A New Photochemical Route to Cyclopropanes and Bicyclo[n,1,0]alkanes

Up to now only few examples of cyclopropane syntheses by NORRISH-YANG-reaction are known. In most of these cases an initial PET to the excited carbonyl group was proven or seems very likely basing on the modern state of knowledge. [1,2] In the following we would like to present a new method to prepare highly functionalized cyclopropanes. It is well known by the chemistry of monoradicals that radical centres are excellent neighbouring groups for the nucleophilic substitution. [3,4] The -hydroxy radicals 1 occupy a special position. If X is a suited leaving group the elimination of the acid HX occurs without formation of any ionic intermediates and with rate constants k > 109 s-1. [5,6] It is noteworthy, in the formed enolate radical 2 the highest spin density is now mainly localized at the adjacent carbon atom.