Honors Theses


Jeremy Erb, Ph.D.



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Honors Thesis


The use of benzotetramisole (BTM) as a catalyst is a promising strategy for enantioselective organophosphorus synthesis since the reaction has been previously reported by Numan and Brichacek and has been tested in Dr. Erb’s research laboratory. However, the yields are only moderate (46-58%) and the enantiomeric excess (ee) of the purified product are poor, with 62% being the highest reported ee. Preliminary computational data performed in the Erb lab has revealed that the cause of the lower ee (and possibly yield) could be the ability of the intermediate to adopt different conformations that are similar in energy and would therefore give a mixture of chirality in the product. The addition of a metal ion could result in the formation of a cyclic intermediate, providing a firm anchor that prevents rotation of the phosphorus-nitrogen bond, forming two possible intermediates and restricting conformational changes. Locking the rotation of the intermediate prevents the relief of steric strain between groups on the substrate and the organocatalyst in one intermediate, thus making it much higher in energy, less stable, and less likely to form. The other intermediate would also be locked in place in a similar way but has lower steric strain and thus would be more favorable. It may even be possible that the higher energy intermediate can isomerize to form the lower energy intermediate. Following this, bimolecular substitution by a nucleophile, such as an alcohol, would release of the catalyst and provide the product in improved enantioselectivity or yield. Several metals were tested to examine their effect on yield and enantioselectivity. Our results indicate that use of a bifunctional catalytic system with BTM and metal Lewis acids yields similar results to literature values obtained by use of BTM alone.

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Undergraduate research