Substituent effects on the photohydration of 1-aryl-5,5-dimethyl-1,3-hexadiynes

The photohydration of 1-aryl-5,5-dimethyl-1,3-hexadiynes in aqueous sulfuric acid (10% H2SO4) yields two types of alkynyl (type A and type B) and allenyl ketones (type C and type D) through both S-1 and T-1 excited states when diynes are substituted by other than a nitro group. The electron-withdrawing substituents favor C-1 protonation giving type C allenyl ketones, while the electron-donating group yields C-4 protonation products, type D allenyl ketones. In contrast, nitro-substituted diynes gave only allenyl ketones (type C and type D) via T-1 excited states. (C) 1997 Elsevier Science S.A.