Electronic Excited States of the Cyclic 1,4-Diaza-1,3-diene (Cyclic α-Diimine) System. Photochemical Reactions of 2H-Isoimidazole, 5,6-Dihydropyrazine, and 1,4-Diazepine Derivatives

Abstract

The five-, six-, and seven-membered cyclic 1,4-diaza-l,3-dienes have been irradiated under a variety of conditions. The six-membered ring (dihydropyrazine) opens in a 6ne valence isomerization reaction. The resulting enediimine is stable at low temperatures and has been characterized (i.r.). Irradiation of 2,3,5,5-tetramethyl-5,6-dihydropyrazine (lb) results in formation of the enediimine 26 which reacts further to give the rearranged monomer 12 and/or dimers 13 depending upon the temperature. The fiveand seven-membered systems are stable to irradiation in inert solvents. However, irradiation of 2,2-dimethyl-4,5-diphenylisoimidazole (10h) in isopropyl alcohol gives the dihydroderivative 19 and in tetramethylethylene the one-to-one adduct 25.The U.V. spectrum of the six-membered ring (5,6-dihydropyrazine) is very different from that of the five-and seven-membered rings. The long wavelength maximum (ca. 350 nm) of the six-membered ring is attributed to a transition directly into an excited state common to the enediimine 2 (i.e., the excited state has a node between C-5 and -6 of the dihydropyrazine).

Synthesis and DNA Strand Breakage Activity of Some 1,4-Diazepines.

“…To obtain further information on pyrazine analogues, we investigated the reaction of 1,3-propanediamine (PD) with a-dicarbonyl compounds. In this paper, we describe the synthesis of 6,7-dihydro-5H-1,4-diazepines (2b-d) 9,10) and a related 1,4-diazepine-type compound 2Јe 8) in a one-pot reaction and evaluate their DNA breakage activities.…”

Ag+-catalyzed rearrangements. XIV. Influence of structural features of the course of bicyclo[1.1.0]butane rearrangements catalyzed by silver(I) ion

“…However, the involvement of 6 cannot be summarily dismissed, since its independent generation from diazo compound 5 was found to lead chiefly (81%) to 2. In particular, the preponderance of vinyl migration in 6 conforms to the fact that vinyl groups exhibit a greater relative migratory aptitude to cationic centers than alkyl substituents. 9 Exposure of 1,3-dimethylbicyclobutane (7) to the same conditions resulted in relatively slow (qualitative (8) H. K. Hall, Jr., C. D. Smith, E. P. Blanchard, Jr., S. C. Cherkofsky, and J. B. Sieja, J. Amer.…”

The Photochemistry of a Dihydropyridazine

“…It has been suggested by Arnold et al (14) in connection with the u.v. absorption spectrum of the dihydropyrazines that the excited state of the dienes actually lies on the same surface as the spectroscopic transition from the triene: that is.…”