Über En-synthesen mit Singulett-Sauerstoff [1] II. Die Farbstoff-sensibilisierte Photooxygenierung von (—)-Thujopsen und die Stereochemie der dargestellten Thujopsanole

The dye-sensitized photooxygenation of (–)-thujopsene (1) leads to two allyl hydroperoxides 16 and 17 (ratio 2:1). From the structure of the corresponding alcohols 2 and 3 it is possible to demostrate the complete stereospecificity of the addition of 1Δg-oxygen to the acceptor system. In this way it is shown that 1 exists in only one conformation in solution. The production of the rearranged product 23 can be explained by Hock fission from the allyl hydroperoxides 16 or 17 following the Criegee mechanism. Under the epoxidation conditions 1 is converted mainly to the two new odorous substances (–)-3-thujopsanone (4) and (–)-3-isothujopsanone (5). A series of sesquiterpenes with the thujopsane skeleton is also described, all of which have been intercorrelated.