We have found a specific reaction between ketone 1 and peroxynitrite (ONOO-), rather than other reactive oxygen species and reactive nitrogen species generated in the biological system. On the basis of this reaction, we have successfully developed a new fluorescent probe HKGreen-1, which is highly selective for the detection of peroxynitrite in living cells. Before the oxidation with peroxynitrite, the dichlorofluorescein part is masked and the probe is nonfluorescent. However, upon reaction with peroxynitrite, the fluorophore is released, resulting in strong enhancement in fluorescence intensity.

We found that dioxiranes generated in situ from ketones 1-6 and Oxone underwent intramolecular oxidation of unactivated C-H bonds at delta sites of ketones to yield tetrahydropyrans. From the trans/cis ratio of oxidation products 1a and 2a as well as the retention of the configuration at the delta site of ketone 5, we proposed that the oxidation reaction proceeds through a concerted pathway under a spiro transition state. The intramolecular oxidation of ketone 6 showed the preference for a tertiary delta C-H bond over a secondary one. This intramolecular oxidation method can be extended to the oxidation of the tertiary gamma' C-H bond of ketones 9 and 10. For ketone 11 with two delta C-H bonds and one gamma' C-H bond linked respectively by a sp(3) hydrocarbon tether and a sp(2) ester tether, the oxidation took place exclusively at the delta C-H bonds. Finally, by introducing proper tethers, regioselective hydroxylation of steroid ketones 12-14 have been achieved at the C-17, C-16, C-3, and C-5 positions.

Oxidation Oxidation O 0212Investigation on the Regioselectivities of Intramolecular Oxidation of Unactivated C-H Bonds by Dioxiranes Generated in situ. -It is found that activated ketones in the presence of Oxone undergo highly regioselective intramolecular oxidation at the δ-position to give tetrahydropyran derivatives. This reaction proceeds with retention of configuration and exhibits strong preference for tertiary C-H bonds over secondary ones. Ketones which do not contain δ-CH bonds can undergo hydrolysis or novel intramolecular oxidation at the γ-position. Starting from the steroid (XIII) remote hydroxylation at C-5 is possible. -(WONG, M.-K.; CHUNG, N.-W.; HE, L.; WANG, X.-C.; YAN, Z.; TANG, Y.-C.; YANG*, D.; J.

Pyran derivatives Pyran derivatives R 0340Substituent Effects on Regioselective Intramolecular Oxidation of Unactivated C-H Bonds: Stereoselective Synthesis of Substituted Tetrahydropyrans. -It is found that substituents at the aliphatic carbon chain exhibit remarkable effects on the stereoselectivity of intramolecular oxidation reactions. Besides steric effects observed in the oxidation of ketones bearing methyl and phthalimido groups, an unexpected hydrogen bonding interaction plays an important role on the stereoselective outcome of oxidation of ketones having oxygen substituents. Starting from ketones containing β-oxygen substituents reversed stereoselectivity is observed. -(WONG, M.-K.; CHUNG, N.-W.; HE, L.; YANG*, D.; J.