower rim. The second calix[4]arene derivative 3 that has been readily synthesized has four CMPO ligand groups tethered to the lower rim. Preliminary studies show that both 2 and 3 extract thorium(IV) more efficiently than europium(III) under acidic conditions into chloroform.

Convenient method for the preparation of some polyhydroxamic acids : Michael addition of amines to acrylohydroxamic acid derivatives

Reagents 1, 2, and 3 are readily prepared by the reaction of the appropriate hydroxylamine derivatives with acryloyl chloride. They undergo Michael addition with a variety of amines to give the corresponding O-protected hydroxamate derivatives in moderate to good yields. Subsequent removal of the protecting group provides a convenient method for the preparation of a number of mono, di, tri and tetrahydroxamic acids.

Synthesis of Symmetrical Methylenebis(Alkyl Hydrogen Phosphonates) by Selective Cleavage of Methylenebis(Dialkyl Phosphonates) with Morpholine

Abstract The preparation of partial esters of methylenebisphosphonic acids has been of recent interest due to their potential therapeutic applications. This paper describes a convenient method to prepare symmetrical methylenebis(alkyl hydrogen phosphonates) by the selective cleavage of the corresponding methylenebis(dialkyl phosphonate) with refluxing morpholine. The effects of structural variations on the amine as well as the substrate have been investigated to understand the scope and limitations of this reaction. A superior approach to hindered bisphosphonic acid esters involves the cleavage of their dimethyl esters, 4, using morpholine. This method is also useful to access a number of C-alkyl dialkyl methylenebisphosphonic acids such as 6. This study clearly shows that cleavage with morpholine is convenient, inexpensive, and allows for the preparation of a variety of P,P′-disubstituted partial esters in good yields and high purity.

Reactions of N-Benzyloxycarbamate Derivatives with Stabilized Carbon Nucleophiles: A New Synthetic Approach to Polyhydroxamic Acids and Other Hydroxamate-Containing Mixed Ligand Systems†

Hydroxamic acids are an important class of chelators of hard metal ions such as Fe(III), which have found applications in therapeutic, diagnostic, and separation chemistry. Hence, methods for their preparation and incorporation into various matrices are important. A new strategy for the preparation of hydroxamic acids that uses readily available N-benzyloxy carbamic acid ethyl ester, 1, has been developed. N-Alkylation of 1 occurs readily to give N-alkyl-N-benzyloxy carbamates, 2, which react with a variety of stabilized carbon nucleophiles to give functionalized protected hydroxamic acids, 3, in good to excellent yields. The O-protected hydroxamate intermediates 3 can be further alkylated with halides to access a variety of potential metal binding hosts. The usefulness of this methodology has been demonstrated by the synthesis of a novel trihydroxamic acid 6, mixed ligand systems 9 and 12, and the macrocyclic dihydroxamic acid 16.

Bakers' Yeast Reduction of γ and δ Ketonitriles: Intermediates for the Synthesis of (S)-5-Hexanolide and Other Chiral Lactones

Abstract A number of γ and δ ketonitriles have been synthesized and their reduction with bakers yeast carefully studied. Both 4-oxopentanenitrile and 5-oxohexanenitrile are reduced in moderate yields to the corresponding (S) alcohols of high ee while other substrates gave products of varying optical purities. These alcohols are useful intermediates for the preparation of chiral lactones, including the synthetically important (S)(−)-4-methylbutyrolactone and (S)-(−)-5-hexanolide.