STEREOCHEMISTRY OF A CARBON-CARBON BOND-FORMING PROCESS

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The thermolysis of alpha-silylalkyl carboxylates results in the 1,2- migration of an unactivated alkyl group from silicon to carbon accompanied by a reverse migration of carboxylate. This extremely efficient rearrangement occurs at temperatures between 100 and 250 degrees C. The stereospecificity of this reaction will be investigated with the goal of developing a synthetically useful process for the formation of carbon-carbon bonds. Such processes are crucial to the preparation of biologically active materials. The reaction possesses several advantages over other dipolar or boron-mediated methods for the formation of carbon-carbon bonds: 1) It occurs under extremely mild conditions, without strong bases or acids; 2) The silicon atom provides a convenient, disposable handle to direct the formation of chirality in the alkyl fragments; 3) Since neither carbon fragment must undergo conversion to a highly reactive species (such as a carbanion), both centers should remain chiral (through either inversion or retention of configuration), thus allowing the stereospecific joining of two carbon atoms without the need for a chiral auxiliary; 4) The large number of ways for the formation of carbon-silicon bonds will permit the application of this methodology to the preparation of a variety of systems. Absolute chirality will be created at the migratory and terminal carbon atoms as well as at silicon. Chirality at the terminal, oxygen-bearing, carbon will be introduced by the reduction of acyl silanes with chiral borolane reagents. The resultant chiral silylcarbinols will also be evaluated as synthetic precursors to currently inaccessible chiral alcohols via both intra- and intermolecular processes. Chirality at the migratory carbon atom will be introduced by the reaction of silyl anions with the tosylates of available chiral alcohols. Silanes which are chiral at silicon will be prepared through stereospecific transformations of (+)-alpha-naphthylmethylphenylsilane.