2581-87-5Relevant articles and documents
2,2′-Bis-azonia-cope rearrangements of 2,3-homo-6H-1,4-diazepinium dications
Quast, Helmut,Seidenspinner, Hubert-Matthias,Stawitz, Josef Walter
supporting information, p. 4852 - 4862 (2013/08/23)
The condensation of cis-1,2-cyclopropanediamines with 1,3-dicarbonyl compounds and 1,5-diazapentadienium salts afforded 2,3-homo-1H-1,4-diazepinium salts, which were protonated by very strong acids to yield 2,3-homo-6H-1,4- diazepinium dications. As measures of basicity, the mole fractions of water in trifluoromethanesulfonic acid at half-protonation were determined for 2,3-homo- and 2,3-dihydro-1H-1,4-diazepinium salts. 2,3-Homo-6H-1,4-diazepinium dications underwent 2,2′-bis-azonia-Cope rearrangements, as can be inferred from the product structures, or H/D exchange involving the methylene group of the cyclopropane rings. Apparently, in the Cope rearrangement, this group is interchanged with the methylene group in the seven-membered ring (C-6), which is susceptible to H/D exchange in strong deuteriated acids. Rapid, degenerate, as well as very slow, strongly biased Cope rearrangements have been uncovered in this way. 1H NMR spectra, recorded at elevated temperatures for a solution of the parent dication in trifluoromethanesulfonic acid, reveal broadening of the interchanging 2-H, 3-H and 5-H, 7-H signals and eventually the onset of their coalescence. Surprisingly, the estimated free enthalpy of activation is higher (ΔG?110 °C ≈ 73 ± 2 kJ/mol) than that of 3,4-homotropilidene (ΔG ?110°C = 61 kJ/mol), not lower, as would be expected on the basis of the well-known charge-acceleration of Cope rearrangements. Copyright
