Rearrangement of the intermediate 1,4-biradicals in photocycloaddition of cyclohex-2-enones to alkenes

Two unusual examples of enone/alkene photocycloaddition involving a rearrangement of the intermediate 1,4-biradical are presented. The first reaction proceedsvia the addition of one of the radical centers to a carbonyl C aton and subsequent bond cleavage,i.e., with rearrangement to a 1,3-biradical, while the second reaction involves abstraction of an H atom by one of the radical centers. The material was partly presented as an invited lecture by Paul Margaretha at the Sixth International Conference on the Chemistry of Carbenes and Related Intermediates (St. Petersburg, May 28–30, 1998). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 514–516, March, 1999.