New Strategies for the Synthesis of Carbocyclic and Heterocyclic Compounds

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The Organic Synthesis Program is funding the continuation of the research program of Dr. Rick L. Danheiser. Dr. Danheiser will continue his fruitful development of new methods to synthesize carbocyclic and heterocyclic compounds containing five-membered rings. This will provide the new tools required by the increasingly complex requirements of industry and agriculture. One important aim of the project is the continued development of the recently discovered general ı3+2! annulation strategy. In this process an allenylsilane functions as a three-carbon annulation unit combining with an electrophilic pi bond to form a new five-membered ring. The extension of this strategy to the synthesis of several important classes of five-membered ring compounds will be investigated. Specific targets of interest include cyclopentanone derivatives and heterocyclic systems such as pyrroles and carbapenems. Research will also be carried out aimed at the development of a general synthesis of substituted azulenes. The azulenes constitute the best known class of polycyclic nonbenzenoid aromatic compounds, and recently the novel electronic properties and biological activity of certain natural and semi-synthetic azulenes have led to commercially important applications of these compounds in fields such as medicine and electrophotography. However, progress in these areas has been hindered by the availability of very few general methods for the synthesis of azulenes, particularly substituted systems. The development of a general ı3+2! annulation route to substituted azulenes will provide access to compounds with potential applications as drugs, liquid crystal elements, and novel electronic materials. Another important objective of the project is the development of new cyclization methods based on unusually facile pericyclic and anionic ring closure reactions of allenes. Preliminary experiments have been carried out that indicate that certain allene derivatives undergo efficient cyclization under remarkably mild conditions. A principal aim of the project will be the application of this process in a new synthesis of substituted indoles. The indole nucleus is the central structural feature in a large array of natural products including plant growth regulators and clinically important pharmaceuticals. Relatively few general methods for the construction of substituted indoles exist, and the new methodology to be investigated will provide improved access to a variety of important indole derivatives.