Camphor derivatives as chiral auxiliaries in asymmetric synthesis

Electron impact fragmentation patterns of 3,3-dimethyl-1, 2-norbornane derivatives

The electron impact mass spectra of several 3,3-dimethyl-1, 2-norbornanediols, diamines, amino alcohols and related derivatives have been studied and their fragmentation pathways discussed. Different fragmentation patterns were observed, depending not only on the nature of the substituents, but also on their relative positions on the norbornane framework. In general, the dominant peaks in the spectra of these compounds originate from initial C1-C2 bond cleavage (alpha-cleavage) with charge retention on the heteroatom (oxygen or nitrogen) attached at the bridgehead position, followed by hydride shift and loss of the C2-C3 fragment by homolytic cleavage of the C3-C4 bond. This fragmentation pathway leads to a highly stabilized cyclopentenylimmonium or cyclopentenyloxonium ion, which constitutes the base peak in the spectra in most of the studied compounds. Copyright 1999 John Wiley & Sons, Ltd.

Diastereoselective Conjugate Addition to (+)-Camphorsulfonic Acid Derived Nitroalkenes: Synthesis of alpha-Hydroxy and alpha-Amino Acids

Diastereoselective tandem conjugate addition of both oxygen- and nitrogen-centered nucleophiles to the novel (1S)-10-camphorsulfonic acid derived nitroalkenes 9, 10, and 11 and ozonolysis gave the alpha-hydroxy and alpha-amino thiol acid derivatives 12, 13, and 14. In all cases, the (R)-diastereomer was formed as the major component albeit with only modest levels of selectivity (33-71% de). The structures of the products and the stereochemistry of the Michael addition step were unequivocally established by X-ray crystallographic studies of nitroalkenes 9 and 10 and (2S)-12c and (2R)-13a and by alternative syntheses from (S)-alanine, (S)-valine, and ethyl (S)-lactate.

Investigation of Dienophile-TiCl(4) Complexation by Means of X-ray Absorption and (13)C-NMR Spectroscopies

Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) techniques, in combination with (13)C-NMR spectroscopy, have been used to study the complexation of methyl acrylate (1), N-acryloylbenzylamine (2), O-acryloyl-(R)-pantolactone (3), methyl N-acryloyl-(S)-prolinate (4), and methyl N-acryloyl-(S)-phenylalaninate (5) with excess TiCl(4) in solution. The results obtained show that TiCl(4) has a great tendency to coordinate with two ester ligands, but this tendency is not so marked with amides, which is related to the greater basicity of the latter. Complexation increases the Ti-Cl bond distance, in comparison with TiCl(4), which is clearly shown by the EXAFS spectra. Chelate complexes are formed with bidentate ligands, but comparison between the EXAFS spectra, obtained with different TiCl(4)/dienophile ratios, shows that chelation is more difficult with methyl N-acryloyl-(S)-phenylalaninate (5).

Synthesis of 2-isoxazoline and alpha-hydroxy ketomethylene dipeptide isosteres

We have developed a simple and stereoselective method for synthesizing novel dipeptide isosteres using nitrile oxide cycloaddition as a key reaction. Employing this method, we have prepared efficiently various peptidomimetics containing 2-isoxazolines and alpha-hydroxy ketomethylene dipeptide isosteres.

ASYMMETRIC DIELS-ALDER REACTION : CIS-1-ARYLSULFONAMIDO-2-INDANOLS AS HIGHLY EFFECTIVE CHIRAL AUXILIARIES

Lewis acid promoted Diels-Alder reaction of acrylate esters of cis-1-arylsulfonamido-2-indanols and cyclopentadiene provided exclusively endo-adducts with high endo-diastereoselectivities.