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PubMed2001

A facile and highly diastereoselective aziridination of chiral camphor n-enoylpyrazolidinones with n-aminophthalimide.

Reaction of various chiral camphor N-enoylpyrazolidinones 2a-g with N-aminophthalimide in the presence of lead tetraacetate in CH(2)Cl(2) proceed smoothly afford the corresponding N-phthalimidoaziridines (3a-e, 4f-g) with excellent material yields (86-95%) at room temperature in 5 min. High levels of diastereoselectivities (up to >95:5 dr) were obtained. The solvent effect was investigated, and the auxiliary can be easily recovered in high yields under mild reaction conditions.

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PubMed2001

Dynamic kinetic resolution of beta-azido alcohols. An efficient route to chiral aziridines and beta-amino alcohols.

Enzymatic resolution of beta-azido alcohols in combination with ruthenium-catalyzed alcohol isomerization led to a successful dynamic kinetic resolution. A variety of racemic beta-azido alcohols were efficiently transformed to the corresponding enantiomerically pure acetates (ee up to 99% and conversion up to 98%). The synthetic utility of this procedure has been illustrated by the practical synthesis of (S)-propanolol I and (R)-beta-azido-alpha-(4-methoxyphenyl)ethanol ((R)-1c), a direct precursor of denopamine II.

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PubMed2005

Aziridines versus vinyl carbamates from the direct amination of electron-withdrawing group-substituted trifluoromethyl enoates.

Aza-MIRC (Michael-initiated ring closure) and C-H insertion products were obtained in the reactions of trifluoromethylated olefins with different nosyloxycarbamates by changing base and solvent. Aza-Michael addition products were not isolated. The presence and the position of the trifluoromethyl group allow control of the outcome of the reactions.

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PubMed1996

Photolysis of Matrix-Isolated 4-R-1,2,4-triazoline-3,5-diones: Identification of Aziridine-2,3-dione Transients.

Matrix-isolated 4-methyl-1,2,4-triazolinedione 1a and 4-phenyl-1,2,4-triazolinedione 1b were photolyzed at lambda >/= 335 nm and lambda >/= 310 nm, respectively. The reactions induced by photolysis were monitored by FT-IR spectroscopy. The isocyanates 2a and 2b are always the more abundant products with carbon monoxide. Methyl- and phenylaziridine-2,3-diones (3a and 3b) were detected as minor, but well-identified reaction products. The IR experimental absorption bands were assigned by comparison with literature data and with simulated infrared spectra obtained by ab initio calculation at the 6-31G level. Stable at the matrix temperature (10 K), 3a and 3b photolyzed to isocyanates and CO when irradiated at lambda >/= 230 nm. Irradiation of 2b at this wavelength induces its decomposition. The kinetic data show that the rate constant process 1a --> 2a is faster than the 1a --> 3a process (3.29 x 10(-)(3 )and 2.35 x 10(-)(4)min(-)(1) respectively).

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PubMed1997

Palladium(0)-Catalyzed Isomerization Reactions of Aziridines Bearing an alpha,beta-Unsaturated Ester Group: A Thermodynamic Preference for Chiral Alkyl (2E)-4,5-cis-4,5-Epimino-N-(alkyl- or arylsulfonyl) 2-Enoates over the Other Three Stereoisomers.

Palladium(0)-catalyzed reactions of five sets of four stereoisomeric 4,5-epimino-N-(methanesulfonyl) or -N-(arylsulfonyl) 2-enoates reveal that 4,5-cis-(2E)-isomers are thermodynamically more stable than other isomers, in accord with calculations. A highly stereoselective synthesis of (E)-alkene dipeptide isosteres having the desired stereochemistries from unwanted stereoisomeric 4,5-epimino-N-(arylsulfonyl) 2-enoates is also presented.

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