A biomimetic approach to the pyoverdin chromophore

Pyoverdins are siderophores which chelate with ferric ions forming a ligand complex. Pyoverdins are excreted from bacteria such as Pseudomonas, for example, Pseudomonas fluorescens, when grown in iron-deficient conditions, to scavenge for iron. Although, different species of Pseudomonas produce different pyoverdins with various constituents in their amino acid chains, they all share a common chromophore structure within the various natural siderophores. The possible biosynthesis of the pyoverdins chromophore is discussed. Herein a biomimetic synthesis of a model of the chromophore unit based on an oxidative cyclisation pathway was carried [out]. [Continues.

Improving catalyst activity in secondary amine catalysed transformations

The effect on catalyst performance of altering substituents at the 2-position of the Macmillan imidazolidinone has been examined. Condensation of L-phenylalanine N-methyl amide with acetophenone derivatives results in a series of imidazolidinones whose salts can be used to accelerate the Diels-Alder cycloaddition. Electron withdrawing groups significantly increases the overall rate of cycloaddition without compromise in selectivity. The most effective catalyst was shown to be efficient for a variety of substrates and the applicability of this catalyst to alternative secondary amine catalysed transformations is also discussed

Organocatalytic α-oxybenzoylation of aldehydes

A simple method for the asymmetric α-oxybenzoylation of aldehydes is presented. Treatment of a series of aldehydes with benzoyl peroxide in the presence of a MacMillan imidazolidinone leads directly to the α-oxybenzoylated product with excellent levels of asymmetric induction

Readily accessible chiral at nitrogen cage structures

The reaction of glycine-N-methyl amide with paraformaldehyde in the presence of ytterbium triflate (1 mol%) leads to a novel cage structure 6 which is chiral at nitrogen. Single crystal X-ray analysis and DFT calculations suggest this cage structure is rigid and adopts a single low energy conformation. Use of single enantiomer α-amino amides results in two diastereomeric tertiary amines that differ in their absolute configuration at nitrogen. These diastereoisomers interconvert under acidic conditions but are configurationally stable under basic conditions and can be readily separated by either crystallisation or column chromatography. By reacting racemic chiral α-amino amides a third diastereomeric cage can also be isolated through this reaction protocol. Preparation of mixed cages by reacting two different α-amino amides is also possible allowing for greater structural diversity in the products to be attained. Preliminary mechanistic studies show that all three methylene units in the cage structure are labile and can be replaced under acidic reaction conditions

Direct α-oxytosylation of carbonyl compounds : one-pot synthesis of heterocycles

N-Methyl-O-tosylhydroxylamine (I) is an effective reagent for the direct α-oxytosylation of carbonyl compds. The reactions proceed smoothly at room temp. in the presence of both moisture and air and functional group tolerance in the substrate is good. With nonsym. substrates, regioselectivity for primary over secondary centers is obsd. and complete regiospecificity for primary over tertiary centers is obtained. E.g., reaction of I and PhCOCH2CH3 gave 48% PhCOCHMeOTs. Addn. of a bis-heteronucleophile directly to the crude reaction mixt. in a one-pot process leads to the corresponding heterocyclic product. E.g., reaction of I and acetone, followed by addn. of H2NCSPh, gave 69% 4-methyl-2-phenylthiazole. [on SciFinder(R)

The direct formation of α-carbamates from carbonyl compounds

A simple one-pot method for the direct introduction of carbamates α to carbonyl groups that proceeds at room temp. in the presence of both moisture and air was developed. Treatment of aldehydes and both cyclic and acyclic ketones with N-methyl-O-carbamoyl hydroxylamine hydrochlorides provides the α-functionalized products in 50-88% isolated yield. The transformation is tolerant of a range of functional groups within the substrate and is also effective for the introduction of a variety of oxycarbamoyl groups

The direct introduction of carbonates α to carbonyl groups

The first method for the direct formation of α-oxycarbonates from both aldehydes and ketones is described. N-Methyl-O-alkoxyformate hydroxylamine hydrochloride reagents can be prepd. in two high-yielding steps from N-Boc-N-methylhydroxylamine and were found to be bench stable. These were reacted with a variety of carbonyl compds. to give the corresponding α-functionalized products in 48-98% isolated yield via a proposed [3,3]-sigmatropic rearrangement