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The focus of my graduate research in the Krische group has been the development of catalytic carbon-carbon bond forming reactions with an emphasis on controlling diastereo- and enatio-selectivity in transfer hydrogenative couplings. The broad goal of our research program has been the development and implementation of efficient green methods for carbonyl addition employing [pi]-unsaturates as surrogates to preformed organometallic reagents, thus enabling byproduct free variants of traditional carbanion chemistry. This dissertation shows the new reactions that I have developed toward this goal. These reactions includes new metal catalyzed approaches for carbonyl crotylation, aminoallylation, and vinylogous reformatsky aldol reactions. / text

Carbon-Carbon bond forming reactions are very important in organic synthesis. Preparation of most of the leading drugs on the market involves at least one carbon-carbon bond forming transformation. However, use of preformed oganometallics for this purpose is neither atom economical nor cost effective. Thus, development of atom economical and environmentally benign carbon-carbon bond forming methods is highly desirable. Catalytic hydrogenation is one of the most widely used transformations in the pharmaceutical and chemical industry. However, for several years the catalytic hydrogenation was limited to the carbon-carbon bond forming processes such as alkene hydroformylation and the Fischer-Tropsch reactions. In 2004 Krische group demonstrated a novel reductive aldol cyclization under rhodium catalyzed hydrogenation conditions. Following this, a variety of reductive carbon-carbon bond forming reactions were developed under hydrogenation conditions. The first chapter of this dissertation summarizes the reductive couplings of π-unsaturates to imines. N-heterocyclic compounds are very valuble in pharmaceutical and agrochemical industries. In the second chapter a variety of hydrogen mediated reductive couplings to aromatic N-heterocycles have been described. Transfer hydrogenation represents another important class of reactions in organic chemistry. This process employs hydrogen sources other than gaseous dihydrogen, such as isopropanol. Very recently, the Krische group reported a number of novel C-C coupling reactions using the concept of transfer hydrogenation. Thus, in chapter 3 a very elegant ruthenium catalyzed allylation reaction has been described. Finally, chapter 4 focuses on the reactivity of zinc enolates toward less reactive electrophiles such as allylic carbonates in the absence of any transition metal catalyst. During this process a direct allylic substitution of allylic carbonates with diorganozinc reagents has been discovered. These two transformations are conceptually very interesting. / text

Although α-keto carbocations have been demonstrated to be viable intermediates in solvolysis reactions, their applications in synthesis are scarce. These species can be considered to be equivalent to “reversed polarity” enolates and, as such, could be useful for the asymmetric formation of carbon-carbon and carbon-heteroatom bonds. In principle, facial selectivity in additions to α-keto carbocations may be induced using easily removed ester, amide, or imide chiral auxiliaries. Efforts to achieve such diastereoselective SN1 reactions of α-keto carbocations are described herein.

Although α-keto carbocations have been demonstrated to be viable intermediates in solvolysis reactions, their applications in synthesis are scarce. These species can be considered to be equivalent to “reversed polarity” enolates and, as such, could be useful for the asymmetric formation of carbon-carbon and carbon-heteroatom bonds. In principle, facial selectivity in additions to α-keto carbocations may be induced using easily removed ester, amide, or imide chiral auxiliaries. Efforts to achieve such diastereoselective SN1 reactions of α-keto carbocations are described herein.