Preparation of Pyrroles from Ketoximes and Acetylenes

Abstract

This chapter discusses the preparation of pyrroles from ketoximes and acetylenes. The chemistry of pyrroles also includes complex pyrrole systems, porphirin, and phthalocyanine structures such as haemin, chlorophill, hemoglobin, bile pigments, cytochromes, and vitamin B12. Ketoximes react with acetylenes in a strong base/DMS0 system to form NH- and N-vinylpyrroles. The reaction of ketoximes with acetylene has become popular as a reliable preparative tool for wide application in the chemistry of pyrroles. The reaction of heterocyclization with acetylene to form NH- and Nvinylpyrroles involves all ketones having at least one methylene or methyl group in the a-position to the oxime function and no substituents susceptible to the action of bases. Extention of the reaction of ketoximes with acetylene to oximes of hydroxyalkyl ketones can lead to the synthesis of inaccessible, functionally substituted pyrroles and N-vinyl derivatives. The ketoximes containing only tertiary or aromatic radicals in any combination do not form pyrroles when reacting with acetylene in the presence of superbases. The chapter discusses influence of the acetylene structure and the use of acetylene equivalents. Systematic research on the synthesis of pyrroles and especially of N-vinylpyrroles from ketoximes and acetylene is in progress. This is expected to lead to not only further extension of the preparative possibilities of the reaction, but also to discovery of new versions and analogs. The increased access to N-vinylpyrroles stimulates more and more synthetic and theoretical investigations in this field as well as work dealing with polymerization and practical application of these compounds.