Effects of oxygenated substituents on the [4+2] cycloaddition of singlet oxygen in the photooxygenation of water-soluble naphthyl ethers

摘要

Water-soluble ethers 2 and 5 undergo [4+2] cycloaddition of singlet oxygen to afford endoperoxides. Compound 2 is extremely reactive (k_r+k_q=2.0×10~8 M~(-1)/s~(-1) in D_2O) due to the mesomeric interactions between oxygen and the naphthalene ring. However, the unstable endoperoxide was immediately and quantitatively decomposed intot eh aldehyde ester 6. When a methylene linker separates the oxygen from the aromatic core (5), photooxidation leads to a mixture f 1,4 and 5,8-endoperoxides.