The acid-catalyzed self-condensation reaction of b-diketones in the presence of 2,2,2-trifluorodiazoethane
A novel acid-catalyzed self-condensation reaction of 6-diketones in the presence of 2,2,2-trifluorodiazoethane (TFD) has been discovered. This reaction is of interest because not many methods are available for the preparation of cyclized products (e.g., aromatic natural products) from 6-dicarbonyl units. Acid-catalyzed reactions of 1-phenyl-1,3-butanedione and several substituted derivatives of 1- phenyl-1,3-butanedione with TFD afforded two groups of substituted biphenyl compounds. One of these groups could be an important synthon for the preparation of larger polycyclic aromatic compounds. Several cyclized products have also been obtained from the reaction of 2, 4-pentanedione with TFD. Two potential mechanisms have been suggested to describe this cyclization process. Mechanistic studies utilizing dienophiles suggest that the previously described cyclized products have originated from Michael addition reactions. Several NMR techniques have been utilized to characterize the reaction products which were obtained in this study. These techniques include ¹³C labeling, the ¹³C NMR INADEQUATE pulse experiment, and applications of lanthanide shift reagents. The results that were obtained from the lanthanide shift reagent studies illustrate that certain oxygen atoms can be converted to 2, 2, 2-trifluoroethyl ethers to prevent complexation with lanthanide shift reagents. This methodology was successfully utilized to simplify the interpretation of lanthanide shift reagent results that were obtained from polyfunctional molecules. The reactions of several additional β-diketones have also been studied to better understand the cyclization process.