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

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 x 10(8) M-1/s(-1) in D2O) due to the mesomeric interactions between oxygen and the naphthalene ring. However, the unstable endoperoxide was immediately and quantitatively decomposed into the aldehyde ester 6. When a methylene linker separates the oxygen from the aromatic core (5), photooxidation leads to a mixture of 1,4 and 5,8-endoperoxides. (C) 2000 Elsevier Science Ltd. All rights reserved.