Numerous medicinally important compounds are chiral. However, often only one enantiomer of a chiral drug evokes the desired physiological response. Syntheses which provide racemic drugs are wasteful and potentially dangerous. Also, compounds which are chiral by virtue of hydrogen-deuterium substitution, or hydrogen-deuterium-tritium substitution (chrial methyl group), have played important roles in the elucidation of biochemical mechanisms. There is a distinct need for better general methods for the asymmetric synthesis of medicinal agents and isotopically labeled compounds. We propose to investigate the utility of chiral pseudotetrahedral organorhenium complexes (Pi5-C5H5)Re(NO)(PPh3)(X) as chiral auxiliaries in asymmetric organic synthesis. These compounds are easy to synthesize and obtain optically pure. Many reactions have been discovered in which the rhenium-centered chirality is stereospecifically transferred to a new ligand-based chiral center. Through labeling experiments, X-ray crystallography, and MO calculations, we seek to define the mechanistic basis for this asymmetric induction. Among many objectives, we intend to (a) develop new routes to optically active (Pi5-C5H5)Re(NO)(PPh3)(X) complexes; (b) effect 1,2-, 1,3-, 1,4-, and 1,5-asymmetric induction via Diels-Alder reactions of rhenium dienyl and related complexes; (c) effect 1,2-, 1,3-, and 1,4-asymmetric induction via reactions of alkyl ligand carbanions that are Alpha-, Beta-, and Gamma- to the rhenium; (d) develop diastereoselective syntheses and reactions of aldehyde, alkene, and ketone complexes; (e) develop metal-carbon bond cleavage reactions that are stereospecific at carbon; (f) develop enantioselective syntheses of compounds with chiral methyl groups; and (g) develop applications of chiral rhenium complexes in catalysis. From this program of fundamental research, improved syntheses of several types of medicinally important compounds will be realized.
