Spin centre shift in photochemically generated biradicals - A new ring closure approach

The irradiation of alkyl-aryl-ketones bearing a leaving group adjacent to t he carbonyl C-atom affords 1-hydroxy-1, n-biradicals, which undergo within its lifetime a very rapid elimination of acid giving 1-oxo-2, n-biradicals. We have called this process spin centre shift due to the shortening of the original biradical. In the current publication we present a first syntheti c application of this approach. Starting with alpha -sulfonyloxy-alkyl-aryl ketones a short and straightforward method for preparation of highly functi onalized cyclopropanes was developed. The method is tolerant towards many f unctional groups and it even allows the synthesis of highly strained hydroc arbons such as bicyclo[2.1.0] pentanes.