Sunit Thianpatanagul

X=Y-ZH systems as potential 1,3-dipoles. Part 21 activation of the ZH proton in imines.

Abstract A range of substituents is capable of inducing thermal 1,3-dipole formation in imines by activation of the CH proton as shown by trapping experiments with dipolarophiles.

Decarboxylative transamination. A new route to spirocyclic and bridgehead-nitrogen compounds. Relevance to α-amino acid decarboxylases

N-Substituted and α,α-disubstituted amino acids react with carbonyl compounds to generate 1,3-dipolar species under mild conditions mimicking α-amino acid decarboxylases; the 1,3-dipoles can be trapped both inter- and intra-molecularly to give bridgehead-nitrogen and spirocycli products in goood yield; pyridoxal is shown to react in an analogous fashion.

XY–ZH systems as potential 1,3-dipoles. Part 11. Stereochemistry of 1,3-dipoles generated by the decarboxylative route to azomethine ylides

The decarboxylative reaction of aryl aldehydes with cyclic secondary α-amino acids or primary α-amino acids in the presence of N-methyl- or N-phenyl-maleimide leads, via an intermediate azomethine ylide, to mixtures of bicyclic pyrrolidine cycloadducts in good yield. Cyclic secondary α-amino acids, where the carboxylic group is non-benzylic, give cycloadducts arising from a stereospecifically generated anti-dipole. Acyclic α-amino acids, and cyclic secondary α-amino acids with the carboxylic group located at a benzylic site, give rise to cycloadducts derived from both anti- and syn-configurations of the intermediate azomethine glides. The reactions show little discrimination between endo- and exo-transition states for the cycloadditions.

X=Y-ZH systems as potential 1,3-dipoles. Activation of the ZH proton in imines

Abstract A range of substituents is capable of inducing thermal 1,3-dipole formation in imines by activation of the CH proton as shown by trapping experiments with dipolarophiles.

X=Y-ZH compounds as potential 1,3-Dipoles. Part 231,2 mechanisms of the reactions of ninhydrin and phenalene trion with ∝-amino acids. X-ray crystal structure of protonated ruhemann's purple, a stable azomethine ylide

Abstract The ninhydrin reaction is shown to involve stereospecifically formed azomethine ylides of two types by trapping of the intermediates with maleimides as dipolarophiles. One type of azomethine ylide, in which the carboxyl group of theoriginal ∝-amino acid is retained, is probably only important for glycine. The other type of azomethine ylide does not contain a carboxyl group and is formed from all ninhydrin positive ∝-amino acids via decarboxylative cycloreversion of an oxazolidin-5-one precursor. Phenalene-1,2,3-trione reacts with ∝-amino acids via a different mechanism despite the formal similarity of the two reagents. In this case decarboxylation occurs in a carbinolamine and azomethine ylides are not involved. An X-ray crystal structure of protonated Ruhemanns Purple shows it to be a stable N-H azomethine ylide, confirming the results of cycloaddition studies.

X=Y-ZH systems as potential 1,3-dipoles. Cycloadditions of thiominoethers and thioiminocarbonates

Abstract Thioiminoethers and thioiminocarbonates of α-amino acid esters undergo acetic acid catalysed cycloaddition reaction with N-phenylmaleimide via their 1,3-dipolar tautomers.

X=y-zh systems as potential 1,3-dipoles : Part 22.1 cycloaddition reactions of pyridoxal imines. relevance to a-amino acid racemases and transaminases.

Abstract Pyridoxal imines of ∞-amino acid esters and related amines undergo cycloaddition to N-phenylmaleimide on heating in acetonitrile, toluene or xylene. The cyclo-additions proceed in good yield, are stereospecific, and involve an endo-transition state. The reactive intermediates are postulated to be NH azomethine ylides produced stereospecifically from the imines by prototropy.

Decarboxylative transamination. Mechanism and applications to the synthesis of heterocyclic compounds

The currently accepted mechanism for decarboxylative transamination is shown to be incorrect; the intervention of 1,3-dipolar species in the decarboxylative transamination of α-amino acids is demonstrated by trapping with a range of dipolarophiles.

XY–ZH systems as potential 1,3-dipoles. Part 6. Metallo-1,3-dipoles. Cycloadditions of divalent metal complexes of glycine and alanine imines to electronegative olefins

Copper(II), zinc(II), and cadmium(II) complexes of imines derived from α-oxo acids and glycine or alanine undergo stereospecific cycloaddition at room temperature to 1,2-disubstituted electronegative olefins in the presence of weak base. Corresponding reactions of lead(II) complexes give insoluble cycloadducts. In contrast, the reactions of the same metallo imines with methyl acrylate, phenyl vinyl sulphone, and acrylonitrile frequently give mixtures of regio- and stereo-isomers. These mixtures are shown to arise by stereoisomerisation of initial cycloadducts formed by a 4π+ 2π concerted cycloaddition of intermediate metallo-1,3-dipoles.

Cycloaddition reaction relevant to the mechanism of the ninhydrin reaction. X-Ray crystal structure of protonated Ruhemann's purple, a stable 1,3-dipole

Trapping experiments with dipolarophiles provide evidence for the formation of 1,3-dipoles as interemediates in the ninhydrin reaction and protonated Ruhemanns purple is shown to be a stable N-protonated 1,3-dipole by trapping experiments and by an X-ray crystal structure determination.