Photoswitchable enediynes: use of cyclopropenone as photocleavable masking group for the enediyne triple bond

Cyclopropenone 1, 2,3-benzobicyclo[8.1.0]undec-1(10)-en-4-yn-11-one, is a thermally stable compound showing no signs of decomposition after heating at 84 °C for 7 d, UV irradiation of which results in an efficient ((phi)300= 0.45) and quantitative formation of benzannelated enediyne 2, which undergoes Bergman cyclization at the above temperature.