NEW LIGANDS FOR ASYMMETRIC SYNTHESIS AND CATALYSIS

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A plan is presented to develop a class of chiral Iigands for use in transition metal and Lewis acid mediated asymmetric reactions of value in organic synthesis. Specifically, these are the ligands 13, 14, 86, 87,101 - 106, 111 and 116. All of these ligands are either 2,2'-binaphthyls or 3,3'-biphenanthryl derivatives. None of these ligands have been made before, and in the preliminary results section methods are described which have been developed for the synthesis of 13 and 14. Proposed syntheses of the other ligands are presented. Two general methods are presented for the preparation of these ligands. The oxidative coupling method has been shown to be viable for 13 and 14 and some preliminary evidence is presented to suggest that approaches involving the benzannulation reaction of chromium carbene complexes may have potential. The greatest aspect of this potential is that carbene complexes may provide a route for the asymmetric synthesis of these ligands which would obviate the normally tedious resolution procedures that are required. In a preliminary evaluation of these ligands as chiral controllers it was found that a chloroaluminum complex of ligand 14 gives high asymmetric induction in the Diels-Alder reaction of methacrolein and cyclopentadiene (98 % ee) and in addition will produce 200 turnovers (0.5 mole % catalyst) in 4 h at -78 degrees C. Possible sources of the particular facial selectivity observed for the catalysts derived from these ligands are discussed. Several experiments involving the construction of new ligands are described which are designed to probe the source of the asymmetric induction. In addition to the Diels-AIder reaction, it is proposed that these ligands be evaluated with regard to their utility in asymmetric heteroatom Diels-Alder reactions, aldol reactions, Claisen rearrangements, carbonyl additions, reductive cyclizations, and carbometallation reactions. In addition it is noted that these ligands bear some structural relationship to gossypol, a naturally occurring 2,2'-binaphthol which occurs in cotton seeds and other natural sources. Given the known biological properties of gossypol, it is suggested that some of these ligands and the intermediates in their syntheses be tested for antiviral and anticancer activity.