CREATION OF TRIDENTATE TRANS-CHELATING CHIRAL LIGAND BASED ON A NEW MOLECULAR STRUCTURE DESIGN

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Establishment of a useful method of chirality control in catalyzed asymmetric reactions is one of the central subjects in the field of synthetic organic chemistry in 21st century. In the present research, we have designed and synthesized a new trans-chelating tridentate chiral ligand which has a dibenzofuran skeleton having two oxazoline substituents at 4- and 6-positions. From the study of a wide variety of asymmetric reactions catalyzed by the transition metal complexes of this new ligand, 4,6-dibenzofurandiyl-2,2-bis(4-phenyloxazoline) designated hereafter as DBFOXIPh, new findings as well as useful informations have been obtained as shown below :1. DBFOX/Ph Ligand forms stable complexes with the transition metal ions such as Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(lI) perchlorate hexahydrates. Some complexes can be isolated and show high catalytic activity as Lewis acids.2. The aqua nickel(II) complex of DBFOX/Ph ligand can be stored for months in air under moisture conditions w … More ithout loss of catalytic activity.3. The nickel complex catalyzes the Diels-Alder reactions between cyclopentadiene and 3-acryloyl-2-oxazotidinone to show the absolute endo selectivity and enantioselectivity.4. Aqua complexes show even higher levels of enantioselectivity and catalytic activity than the anhydrous complexes.5. The nickel and zinc complexes show extremely effective chiral amplification in the catalyzed Diels-Alder reactions.6. Two mechanisms have been proposed : (1) the precipitation of inert mesa 2 : 1 complex in the preparation stage of catalyst, (2) the heterochiral aggregation of 1 : 1 complexes is more stable than the homochiral aggregation.7. The aggreagtion of 1 : 1 complexes is based on the hydrogen bonding working between the water ligand and the perchiorate ions..8. The nickel complex shows sufficiently high catalytic activity in the reaction medium containing coordinating additives such as water, alcohols, carboxylic acids, and amines.9. The nickel and zinc complexes work as excellent catalysts in the nitrone cycloadditions using 3-crotonoyl-2-oxazolidinone to show the absolute endo selectivity and enantioselectivity.10. The zinc complex works as excellent catalyst in the diazo cycloadditions to 3-crotonoyl-2-oxazolidinone to show the absolute enantioselectivity, On the other hand, the magnesium complex is the best in the reaction of 3-crotonoyl-4,4-dimethyl-2-oxazolidinone where the mode of enantioselectivity is completely reversed. This result offers an interesting example of "ligand - auxiliary coorperative stereo control".11. The nickel complex catalyzes the conjugate addition of thiols to 3-crotonoyl-2-oxazolidinone to produce the conjugate adducts in high enantioselectivities. Less