Ein Beitrag zum Mechanismus der singulett-angeregten Photo-Isomerisierung des Homofulven-Systems / On the Mechanism of the Singulet Excited Photo-Isomerization of the Homofulvene System

Abstract

Syntheses of the four at the cyclopropane part alkyl-substituted homofulvenes 6-endo-Ethyl-1,2,3,5-tetramethyl-4-methylenebicyclo[3.1.0]hex-2-ene (endo-1a), 6-exo-Ethyl-1,2,3,5-tetramethyl-4-methylenebicyclo[3.1.0]hex-2-ene (exo-1a), 6-ercdo-Isopropyl-1,2,3,5-tetramethyl- 4-methylenebicyclo[3.1.0]hex-2-ene (endo-1b) and 6-exo-Isopropyl-1,2,3,5-tetramethyl-4-methylenebicyclo[ 3.1.0]hex-2-ene (exo-1b) are reported. Following singulet excitation endo-1a, endo-1b and exo-1b underwent photo-isomerization to 6-Ethyl-1,2,3,4-tetramethyl-5-methylenecyclohexa- 1,3-diene (2a) and 6-Isopropyl-1,2,3,4-tetramethyl-5-methylenecyclohexa-1,3-diene (2b) resp. It is demonstrated, that C-6 - the top of the cyclopropane ring in 1 - is transferred to C-6 - adjacent to the exo-methylene substituent - in the 5-methylenecyclohexa-1,3-diene system 2. A mechanism is suggested.