The newly synthesized 2-acylcyclohex-2-enones 1 photocycloadd selectively t
o the C-C triple bond of 2-methylbut-1-en-3-yne giving diacylcyclobutene de
rivatives 4 and 5, and they react with 2,3-dimethylbut-2-ene in an overall
[4+2]-photocycloaddition to afford benzopyranones 7.