Kiah H. Ang

The synthesis of oxazoles by thermolysis or photolysis of 2-acylisoxazol-5-ones

Abstract N-acylisoxazol-5-ones are converted into the corresponding 2-substituted oxazoles by photolysis at 300 or 254nm, or by flash vacuum pyrolysis. The former procedure is favoured for isoxazolones with electron withdrawing groups at C-4, and pyrolysis for all others.

Incorporation of 2-hydroxy-4-methoxybenzyl protection during peptide synthesis via reductive alkylation on the solid phase

Abstract A method has been developed for the synthesis of Hmb protected amino acid residues via reductive alkylation of 2-hydroxy-4-methoxybenzaldehyde with resin bound amino acids/peptides. The methodology potentially allows incorporation of Hmb protected amino acids at any point in the synthesis of difficult peptides. Synthesis of ACP (65–74) illustrates the method.

The Chemistry of 5-Oxodihydroisoxazoles. XIII. Reactions of the Imino Carbene Derived From Photolysis of Ethyl 5-Oxo-2-phenyl-2,5-dihydroisoxazole-4-carboxylate

Photolysis of ethyl 5-oxo-2-phenyl-2,5-dihydroisoxazole-4-carboxylate at 300 nm in acetonitrile gives a carbene which is captured efficiently by bromide, chloride, acetate and cyanate, and less efficiently by iodide, thiocyanate, cyclohexene and tetrahydrofuran. No hydrogen abstraction or reaction with double bonds was evident.

NOVEL METHOD FOR THE LOADING OF NUCLEOPHILES ON MULTIPIN CROWNS

Abstract We have developed a useful method for the loading of various nucleophiles such as anilines and phenols onto Multipin Crowns containing the Rink linker, which cannot be readily attached by other methods. The product of the reaction was confirmed using Magic Angle Spinning NMR.

The photolysis of ethyl 5-oxo-2-phenyl-2,5-dihyroisoxazole-4-carboxylate in amines and alcohols

Abstract Ethyl 5-oxo-2-phenyl-2,5-dihydroisoxazole-4-crboxylate(1) has been photolysed at 300 nm in a variety of alcohols and amines. The products suggest two competing photolytic pathways: reversible photoisomerisation to a ketene, and a loss of carbon dioxide to form a singlet imino-carbene.

The Chemistry of 5-Oxodihydroisoxazoles. XII. Trapping of Derived Ketenimines With Lithium Amides and Alkyllithiums

Isoxazolones unsubstituted at C3 react with lithium amides or alkyllithiums to give ketenimines . The presence of an ethoxycarbonyl group at C4 allows capture of this species by addition of a second equivalent of the lithiated species to give enolates which can be alkylated in situ. The presence of a phenyl group at C4 gives a ketenimine which reacts intramolecularly in the presence of lithium amides, whereas alkyllithiums undergo addition in synthetically useful processes.

Triplet Lifetimes, Solvent, and Intramolecular Capture of Isoxazolones

The first step in the photochemical decarboxylation of isoxazolones is the formation of the triplet state of the isoxazolone. We present evidence for the first time from flash laser photolysis of the lifetime of such species, and examples of their capture by solvent and by intramolecular cycloaddition.