Chiral Magnesium Research Articles

Enantioselective Diels-Alder reactions catalyzed by chiral magnesium lewis acids prepared from hydroxysulfoxides

Enantioselective Diels-Alder reactions were conducted successfully using chiral magnesium complexes prepared from magnesium iodide and chiral hydroxysulfoxides derived from ( R)- and ( S)-methyl 1-naphthyl sulfoxide. Convenient methods for the preparation of these chiral sulfoxides have also been developed. Hydroxysulfoxide 6 (and its enantiomer 10) showed the highest enantioselectivity.

Enantioselective Diels-Alder Reaction Using Chiral Lewis Acid Prepared from Grignard Reagent and a Chiral 2-(2-p-Toluenesulfonylamino)phenyl-4-phenyloxazoline

Enantioselective Diels-Alder reaction was conducted successfully using a chiral magnesium complex prepared from Grignard reagent and a chiral 2-(2-p-toluenesulfonylamino)phenyl-4-phenyloxazoline derived from easily available D-phenylglycine as a chiral auxiliary. The endo-isomer was exclusively obtained with 91%ee from the reaction of 3-crotonoyl-1,3-oxazolidin-2-one and cyclopentadiene.

Enantioselective Diels-Alder reaction using chiral Lewis acid prepared from grignard reagent and a chiral 2-(2- p-toluenesulfonylamino)phenyl-4-phenyloxazoline

Enantioselective Diels-Alder reaction was conducted successfully using a chiral magnesium complex prepared from Grignard reagent and a chiral 2-(2- p-toluenesulfonylamino)phenyl-4-phenyloxazoline derived from easily available D-phenylglycine as a chiral auxiliary. The endo-isomer was exclusively obtained with 91%ee from the reaction of 3-crotonoyl-1,3-oxazolidin-2-one and cyclopentadiene.

Preparation and study of chiral magnesium porphyrin-amino acid complexes

Mixtures of magnesium protoporphyrin or magnesium mesoporphyrin with a variety of chiral amino acids (L-histidine, D- and L-proline, L-serine and L-threonine) produce prominent induced Cotton effects in the UV-visible region. By contrast magnesium deuteroporphyrin mixtures exhibit no optical rotatory dispersion (ORD)/circular dichroism (CD) spectra. It is proposed that the species producing the Cotton effects are six-coordinate species of the type Mg (porphyrin) (amino acid)2. For L-histidine and L-threonine CD spectra have shown that complexes of the opposite chirality can be obtained for different samples of magnesium protoporphyrin. For D- and L-proline such a change in sign of spectra was not found for the same magnesium porphyrin samples. Reasons for these observations are presented together with proposals regarding structural details of the six-coordinate complexes. It is also suggested that racemic samples of such amino acid-magnesium porphyrin mixtures could yield optical resolution of products on irradiation with circularly polarised light. Details of a study of this type are presented.

Asymmetric synthesis with carbohydrates. Part 2. Asymmetric grignard addition reactions conditioned by chiral magnesium alkoxides

Enantioselective Grignard addition reactions are described in which magnesium alkoxides derived from 1,2:5,6-di-O-isopropylidene-α-D-allofuranose and 1,6-dideoxy-3,4-O-isopropylidene-2,5-di-C-methyl-L-threo-hexitol are used to provide chiral complexation of the Grignard reagent. A stereochemical interpretation of these and other results is presented.