Photolytic cleavage ring contraction

The photolytic cleavage of cyclic ketones 14 leads to formation of a diradical species, that can undergo analogously the various reactions outlined above. The decarbonylation followed by intramolecular recombination yields a ring-contracted cycloalkane 15 ... 

Oxidation of solutions of benzodiazepines in benzene or acetic acid with a high-pressure mercury arc in oxygen also causes oxidative ring contraction to give quinoxalines.49 Since hydrolytic cleavage is ruled out in this case a photolytic norcaradiene-type rearrangement of the intermediate ketone to a quinoxaline was suggested (Scheme 5). 

Photolytic or thermolytic cleavage of the N-0 bond of tetrahydro-1,2-oxazine-3,6-diones (407), followed by decarboxylation, gives intermediate 1,4-diradicals (408) which close to form 3-lactams (409), albeit in poor yields. Diradical intermediates analogous to (408) may be formed in the biosynthesis of isopenicillin N from trlpeptide precursors. In a similar vein, Easton has published full details of the synthesis of 3-lactams by ring contraction of isothiazolidinones, a reaction which may also be relevant to... 

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