Synthesis of Heterocyclic Compounds Through Oxazolium Salt and Azomethine Ylide Cycloaddition

Heterocyclic compounds such as pyrroles and pyridines are notably useful for medicinal purposes. Heterocyclic pyrrole rings are present in naturally-occurring cofactors, such as in hemoglobin and chlorophyll, and are present in drugs used today to treat cancer and cardiovascular disease. There are a variety of methods for synthesizing such heterocyclic molecules, and the method of 1,3-dipolar cycloaddition may be particularly effective in producing pyrrolic compounds. This research focuses on the oxazolium salt/4-oxazoline/azomethine ylide method for assembling the heterocycle. The oxazolium salt is opened by a nucleophile and converted to an azomethine ylide, which undergoes a 3+2 cycloaddition with an appropriate dipolarophile and produces a new five-membered ring. This method shows promise for generating sensitive functional groups in the molecule being cyclized. Our efforts are directed towards varying the size and position of the tethered dipolarophile, specifically examining C2 and N3 substituted oxazoles in order to take advantage of the opportunities provided by the oxazolium salt/4-oxazoline/azomethine ylide process