Cycloaddition and Rearrangement Reactions of Unsaturated Carbonyl Compounds

3 Cycloaddition and Rearrangement Reactions of Unsaturated Carbonyl Compounds 

Cyclopentenone 56 having a propyl-like substituent undergoes photosensitized intramolecular hydrogen abstraction to give rearrangement product 57 and cycloadduct 58 [30]. 

The dimerization occurs via the formation of a 1,4-diradical intermediate followed by addition with a ground-state molecule. 

The stereochemistry of ring junction was studied in the cycloaddilion of cyclohexenone with isobutene. The trans-hng closure is the preferred cyclization process because of minimum steric repulsion [34], 

4-Dialkylcyclohexenone 60 undergoes photo-induced lumiketone rearrangement to form cyclopropane derivative 61 [35]. 

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