Photochemistry of Nitrogen Heterocycles

Three ylidenemalononitrile enamines were designed as fast and selective primary amine sensors. These sensors were used as both colorimetric and fluorometric sensors for primary amines in solution. Two of the enamines were coated onto various media and were used to detect primary amine vapors. The enamine derived from acenaphthalene was used as a colorimetric sensor when coated on media. The enamine derived from 2-phenylacetophenone showed a stronger fluorescent turn-on when coated on media and was used as a fluorescent sensor when coated on media. Each enamine worked to detect primary amines in complex mixtures without sample preparation. Each sensor was generated in short reaction sequences that ranged from three to four steps that utilized mild reaction conditions. In addition, each enamine sensor was synthesized from inexpensive and commercially available starting material. Pyridazine N-oxides were used as photochemical intermediates for the synthesis of 3,5-disubstituted pyrazoles. These photochemical precursors were synthesized regioselectively following the oxidation of the commercially available dichloropyridazine. In order to obtain the regioselectivity a Suzuki coupling reaction followed by a nucleophilic aromatic substitution (SNAr) was completed on the molecule using various boronic acids and pyrrolidine. Followed by photochemical ring opening the disubstituted pyridazine N-oxide generated a diazo carbonyl intermediate that could then have cyclized into either a furan or pyrazole. By partitioning between the two mechanisms we were able to selectively synthesize the pyrazole with little to no furan by product.