Cyclobutanone synthesis, photochem

Synthesis of a cyclic 1,3- dicarbonyl compound from an acyclic 1,2-dicarbonyl compound may be achieved in two steps by a photochemical cyclisation followed by a cationic rearrangement in which the cyclobutanone acyl group migrates preferentially [equation (40)].141... 

The synthesis of cyclobutanones can in some cases be accomplished more efficiently by addition of a ketene-iminium salt or a chromium carbene to an alkene. For example, under photochemical conditions, the chromium carbene 174 gave the cyclobutanone 175 as a single diastereomer (3.118). The product 175 was converted to the antifungal antibiotic (-l-)-cerulenin by way of the lactone 176. 

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