ABSTRACT
The photocycloaddition of (cyclic) a,b-unsaturated ketones to alkenes affording cyclobutanes as products comprises the four reaction types shown in Sch. 1, i.e., (a) intermolecular enoneþ alkene cycloaddition; (b) cycloisomerization of alkenylsubstituted enones; (c) photocyclodimerization of enones, one ground state enone molecule acting as ‘‘alkene’’; and (d) cycloisomerization of bis-enones.
