New insight into the reaction of singlet oxygen with sulfur-containing cyclic alkenes: dye-sensitized photooxygenation of 5,6-dihydro-1,4-dithiins.
The reaction of 3-methyl-5,6-dihydro-1,4-dithiins with singlet oxygen affords dicarbonyl compounds and/or ring-contracted ketosulfoxides, the latter regio- and stereoselectively, depending on the nature of the substituent at C-2 and on the reaction conditions. In competition with normal fragmentation, the intermediate dioxetanes, derived from [2 + 2] cycloaddition of singlet oxygen to the double bond, undergo an intramolecular oxygen transfer to the sulfur-1 atom, leading to labile epoxide intermediates. The latter convert to cis- and trans-ketosulfoxides through a non-concerted S-4 migration. This pathway is promoted by the electron-withdrawing group at C-2 and, for monosubstituted amide, by the solvent basicity. S-Oxidation of dithiins is insignificant, except for the monosubstituted amide derivative or in the presence of protic species, and occurs selectively at the S-1 atom.
Dipartimento di Chimica Organica e Biochimica, Università degli Studi di Napoli Federico II, Complesso Universitario Monte Sant' Angelo, via Cinthia, I-80126, Napoli, Italy.
Flavio
F
Cermola
Annalisa
A
Guaragna
Maria Rosaria
MR
Iesce
Giovanni
G
Palumbo
Raffaella
R
Purcaro
Maria
M
Rubino
Angela
A
Tuzi
D004396:Coloring Agents / Q000737:chemistry*; D003500:Cyclization; D003516:Cycloparaffins / Q000737:chemistry*; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010777:Photochemistry; D012680:Sensitivity and Specificity; D026082:Singlet Oxygen / Q000737:chemistry*; D013237:Stereoisomerism; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013454:Sulfoxides / Q000138:chemical synthesis / Q000737:chemistry
D004396:Coloring Agents; D003516:Cycloparaffins; D006573:Heterocyclic Compounds, 1-Ring; D013438:Sulfhydryl Compounds; D013454:Sulfoxides; D026082:Singlet Oxygen