Dibenzothiophene-5-oxide (DBTO) cleanly produces dibenzothiophene (DBT) on direct photolysis, but with very low quantum yield. A proposed mechanism involves scission of the S−O bond which is coupled to an intersystem crossing step, thus producing the sulfide and O(3P) via a unimolecular pathway. To test this hypothesis, heavy atom substituted DBTOs were prepared and photolyzed. Iodo-, bromo-, and chlorosubstituted DBTOs show higher quantum yields for deoxygenation than does the parent molecule, in the order consistent with an intersystem crossing-related heavy atom effect. 2-Iododibenzothiophene also undergoes photochemical deiodination. Phosphorescence data are consistent with heavy-atom assisted intersystem crossing. Dibenzothiophene-5-oxide (DBTO) cleanly produces dibenzothiophene (DBT) on direct photolysis, but with very low quantum yield. A proposed mechanism involves scission of the S-O bond which is coupled to an intersystem crossing step, thus producing the sulfide and O( 3 P) via a unimolecular pathway. To test this hypothesis, heavy atom substituted DBTOs were prepared and photolyzed. Iodo-, bromo-, and chloro-substituted DBTOs show higher quantum yields for deoxygenation than does the parent molecule, in the order consistent with an intersystem crossing-related heavy atom effect. 2-Iododibenzothiophene also undergoes photochemical deiodination. Phosphorescence data are consistent with heavy-atom assisted intersystem crossing.

Photolysis of aromatic sulfoxides in the presence of alkoxides in alcoholic solvents provides a photochemical route to the corresponding sulfides. Other electron donors also give sulfide with various degrees of success. The reaction could also be carried out using carbazoles as sensitizers, and quantitative yields could be obtained using N-methylcarbazole in methanol. Evidence points toward a hydroxysulfuranyl radical as the key intermediate, and solvent effects point to heterolysis, rather than homolysis, as the step that breaks the S-O bond.

B3LYP, MPW1K, and CCSD(T) electronic structure calculations were employed to investigate the mechanisms for the addition of singlet carbene analogues dimethylsilylene, Me2Si:, dimethylgermylene, Me2Ge:, and dimethylstannylene, Me2Sn:, to 1,3-butadiene to form 1,1-dimethylmetallacyclopent-3-enes and their reverse retro-addition reactions. The calculations suggest that silylenes and germylenes add to 1,3-butadiene to form the 1,2-adduct, vinylmetalliranes, and the 1,4-adduct, metallacyclopent-3-enes, via 1,2-addition and concerted 1,4-addition processes, respectively, while stannylenes add exclusively to form the 1,4-adduct. Our calculations also predict that direct rearrangements of vinylmetalliranes make minimal contribution to the formation of the 1,4-adducts since the retro-addition reactions of the metallylenes followed by 1,4-addition are much faster than the rearrangement reactions of vinylmetalliranes to form metallacyclopent-3-enes.

1,1-Diorgano-1-stannacyclopent-3-enes have been synthesized by condensation in THF of magnesium complexes of 1,3-dienes and dichlorodiorganostannanes. 1,1-Dimethyl-, 1,1-di-n-butyl-, 1,1-di-tert-butyl-, and 1,1-diphenyl-1-stannacyclopent-3-enes and 1,1,3,4-tetramethyl-, 1,1-di-tert-butyl-3,4-dimethyl-, and 3,4-dimethyl-1,1-diphenyl-1-stannacyclopent-3-enes were prepared. Kinetic studies of the pyrolysis at temperatures as low as 75°C of several of these stannacyclopent-3-enes resulted in their first-order disappearance, consistent with a unimolecular dissociation to the corresponding stannylene and diene. Activation parameters are reported. Trapping of dimethylstannylene by dienes was overwhelmed by oligomerization of Me 2 Sn:, but for t-Bu 2 Sn: a high yield of diene adduct was obtained. The dimethylstannylene oligomer(s) functioned as stannylenoids and were responsible for several reactions previously attributed to free Me 2 Sn:. cyclo-(t-Bu 2 Sn) 4 may also function as a stannylenoid.

Photolyses of dibenzothiophene sulfoxides (DBTOs) with intramolecular trapping functionalities attached in the 4-position show higher quantum yields of deoxygenation. Deoxygenation quantum yields are also less solvent dependent for the substituted DBTOs. Product analysis shows a detectable amount of intramolecular O-trapped products and suggests that solvent effects observed in previous studies of DBTO derive at least mainly from the reactivity between the oxidizing species that is released, presumably O(3P), and the solvent, rather than from other macroscopic solvent parameters. DisciplinesChemistry | Organic Chemistry | Other Chemistry | Polymer Chemistry CommentsReprinted (adapted) with permission from The Journal of Organic Chemistry, 70 (9) Photolyses of dibenzothiophene sulfoxides (DBTOs) with intramolecular trapping functionalities attached in the 4-position show higher quantum yields of deoxygenation. Deoxygenation quantum yields are also less solvent dependent for the substituted DBTOs. Product analysis shows a detectable amount of intramolecular O-trapped products and suggests that solvent effects observed in previous studies of DBTO derive at least mainly from the reactivity between the oxidizing species that is released, presumably O( 3 P), and the solvent, rather than from other macroscopic solvent parameters.