PUB - Publikationen an der Universität Bielefeld

The intramolecular cycloaddition reactions of the tetraene ethers 10 and 17 and the triene ether 28 were investigated. Acetone-sensitized excitation of 10 led to three intramolecular [2 + 2] cycloadducts 11-13. However, CuOTf-catalyzed photolysis of 10 gave two rearranged products 15 and 16 via copper(I)-catalyzed, photoinduced [1, 3] and [3, 3] rearrangement reactions of the divinylcyclobutane intermediates 11-13. The Cope product 14 is the precursor of the tetracyclic product 16 in a photocatalytic process. All photochemical products contain cis-fused rings. By analogy with the photochemical reactions of 10, acetone-sensitized photolysis of the tetraene ether 17 afforded four intramolecular [2 + 2] cycloadducts 18-21. The dipropenycyclobutanes 18-21 were formed as intermediates under CuOTf-catalyzed irradiation of 17 as well. However, longer irradiation times led to four rearranged products 22-25. Two cyclooctadiene intermediates 26 and 27 are the precursors of the tetracyclic products 24 and 25. Acetone-sensitized or CuOTf-catalyzed photolysis of the triene ether 28 gave two vinylcyclobutanes 29 and 30, but no copper(I)-catalyzed ring expansion reactions were found. Thermolysis of 10 in toluene at 150-degrees-C produced a mixture of four isomeric vinylcyclohexenes 31, 32, 15, and 33, whereas the CuOTf-catalyzed intramolecular Diels-Alder reaction in THF at 80-degrees-C showed an improved selectivity, the trans-fused hexahydroisobenzofuran derivative 31 being the main product. Thermolysis of 17 in toluene at 150-degrees-C gave two cyclohexene derivatives 22 and 34. Thermolysis of 28 at 150-degrees-C resulted in formation of two bicyclic cyclohexenes 35 and 36. Also, the thermal rearrangement reactions of the divinylcyclobutanes 11-13 and the dipropenylcyclobutanes 18-21 were studied. Initial experiments concerning the activity of copper(II) triflate as catalyst for the described intramolecular cycloaddition reactions were carried out.