Strahlenchemische Cycloadditionen mit Äthylen und Acetylen (Produktbildung und Lösungsmittelwahl) / Radiation Chemical Cycloaddition Reactions with Ethylene and Acetylene

The (2+2) cycloadditions of maleic acid anhydride (MSA) and 1,3-cyclohexadiene (CHD) to ethylene and acetylene were initiated with gamma-rays in different solvents. The four-membered ring products were formed with high selectivity and surprisingly high energy yields in solvents with triplett energies smaller than ethylene and acetylene but higher than MSA and CHD resp. In benzonitrile as a solvent MSA reacts with ethylene to give cyclobutane-1,2-dicarboxylic acid anhydride (1) (G = 0.04) and with acetylene to give cyclobut-3-ene-1,2-dicarboxylic acid anhydride (2) (G = 3.7). The cyclobutene derivative (2) is formed in ≥ 80% yield and the bicyclopropyl derivative (8), which is the main product in the photochemical reaction, with a yield of ≤ 20%. 1,3-Cyclohexadiene was also added to ethylene to give bicyclo(4,2,0)oct-2-ene (G = 0.4) and bicyclo(2,2,2)oct-2-ene (G = 0.1) under gamma irradiation in methylnaphthalene as a solvent. Under similar conditions addition to acetylene gave bicyclo(4,2,0)octa-2,7-diene (G = 0.04) and bicyclo(2,2,2)octa-2,5-diene (G = 0.3), respectively.